mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2024-12-28 16:53:49 +00:00
docs: scheduler: convert docs to ReST and rename to *.rst
In order to prepare to add them to the Kernel API book, convert the files to ReST format. The conversion is actually: - add blank lines and identation in order to identify paragraphs; - fix tables markups; - add some lists markups; - mark literal blocks; - adjust title markups. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mauro Carvalho Chehab
Jonathan Corbet
parent
d223884089
commit
d6a3b24762
@ -11,4 +11,4 @@ Description:
|
||||
example would be, if User A has shares = 1024 and user
|
||||
B has shares = 2048, User B will get twice the CPU
|
||||
bandwidth user A will. For more details refer
|
||||
Documentation/scheduler/sched-design-CFS.txt
|
||||
Documentation/scheduler/sched-design-CFS.rst
|
||||
|
||||
@ -1,3 +1,4 @@
|
||||
================================================
|
||||
Completions - "wait for completion" barrier APIs
|
||||
================================================
|
||||
|
||||
@ -46,7 +47,7 @@ it has to wait for it.
|
||||
|
||||
To use completions you need to #include <linux/completion.h> and
|
||||
create a static or dynamic variable of type 'struct completion',
|
||||
which has only two fields:
|
||||
which has only two fields::
|
||||
|
||||
struct completion {
|
||||
unsigned int done;
|
||||
@ -57,7 +58,7 @@ This provides the ->wait waitqueue to place tasks on for waiting (if any), and
|
||||
the ->done completion flag for indicating whether it's completed or not.
|
||||
|
||||
Completions should be named to refer to the event that is being synchronized on.
|
||||
A good example is:
|
||||
A good example is::
|
||||
|
||||
wait_for_completion(&early_console_added);
|
||||
|
||||
@ -81,7 +82,7 @@ have taken place, even if these wait functions return prematurely due to a timeo
|
||||
or a signal triggering.
|
||||
|
||||
Initializing of dynamically allocated completion objects is done via a call to
|
||||
init_completion():
|
||||
init_completion()::
|
||||
|
||||
init_completion(&dynamic_object->done);
|
||||
|
||||
@ -100,7 +101,8 @@ but be aware of other races.
|
||||
|
||||
For static declaration and initialization, macros are available.
|
||||
|
||||
For static (or global) declarations in file scope you can use DECLARE_COMPLETION():
|
||||
For static (or global) declarations in file scope you can use
|
||||
DECLARE_COMPLETION()::
|
||||
|
||||
static DECLARE_COMPLETION(setup_done);
|
||||
DECLARE_COMPLETION(setup_done);
|
||||
@ -111,7 +113,7 @@ initialized to 'not done' and doesn't require an init_completion() call.
|
||||
When a completion is declared as a local variable within a function,
|
||||
then the initialization should always use DECLARE_COMPLETION_ONSTACK()
|
||||
explicitly, not just to make lockdep happy, but also to make it clear
|
||||
that limited scope had been considered and is intentional:
|
||||
that limited scope had been considered and is intentional::
|
||||
|
||||
DECLARE_COMPLETION_ONSTACK(setup_done)
|
||||
|
||||
@ -140,11 +142,11 @@ Waiting for completions:
|
||||
------------------------
|
||||
|
||||
For a thread to wait for some concurrent activity to finish, it
|
||||
calls wait_for_completion() on the initialized completion structure:
|
||||
calls wait_for_completion() on the initialized completion structure::
|
||||
|
||||
void wait_for_completion(struct completion *done)
|
||||
|
||||
A typical usage scenario is:
|
||||
A typical usage scenario is::
|
||||
|
||||
CPU#1 CPU#2
|
||||
|
||||
@ -192,17 +194,17 @@ A common problem that occurs is to have unclean assignment of return types,
|
||||
so take care to assign return-values to variables of the proper type.
|
||||
|
||||
Checking for the specific meaning of return values also has been found
|
||||
to be quite inaccurate, e.g. constructs like:
|
||||
to be quite inaccurate, e.g. constructs like::
|
||||
|
||||
if (!wait_for_completion_interruptible_timeout(...))
|
||||
|
||||
... would execute the same code path for successful completion and for the
|
||||
interrupted case - which is probably not what you want.
|
||||
interrupted case - which is probably not what you want::
|
||||
|
||||
int wait_for_completion_interruptible(struct completion *done)
|
||||
|
||||
This function marks the task TASK_INTERRUPTIBLE while it is waiting.
|
||||
If a signal was received while waiting it will return -ERESTARTSYS; 0 otherwise.
|
||||
If a signal was received while waiting it will return -ERESTARTSYS; 0 otherwise::
|
||||
|
||||
unsigned long wait_for_completion_timeout(struct completion *done, unsigned long timeout)
|
||||
|
||||
@ -214,7 +216,7 @@ Timeouts are preferably calculated with msecs_to_jiffies() or usecs_to_jiffies()
|
||||
to make the code largely HZ-invariant.
|
||||
|
||||
If the returned timeout value is deliberately ignored a comment should probably explain
|
||||
why (e.g. see drivers/mfd/wm8350-core.c wm8350_read_auxadc()).
|
||||
why (e.g. see drivers/mfd/wm8350-core.c wm8350_read_auxadc())::
|
||||
|
||||
long wait_for_completion_interruptible_timeout(struct completion *done, unsigned long timeout)
|
||||
|
||||
@ -225,14 +227,14 @@ jiffies if completion occurred.
|
||||
|
||||
Further variants include _killable which uses TASK_KILLABLE as the
|
||||
designated tasks state and will return -ERESTARTSYS if it is interrupted,
|
||||
or 0 if completion was achieved. There is a _timeout variant as well:
|
||||
or 0 if completion was achieved. There is a _timeout variant as well::
|
||||
|
||||
long wait_for_completion_killable(struct completion *done)
|
||||
long wait_for_completion_killable_timeout(struct completion *done, unsigned long timeout)
|
||||
|
||||
The _io variants wait_for_completion_io() behave the same as the non-_io
|
||||
variants, except for accounting waiting time as 'waiting on IO', which has
|
||||
an impact on how the task is accounted in scheduling/IO stats:
|
||||
an impact on how the task is accounted in scheduling/IO stats::
|
||||
|
||||
void wait_for_completion_io(struct completion *done)
|
||||
unsigned long wait_for_completion_io_timeout(struct completion *done, unsigned long timeout)
|
||||
@ -243,11 +245,11 @@ Signaling completions:
|
||||
|
||||
A thread that wants to signal that the conditions for continuation have been
|
||||
achieved calls complete() to signal exactly one of the waiters that it can
|
||||
continue:
|
||||
continue::
|
||||
|
||||
void complete(struct completion *done)
|
||||
|
||||
... or calls complete_all() to signal all current and future waiters:
|
||||
... or calls complete_all() to signal all current and future waiters::
|
||||
|
||||
void complete_all(struct completion *done)
|
||||
|
||||
@ -268,7 +270,7 @@ probably are a design bug.
|
||||
|
||||
Signaling completion from IRQ context is fine as it will appropriately
|
||||
lock with spin_lock_irqsave()/spin_unlock_irqrestore() and it will never
|
||||
sleep.
|
||||
sleep.
|
||||
|
||||
|
||||
try_wait_for_completion()/completion_done():
|
||||
@ -276,14 +278,14 @@ try_wait_for_completion()/completion_done():
|
||||
|
||||
The try_wait_for_completion() function will not put the thread on the wait
|
||||
queue but rather returns false if it would need to enqueue (block) the thread,
|
||||
else it consumes one posted completion and returns true.
|
||||
else it consumes one posted completion and returns true::
|
||||
|
||||
bool try_wait_for_completion(struct completion *done)
|
||||
|
||||
Finally, to check the state of a completion without changing it in any way,
|
||||
call completion_done(), which returns false if there are no posted
|
||||
completions that were not yet consumed by waiters (implying that there are
|
||||
waiters) and true otherwise;
|
||||
waiters) and true otherwise::
|
||||
|
||||
bool completion_done(struct completion *done)
|
||||
|
||||
29
Documentation/scheduler/index.rst
Normal file
29
Documentation/scheduler/index.rst
Normal file
@ -0,0 +1,29 @@
|
||||
:orphan:
|
||||
|
||||
===============
|
||||
Linux Scheduler
|
||||
===============
|
||||
|
||||
.. toctree::
|
||||
:maxdepth: 1
|
||||
|
||||
|
||||
completion
|
||||
sched-arch
|
||||
sched-bwc
|
||||
sched-deadline
|
||||
sched-design-CFS
|
||||
sched-domains
|
||||
sched-energy
|
||||
sched-nice-design
|
||||
sched-rt-group
|
||||
sched-stats
|
||||
|
||||
text_files
|
||||
|
||||
.. only:: subproject and html
|
||||
|
||||
Indices
|
||||
=======
|
||||
|
||||
* :ref:`genindex`
|
||||
@ -1,4 +1,6 @@
|
||||
CPU Scheduler implementation hints for architecture specific code
|
||||
=================================================================
|
||||
CPU Scheduler implementation hints for architecture specific code
|
||||
=================================================================
|
||||
|
||||
Nick Piggin, 2005
|
||||
|
||||
@ -35,9 +37,10 @@ Your cpu_idle routines need to obey the following rules:
|
||||
4. The only time interrupts need to be disabled when checking
|
||||
need_resched is if we are about to sleep the processor until
|
||||
the next interrupt (this doesn't provide any protection of
|
||||
need_resched, it prevents losing an interrupt).
|
||||
need_resched, it prevents losing an interrupt):
|
||||
|
||||
4a. Common problem with this type of sleep appears to be::
|
||||
|
||||
4a. Common problem with this type of sleep appears to be:
|
||||
local_irq_disable();
|
||||
if (!need_resched()) {
|
||||
local_irq_enable();
|
||||
@ -51,10 +54,10 @@ Your cpu_idle routines need to obey the following rules:
|
||||
although it may be reasonable to do some background work or enter
|
||||
a low CPU priority.
|
||||
|
||||
5a. If TIF_POLLING_NRFLAG is set, and we do decide to enter
|
||||
an interrupt sleep, it needs to be cleared then a memory
|
||||
barrier issued (followed by a test of need_resched with
|
||||
interrupts disabled, as explained in 3).
|
||||
- 5a. If TIF_POLLING_NRFLAG is set, and we do decide to enter
|
||||
an interrupt sleep, it needs to be cleared then a memory
|
||||
barrier issued (followed by a test of need_resched with
|
||||
interrupts disabled, as explained in 3).
|
||||
|
||||
arch/x86/kernel/process.c has examples of both polling and
|
||||
sleeping idle functions.
|
||||
@ -71,4 +74,3 @@ sh64 - Is sleeping racy vs interrupts? (See #4a)
|
||||
|
||||
sparc - IRQs on at this point(?), change local_irq_save to _disable.
|
||||
- TODO: needs secondary CPUs to disable preempt (See #1)
|
||||
|
||||
@ -1,8 +1,9 @@
|
||||
=====================
|
||||
CFS Bandwidth Control
|
||||
=====================
|
||||
|
||||
[ This document only discusses CPU bandwidth control for SCHED_NORMAL.
|
||||
The SCHED_RT case is covered in Documentation/scheduler/sched-rt-group.txt ]
|
||||
The SCHED_RT case is covered in Documentation/scheduler/sched-rt-group.rst ]
|
||||
|
||||
CFS bandwidth control is a CONFIG_FAIR_GROUP_SCHED extension which allows the
|
||||
specification of the maximum CPU bandwidth available to a group or hierarchy.
|
||||
@ -27,7 +28,8 @@ cpu.cfs_quota_us: the total available run-time within a period (in microseconds)
|
||||
cpu.cfs_period_us: the length of a period (in microseconds)
|
||||
cpu.stat: exports throttling statistics [explained further below]
|
||||
|
||||
The default values are:
|
||||
The default values are::
|
||||
|
||||
cpu.cfs_period_us=100ms
|
||||
cpu.cfs_quota=-1
|
||||
|
||||
@ -55,7 +57,8 @@ For efficiency run-time is transferred between the global pool and CPU local
|
||||
on large systems. The amount transferred each time such an update is required
|
||||
is described as the "slice".
|
||||
|
||||
This is tunable via procfs:
|
||||
This is tunable via procfs::
|
||||
|
||||
/proc/sys/kernel/sched_cfs_bandwidth_slice_us (default=5ms)
|
||||
|
||||
Larger slice values will reduce transfer overheads, while smaller values allow
|
||||
@ -66,6 +69,7 @@ Statistics
|
||||
A group's bandwidth statistics are exported via 3 fields in cpu.stat.
|
||||
|
||||
cpu.stat:
|
||||
|
||||
- nr_periods: Number of enforcement intervals that have elapsed.
|
||||
- nr_throttled: Number of times the group has been throttled/limited.
|
||||
- throttled_time: The total time duration (in nanoseconds) for which entities
|
||||
@ -78,12 +82,15 @@ Hierarchical considerations
|
||||
The interface enforces that an individual entity's bandwidth is always
|
||||
attainable, that is: max(c_i) <= C. However, over-subscription in the
|
||||
aggregate case is explicitly allowed to enable work-conserving semantics
|
||||
within a hierarchy.
|
||||
within a hierarchy:
|
||||
|
||||
e.g. \Sum (c_i) may exceed C
|
||||
|
||||
[ Where C is the parent's bandwidth, and c_i its children ]
|
||||
|
||||
|
||||
There are two ways in which a group may become throttled:
|
||||
|
||||
a. it fully consumes its own quota within a period
|
||||
b. a parent's quota is fully consumed within its period
|
||||
|
||||
@ -92,7 +99,7 @@ be allowed to until the parent's runtime is refreshed.
|
||||
|
||||
Examples
|
||||
--------
|
||||
1. Limit a group to 1 CPU worth of runtime.
|
||||
1. Limit a group to 1 CPU worth of runtime::
|
||||
|
||||
If period is 250ms and quota is also 250ms, the group will get
|
||||
1 CPU worth of runtime every 250ms.
|
||||
@ -100,10 +107,10 @@ Examples
|
||||
# echo 250000 > cpu.cfs_quota_us /* quota = 250ms */
|
||||
# echo 250000 > cpu.cfs_period_us /* period = 250ms */
|
||||
|
||||
2. Limit a group to 2 CPUs worth of runtime on a multi-CPU machine.
|
||||
2. Limit a group to 2 CPUs worth of runtime on a multi-CPU machine
|
||||
|
||||
With 500ms period and 1000ms quota, the group can get 2 CPUs worth of
|
||||
runtime every 500ms.
|
||||
With 500ms period and 1000ms quota, the group can get 2 CPUs worth of
|
||||
runtime every 500ms::
|
||||
|
||||
# echo 1000000 > cpu.cfs_quota_us /* quota = 1000ms */
|
||||
# echo 500000 > cpu.cfs_period_us /* period = 500ms */
|
||||
@ -112,11 +119,10 @@ Examples
|
||||
|
||||
3. Limit a group to 20% of 1 CPU.
|
||||
|
||||
With 50ms period, 10ms quota will be equivalent to 20% of 1 CPU.
|
||||
With 50ms period, 10ms quota will be equivalent to 20% of 1 CPU::
|
||||
|
||||
# echo 10000 > cpu.cfs_quota_us /* quota = 10ms */
|
||||
# echo 50000 > cpu.cfs_period_us /* period = 50ms */
|
||||
|
||||
By using a small period here we are ensuring a consistent latency
|
||||
response at the expense of burst capacity.
|
||||
|
||||
By using a small period here we are ensuring a consistent latency
|
||||
response at the expense of burst capacity.
|
||||
@ -1,29 +1,29 @@
|
||||
Deadline Task Scheduling
|
||||
------------------------
|
||||
========================
|
||||
Deadline Task Scheduling
|
||||
========================
|
||||
|
||||
CONTENTS
|
||||
========
|
||||
.. CONTENTS
|
||||
|
||||
0. WARNING
|
||||
1. Overview
|
||||
2. Scheduling algorithm
|
||||
2.1 Main algorithm
|
||||
2.2 Bandwidth reclaiming
|
||||
3. Scheduling Real-Time Tasks
|
||||
3.1 Definitions
|
||||
3.2 Schedulability Analysis for Uniprocessor Systems
|
||||
3.3 Schedulability Analysis for Multiprocessor Systems
|
||||
3.4 Relationship with SCHED_DEADLINE Parameters
|
||||
4. Bandwidth management
|
||||
4.1 System-wide settings
|
||||
4.2 Task interface
|
||||
4.3 Default behavior
|
||||
4.4 Behavior of sched_yield()
|
||||
5. Tasks CPU affinity
|
||||
5.1 SCHED_DEADLINE and cpusets HOWTO
|
||||
6. Future plans
|
||||
A. Test suite
|
||||
B. Minimal main()
|
||||
0. WARNING
|
||||
1. Overview
|
||||
2. Scheduling algorithm
|
||||
2.1 Main algorithm
|
||||
2.2 Bandwidth reclaiming
|
||||
3. Scheduling Real-Time Tasks
|
||||
3.1 Definitions
|
||||
3.2 Schedulability Analysis for Uniprocessor Systems
|
||||
3.3 Schedulability Analysis for Multiprocessor Systems
|
||||
3.4 Relationship with SCHED_DEADLINE Parameters
|
||||
4. Bandwidth management
|
||||
4.1 System-wide settings
|
||||
4.2 Task interface
|
||||
4.3 Default behavior
|
||||
4.4 Behavior of sched_yield()
|
||||
5. Tasks CPU affinity
|
||||
5.1 SCHED_DEADLINE and cpusets HOWTO
|
||||
6. Future plans
|
||||
A. Test suite
|
||||
B. Minimal main()
|
||||
|
||||
|
||||
0. WARNING
|
||||
@ -44,7 +44,7 @@ CONTENTS
|
||||
|
||||
|
||||
2. Scheduling algorithm
|
||||
==================
|
||||
=======================
|
||||
|
||||
2.1 Main algorithm
|
||||
------------------
|
||||
@ -80,7 +80,7 @@ CONTENTS
|
||||
a "remaining runtime". These two parameters are initially set to 0;
|
||||
|
||||
- When a SCHED_DEADLINE task wakes up (becomes ready for execution),
|
||||
the scheduler checks if
|
||||
the scheduler checks if::
|
||||
|
||||
remaining runtime runtime
|
||||
---------------------------------- > ---------
|
||||
@ -97,7 +97,7 @@ CONTENTS
|
||||
left unchanged;
|
||||
|
||||
- When a SCHED_DEADLINE task executes for an amount of time t, its
|
||||
remaining runtime is decreased as
|
||||
remaining runtime is decreased as::
|
||||
|
||||
remaining runtime = remaining runtime - t
|
||||
|
||||
@ -112,7 +112,7 @@ CONTENTS
|
||||
|
||||
- When the current time is equal to the replenishment time of a
|
||||
throttled task, the scheduling deadline and the remaining runtime are
|
||||
updated as
|
||||
updated as::
|
||||
|
||||
scheduling deadline = scheduling deadline + period
|
||||
remaining runtime = remaining runtime + runtime
|
||||
@ -129,7 +129,7 @@ CONTENTS
|
||||
Reclamation of Unused Bandwidth) algorithm [15, 16, 17] and it is enabled
|
||||
when flag SCHED_FLAG_RECLAIM is set.
|
||||
|
||||
The following diagram illustrates the state names for tasks handled by GRUB:
|
||||
The following diagram illustrates the state names for tasks handled by GRUB::
|
||||
|
||||
------------
|
||||
(d) | Active |
|
||||
@ -168,7 +168,7 @@ CONTENTS
|
||||
breaking the real-time guarantees.
|
||||
|
||||
The 0-lag time for a task entering the ActiveNonContending state is
|
||||
computed as
|
||||
computed as::
|
||||
|
||||
(runtime * dl_period)
|
||||
deadline - ---------------------
|
||||
@ -183,7 +183,7 @@ CONTENTS
|
||||
the task's utilization must be removed from the previous runqueue's active
|
||||
utilization and must be added to the new runqueue's active utilization.
|
||||
In order to avoid races between a task waking up on a runqueue while the
|
||||
"inactive timer" is running on a different CPU, the "dl_non_contending"
|
||||
"inactive timer" is running on a different CPU, the "dl_non_contending"
|
||||
flag is used to indicate that a task is not on a runqueue but is active
|
||||
(so, the flag is set when the task blocks and is cleared when the
|
||||
"inactive timer" fires or when the task wakes up).
|
||||
@ -222,36 +222,36 @@ CONTENTS
|
||||
|
||||
|
||||
Let's now see a trivial example of two deadline tasks with runtime equal
|
||||
to 4 and period equal to 8 (i.e., bandwidth equal to 0.5):
|
||||
to 4 and period equal to 8 (i.e., bandwidth equal to 0.5)::
|
||||
|
||||
A Task T1
|
||||
|
|
||||
| |
|
||||
| |
|
||||
|-------- |----
|
||||
| | V
|
||||
|---|---|---|---|---|---|---|---|--------->t
|
||||
0 1 2 3 4 5 6 7 8
|
||||
A Task T1
|
||||
|
|
||||
| |
|
||||
| |
|
||||
|-------- |----
|
||||
| | V
|
||||
|---|---|---|---|---|---|---|---|--------->t
|
||||
0 1 2 3 4 5 6 7 8
|
||||
|
||||
|
||||
A Task T2
|
||||
|
|
||||
| |
|
||||
| |
|
||||
| ------------------------|
|
||||
| | V
|
||||
|---|---|---|---|---|---|---|---|--------->t
|
||||
0 1 2 3 4 5 6 7 8
|
||||
A Task T2
|
||||
|
|
||||
| |
|
||||
| |
|
||||
| ------------------------|
|
||||
| | V
|
||||
|---|---|---|---|---|---|---|---|--------->t
|
||||
0 1 2 3 4 5 6 7 8
|
||||
|
||||
|
||||
A running_bw
|
||||
|
|
||||
1 ----------------- ------
|
||||
| | |
|
||||
0.5- -----------------
|
||||
| |
|
||||
|---|---|---|---|---|---|---|---|--------->t
|
||||
0 1 2 3 4 5 6 7 8
|
||||
A running_bw
|
||||
|
|
||||
1 ----------------- ------
|
||||
| | |
|
||||
0.5- -----------------
|
||||
| |
|
||||
|---|---|---|---|---|---|---|---|--------->t
|
||||
0 1 2 3 4 5 6 7 8
|
||||
|
||||
|
||||
- Time t = 0:
|
||||
@ -284,7 +284,7 @@ CONTENTS
|
||||
|
||||
|
||||
2.3 Energy-aware scheduling
|
||||
------------------------
|
||||
---------------------------
|
||||
|
||||
When cpufreq's schedutil governor is selected, SCHED_DEADLINE implements the
|
||||
GRUB-PA [19] algorithm, reducing the CPU operating frequency to the minimum
|
||||
@ -299,15 +299,20 @@ CONTENTS
|
||||
3. Scheduling Real-Time Tasks
|
||||
=============================
|
||||
|
||||
* BIG FAT WARNING ******************************************************
|
||||
*
|
||||
* This section contains a (not-thorough) summary on classical deadline
|
||||
* scheduling theory, and how it applies to SCHED_DEADLINE.
|
||||
* The reader can "safely" skip to Section 4 if only interested in seeing
|
||||
* how the scheduling policy can be used. Anyway, we strongly recommend
|
||||
* to come back here and continue reading (once the urge for testing is
|
||||
* satisfied :P) to be sure of fully understanding all technical details.
|
||||
************************************************************************
|
||||
|
||||
|
||||
.. BIG FAT WARNING ******************************************************
|
||||
|
||||
.. warning::
|
||||
|
||||
This section contains a (not-thorough) summary on classical deadline
|
||||
scheduling theory, and how it applies to SCHED_DEADLINE.
|
||||
The reader can "safely" skip to Section 4 if only interested in seeing
|
||||
how the scheduling policy can be used. Anyway, we strongly recommend
|
||||
to come back here and continue reading (once the urge for testing is
|
||||
satisfied :P) to be sure of fully understanding all technical details.
|
||||
|
||||
.. ************************************************************************
|
||||
|
||||
There are no limitations on what kind of task can exploit this new
|
||||
scheduling discipline, even if it must be said that it is particularly
|
||||
@ -329,6 +334,7 @@ CONTENTS
|
||||
sporadic with minimum inter-arrival time P is r_{j+1} >= r_j + P. Finally,
|
||||
d_j = r_j + D, where D is the task's relative deadline.
|
||||
Summing up, a real-time task can be described as
|
||||
|
||||
Task = (WCET, D, P)
|
||||
|
||||
The utilization of a real-time task is defined as the ratio between its
|
||||
@ -352,13 +358,15 @@ CONTENTS
|
||||
between the finishing time of a job and its absolute deadline).
|
||||
More precisely, it can be proven that using a global EDF scheduler the
|
||||
maximum tardiness of each task is smaller or equal than
|
||||
|
||||
((M − 1) · WCET_max − WCET_min)/(M − (M − 2) · U_max) + WCET_max
|
||||
|
||||
where WCET_max = max{WCET_i} is the maximum WCET, WCET_min=min{WCET_i}
|
||||
is the minimum WCET, and U_max = max{WCET_i/P_i} is the maximum
|
||||
utilization[12].
|
||||
|
||||
3.2 Schedulability Analysis for Uniprocessor Systems
|
||||
------------------------
|
||||
----------------------------------------------------
|
||||
|
||||
If M=1 (uniprocessor system), or in case of partitioned scheduling (each
|
||||
real-time task is statically assigned to one and only one CPU), it is
|
||||
@ -370,7 +378,9 @@ CONTENTS
|
||||
a task as WCET_i/min{D_i,P_i}, and EDF is able to respect all the deadlines
|
||||
of all the tasks running on a CPU if the sum of the densities of the tasks
|
||||
running on such a CPU is smaller or equal than 1:
|
||||
|
||||
sum(WCET_i / min{D_i, P_i}) <= 1
|
||||
|
||||
It is important to notice that this condition is only sufficient, and not
|
||||
necessary: there are task sets that are schedulable, but do not respect the
|
||||
condition. For example, consider the task set {Task_1,Task_2} composed by
|
||||
@ -379,7 +389,9 @@ CONTENTS
|
||||
(Task_1 is scheduled as soon as it is released, and finishes just in time
|
||||
to respect its deadline; Task_2 is scheduled immediately after Task_1, hence
|
||||
its response time cannot be larger than 50ms + 10ms = 60ms) even if
|
||||
|
||||
50 / min{50,100} + 10 / min{100, 100} = 50 / 50 + 10 / 100 = 1.1
|
||||
|
||||
Of course it is possible to test the exact schedulability of tasks with
|
||||
D_i != P_i (checking a condition that is both sufficient and necessary),
|
||||
but this cannot be done by comparing the total utilization or density with
|
||||
@ -399,7 +411,7 @@ CONTENTS
|
||||
4 Linux uses an admission test based on the tasks' utilizations.
|
||||
|
||||
3.3 Schedulability Analysis for Multiprocessor Systems
|
||||
------------------------
|
||||
------------------------------------------------------
|
||||
|
||||
On multiprocessor systems with global EDF scheduling (non partitioned
|
||||
systems), a sufficient test for schedulability can not be based on the
|
||||
@ -428,7 +440,9 @@ CONTENTS
|
||||
between total utilization (or density) and a fixed constant. If all tasks
|
||||
have D_i = P_i, a sufficient schedulability condition can be expressed in
|
||||
a simple way:
|
||||
|
||||
sum(WCET_i / P_i) <= M - (M - 1) · U_max
|
||||
|
||||
where U_max = max{WCET_i / P_i}[10]. Notice that for U_max = 1,
|
||||
M - (M - 1) · U_max becomes M - M + 1 = 1 and this schedulability condition
|
||||
just confirms the Dhall's effect. A more complete survey of the literature
|
||||
@ -447,7 +461,7 @@ CONTENTS
|
||||
the tasks are limited.
|
||||
|
||||
3.4 Relationship with SCHED_DEADLINE Parameters
|
||||
------------------------
|
||||
-----------------------------------------------
|
||||
|
||||
Finally, it is important to understand the relationship between the
|
||||
SCHED_DEADLINE scheduling parameters described in Section 2 (runtime,
|
||||
@ -473,6 +487,7 @@ CONTENTS
|
||||
this task, as it is not possible to respect its temporal constraints.
|
||||
|
||||
References:
|
||||
|
||||
1 - C. L. Liu and J. W. Layland. Scheduling algorithms for multiprogram-
|
||||
ming in a hard-real-time environment. Journal of the Association for
|
||||
Computing Machinery, 20(1), 1973.
|
||||
@ -550,7 +565,7 @@ CONTENTS
|
||||
The interface used to control the CPU bandwidth that can be allocated
|
||||
to -deadline tasks is similar to the one already used for -rt
|
||||
tasks with real-time group scheduling (a.k.a. RT-throttling - see
|
||||
Documentation/scheduler/sched-rt-group.txt), and is based on readable/
|
||||
Documentation/scheduler/sched-rt-group.rst), and is based on readable/
|
||||
writable control files located in procfs (for system wide settings).
|
||||
Notice that per-group settings (controlled through cgroupfs) are still not
|
||||
defined for -deadline tasks, because more discussion is needed in order to
|
||||
@ -596,11 +611,13 @@ CONTENTS
|
||||
Specifying a periodic/sporadic task that executes for a given amount of
|
||||
runtime at each instance, and that is scheduled according to the urgency of
|
||||
its own timing constraints needs, in general, a way of declaring:
|
||||
|
||||
- a (maximum/typical) instance execution time,
|
||||
- a minimum interval between consecutive instances,
|
||||
- a time constraint by which each instance must be completed.
|
||||
|
||||
Therefore:
|
||||
|
||||
* a new struct sched_attr, containing all the necessary fields is
|
||||
provided;
|
||||
* the new scheduling related syscalls that manipulate it, i.e.,
|
||||
@ -658,21 +675,21 @@ CONTENTS
|
||||
------------------------------------
|
||||
|
||||
An example of a simple configuration (pin a -deadline task to CPU0)
|
||||
follows (rt-app is used to create a -deadline task).
|
||||
follows (rt-app is used to create a -deadline task)::
|
||||
|
||||
mkdir /dev/cpuset
|
||||
mount -t cgroup -o cpuset cpuset /dev/cpuset
|
||||
cd /dev/cpuset
|
||||
mkdir cpu0
|
||||
echo 0 > cpu0/cpuset.cpus
|
||||
echo 0 > cpu0/cpuset.mems
|
||||
echo 1 > cpuset.cpu_exclusive
|
||||
echo 0 > cpuset.sched_load_balance
|
||||
echo 1 > cpu0/cpuset.cpu_exclusive
|
||||
echo 1 > cpu0/cpuset.mem_exclusive
|
||||
echo $$ > cpu0/tasks
|
||||
rt-app -t 100000:10000:d:0 -D5 (it is now actually superfluous to specify
|
||||
task affinity)
|
||||
mkdir /dev/cpuset
|
||||
mount -t cgroup -o cpuset cpuset /dev/cpuset
|
||||
cd /dev/cpuset
|
||||
mkdir cpu0
|
||||
echo 0 > cpu0/cpuset.cpus
|
||||
echo 0 > cpu0/cpuset.mems
|
||||
echo 1 > cpuset.cpu_exclusive
|
||||
echo 0 > cpuset.sched_load_balance
|
||||
echo 1 > cpu0/cpuset.cpu_exclusive
|
||||
echo 1 > cpu0/cpuset.mem_exclusive
|
||||
echo $$ > cpu0/tasks
|
||||
rt-app -t 100000:10000:d:0 -D5 # it is now actually superfluous to specify
|
||||
# task affinity
|
||||
|
||||
6. Future plans
|
||||
===============
|
||||
@ -711,7 +728,7 @@ Appendix A. Test suite
|
||||
rt-app is available at: https://github.com/scheduler-tools/rt-app.
|
||||
|
||||
Thread parameters can be specified from the command line, with something like
|
||||
this:
|
||||
this::
|
||||
|
||||
# rt-app -t 100000:10000:d -t 150000:20000:f:10 -D5
|
||||
|
||||
@ -721,27 +738,27 @@ Appendix A. Test suite
|
||||
of 5 seconds.
|
||||
|
||||
More interestingly, configurations can be described with a json file that
|
||||
can be passed as input to rt-app with something like this:
|
||||
can be passed as input to rt-app with something like this::
|
||||
|
||||
# rt-app my_config.json
|
||||
|
||||
The parameters that can be specified with the second method are a superset
|
||||
of the command line options. Please refer to rt-app documentation for more
|
||||
details (<rt-app-sources>/doc/*.json).
|
||||
details (`<rt-app-sources>/doc/*.json`).
|
||||
|
||||
The second testing application is a modification of schedtool, called
|
||||
schedtool-dl, which can be used to setup SCHED_DEADLINE parameters for a
|
||||
certain pid/application. schedtool-dl is available at:
|
||||
https://github.com/scheduler-tools/schedtool-dl.git.
|
||||
|
||||
The usage is straightforward:
|
||||
The usage is straightforward::
|
||||
|
||||
# schedtool -E -t 10000000:100000000 -e ./my_cpuhog_app
|
||||
|
||||
With this, my_cpuhog_app is put to run inside a SCHED_DEADLINE reservation
|
||||
of 10ms every 100ms (note that parameters are expressed in microseconds).
|
||||
You can also use schedtool to create a reservation for an already running
|
||||
application, given that you know its pid:
|
||||
application, given that you know its pid::
|
||||
|
||||
# schedtool -E -t 10000000:100000000 my_app_pid
|
||||
|
||||
@ -750,43 +767,43 @@ Appendix B. Minimal main()
|
||||
|
||||
We provide in what follows a simple (ugly) self-contained code snippet
|
||||
showing how SCHED_DEADLINE reservations can be created by a real-time
|
||||
application developer.
|
||||
application developer::
|
||||
|
||||
#define _GNU_SOURCE
|
||||
#include <unistd.h>
|
||||
#include <stdio.h>
|
||||
#include <stdlib.h>
|
||||
#include <string.h>
|
||||
#include <time.h>
|
||||
#include <linux/unistd.h>
|
||||
#include <linux/kernel.h>
|
||||
#include <linux/types.h>
|
||||
#include <sys/syscall.h>
|
||||
#include <pthread.h>
|
||||
#define _GNU_SOURCE
|
||||
#include <unistd.h>
|
||||
#include <stdio.h>
|
||||
#include <stdlib.h>
|
||||
#include <string.h>
|
||||
#include <time.h>
|
||||
#include <linux/unistd.h>
|
||||
#include <linux/kernel.h>
|
||||
#include <linux/types.h>
|
||||
#include <sys/syscall.h>
|
||||
#include <pthread.h>
|
||||
|
||||
#define gettid() syscall(__NR_gettid)
|
||||
#define gettid() syscall(__NR_gettid)
|
||||
|
||||
#define SCHED_DEADLINE 6
|
||||
#define SCHED_DEADLINE 6
|
||||
|
||||
/* XXX use the proper syscall numbers */
|
||||
#ifdef __x86_64__
|
||||
#define __NR_sched_setattr 314
|
||||
#define __NR_sched_getattr 315
|
||||
#endif
|
||||
/* XXX use the proper syscall numbers */
|
||||
#ifdef __x86_64__
|
||||
#define __NR_sched_setattr 314
|
||||
#define __NR_sched_getattr 315
|
||||
#endif
|
||||
|
||||
#ifdef __i386__
|
||||
#define __NR_sched_setattr 351
|
||||
#define __NR_sched_getattr 352
|
||||
#endif
|
||||
#ifdef __i386__
|
||||
#define __NR_sched_setattr 351
|
||||
#define __NR_sched_getattr 352
|
||||
#endif
|
||||
|
||||
#ifdef __arm__
|
||||
#define __NR_sched_setattr 380
|
||||
#define __NR_sched_getattr 381
|
||||
#endif
|
||||
#ifdef __arm__
|
||||
#define __NR_sched_setattr 380
|
||||
#define __NR_sched_getattr 381
|
||||
#endif
|
||||
|
||||
static volatile int done;
|
||||
static volatile int done;
|
||||
|
||||
struct sched_attr {
|
||||
struct sched_attr {
|
||||
__u32 size;
|
||||
|
||||
__u32 sched_policy;
|
||||
@ -802,25 +819,25 @@ Appendix B. Minimal main()
|
||||
__u64 sched_runtime;
|
||||
__u64 sched_deadline;
|
||||
__u64 sched_period;
|
||||
};
|
||||
};
|
||||
|
||||
int sched_setattr(pid_t pid,
|
||||
int sched_setattr(pid_t pid,
|
||||
const struct sched_attr *attr,
|
||||
unsigned int flags)
|
||||
{
|
||||
{
|
||||
return syscall(__NR_sched_setattr, pid, attr, flags);
|
||||
}
|
||||
}
|
||||
|
||||
int sched_getattr(pid_t pid,
|
||||
int sched_getattr(pid_t pid,
|
||||
struct sched_attr *attr,
|
||||
unsigned int size,
|
||||
unsigned int flags)
|
||||
{
|
||||
{
|
||||
return syscall(__NR_sched_getattr, pid, attr, size, flags);
|
||||
}
|
||||
}
|
||||
|
||||
void *run_deadline(void *data)
|
||||
{
|
||||
void *run_deadline(void *data)
|
||||
{
|
||||
struct sched_attr attr;
|
||||
int x = 0;
|
||||
int ret;
|
||||
@ -851,10 +868,10 @@ Appendix B. Minimal main()
|
||||
|
||||
printf("deadline thread dies [%ld]\n", gettid());
|
||||
return NULL;
|
||||
}
|
||||
}
|
||||
|
||||
int main (int argc, char **argv)
|
||||
{
|
||||
int main (int argc, char **argv)
|
||||
{
|
||||
pthread_t thread;
|
||||
|
||||
printf("main thread [%ld]\n", gettid());
|
||||
@ -868,4 +885,4 @@ Appendix B. Minimal main()
|
||||
|
||||
printf("main dies [%ld]\n", gettid());
|
||||
return 0;
|
||||
}
|
||||
}
|
||||
@ -1,9 +1,10 @@
|
||||
=============
|
||||
CFS Scheduler
|
||||
=============
|
||||
=============
|
||||
CFS Scheduler
|
||||
=============
|
||||
|
||||
|
||||
1. OVERVIEW
|
||||
============
|
||||
|
||||
CFS stands for "Completely Fair Scheduler," and is the new "desktop" process
|
||||
scheduler implemented by Ingo Molnar and merged in Linux 2.6.23. It is the
|
||||
@ -27,6 +28,7 @@ is its actual runtime normalized to the total number of running tasks.
|
||||
|
||||
|
||||
2. FEW IMPLEMENTATION DETAILS
|
||||
==============================
|
||||
|
||||
In CFS the virtual runtime is expressed and tracked via the per-task
|
||||
p->se.vruntime (nanosec-unit) value. This way, it's possible to accurately
|
||||
@ -49,6 +51,7 @@ algorithm variants to recognize sleepers.
|
||||
|
||||
|
||||
3. THE RBTREE
|
||||
==============
|
||||
|
||||
CFS's design is quite radical: it does not use the old data structures for the
|
||||
runqueues, but it uses a time-ordered rbtree to build a "timeline" of future
|
||||
@ -84,6 +87,7 @@ picked and the current task is preempted.
|
||||
|
||||
|
||||
4. SOME FEATURES OF CFS
|
||||
========================
|
||||
|
||||
CFS uses nanosecond granularity accounting and does not rely on any jiffies or
|
||||
other HZ detail. Thus the CFS scheduler has no notion of "timeslices" in the
|
||||
@ -113,6 +117,7 @@ result.
|
||||
|
||||
|
||||
5. Scheduling policies
|
||||
======================
|
||||
|
||||
CFS implements three scheduling policies:
|
||||
|
||||
@ -137,6 +142,7 @@ SCHED_IDLE.
|
||||
|
||||
|
||||
6. SCHEDULING CLASSES
|
||||
======================
|
||||
|
||||
The new CFS scheduler has been designed in such a way to introduce "Scheduling
|
||||
Classes," an extensible hierarchy of scheduler modules. These modules
|
||||
@ -197,6 +203,7 @@ This is the (partial) list of the hooks:
|
||||
|
||||
|
||||
7. GROUP SCHEDULER EXTENSIONS TO CFS
|
||||
=====================================
|
||||
|
||||
Normally, the scheduler operates on individual tasks and strives to provide
|
||||
fair CPU time to each task. Sometimes, it may be desirable to group tasks and
|
||||
@ -219,7 +226,7 @@ SCHED_BATCH) tasks.
|
||||
|
||||
When CONFIG_FAIR_GROUP_SCHED is defined, a "cpu.shares" file is created for each
|
||||
group created using the pseudo filesystem. See example steps below to create
|
||||
task groups and modify their CPU share using the "cgroups" pseudo filesystem.
|
||||
task groups and modify their CPU share using the "cgroups" pseudo filesystem::
|
||||
|
||||
# mount -t tmpfs cgroup_root /sys/fs/cgroup
|
||||
# mkdir /sys/fs/cgroup/cpu
|
||||
@ -1,3 +1,7 @@
|
||||
=================
|
||||
Scheduler Domains
|
||||
=================
|
||||
|
||||
Each CPU has a "base" scheduling domain (struct sched_domain). The domain
|
||||
hierarchy is built from these base domains via the ->parent pointer. ->parent
|
||||
MUST be NULL terminated, and domain structures should be per-CPU as they are
|
||||
@ -46,7 +50,9 @@ CPU's runqueue and the newly found busiest one and starts moving tasks from it
|
||||
to our runqueue. The exact number of tasks amounts to an imbalance previously
|
||||
computed while iterating over this sched domain's groups.
|
||||
|
||||
*** Implementing sched domains ***
|
||||
Implementing sched domains
|
||||
==========================
|
||||
|
||||
The "base" domain will "span" the first level of the hierarchy. In the case
|
||||
of SMT, you'll span all siblings of the physical CPU, with each group being
|
||||
a single virtual CPU.
|
||||
@ -1,6 +1,6 @@
|
||||
=======================
|
||||
Energy Aware Scheduling
|
||||
=======================
|
||||
=======================
|
||||
Energy Aware Scheduling
|
||||
=======================
|
||||
|
||||
1. Introduction
|
||||
---------------
|
||||
@ -12,7 +12,7 @@ with a minimal impact on throughput. This document aims at providing an
|
||||
introduction on how EAS works, what are the main design decisions behind it, and
|
||||
details what is needed to get it to run.
|
||||
|
||||
Before going any further, please note that at the time of writing:
|
||||
Before going any further, please note that at the time of writing::
|
||||
|
||||
/!\ EAS does not support platforms with symmetric CPU topologies /!\
|
||||
|
||||
@ -33,13 +33,13 @@ To make it clear from the start:
|
||||
- power = energy/time = [joule/second] = [watt]
|
||||
|
||||
The goal of EAS is to minimize energy, while still getting the job done. That
|
||||
is, we want to maximize:
|
||||
is, we want to maximize::
|
||||
|
||||
performance [inst/s]
|
||||
--------------------
|
||||
power [W]
|
||||
|
||||
which is equivalent to minimizing:
|
||||
which is equivalent to minimizing::
|
||||
|
||||
energy [J]
|
||||
-----------
|
||||
@ -97,7 +97,7 @@ domains can contain duplicate elements.
|
||||
|
||||
Example 1.
|
||||
Let us consider a platform with 12 CPUs, split in 3 performance domains
|
||||
(pd0, pd4 and pd8), organized as follows:
|
||||
(pd0, pd4 and pd8), organized as follows::
|
||||
|
||||
CPUs: 0 1 2 3 4 5 6 7 8 9 10 11
|
||||
PDs: |--pd0--|--pd4--|---pd8---|
|
||||
@ -108,6 +108,7 @@ Example 1.
|
||||
containing 6 CPUs. The two root domains are denoted rd1 and rd2 in the
|
||||
above figure. Since pd4 intersects with both rd1 and rd2, it will be
|
||||
present in the linked list '->pd' attached to each of them:
|
||||
|
||||
* rd1->pd: pd0 -> pd4
|
||||
* rd2->pd: pd4 -> pd8
|
||||
|
||||
@ -159,9 +160,9 @@ Example 2.
|
||||
Each performance domain has three Operating Performance Points (OPPs).
|
||||
The CPU capacity and power cost associated with each OPP is listed in
|
||||
the Energy Model table. The util_avg of P is shown on the figures
|
||||
below as 'PP'.
|
||||
below as 'PP'::
|
||||
|
||||
CPU util.
|
||||
CPU util.
|
||||
1024 - - - - - - - Energy Model
|
||||
+-----------+-------------+
|
||||
| Little | Big |
|
||||
@ -188,8 +189,7 @@ Example 2.
|
||||
(which is coherent with the behaviour of the schedutil CPUFreq
|
||||
governor, see Section 6. for more details on this topic).
|
||||
|
||||
Case 1. P is migrated to CPU1
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
**Case 1. P is migrated to CPU1**::
|
||||
|
||||
1024 - - - - - - -
|
||||
|
||||
@ -207,8 +207,7 @@ Example 2.
|
||||
CPU0 CPU1 CPU2 CPU3
|
||||
|
||||
|
||||
Case 2. P is migrated to CPU3
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
**Case 2. P is migrated to CPU3**::
|
||||
|
||||
1024 - - - - - - -
|
||||
|
||||
@ -226,8 +225,7 @@ Example 2.
|
||||
CPU0 CPU1 CPU2 CPU3
|
||||
|
||||
|
||||
Case 3. P stays on prev_cpu / CPU 0
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
**Case 3. P stays on prev_cpu / CPU 0**::
|
||||
|
||||
1024 - - - - - - -
|
||||
|
||||
@ -324,7 +322,9 @@ hardware properties and on other features of the kernel being enabled. This
|
||||
section lists these dependencies and provides hints as to how they can be met.
|
||||
|
||||
|
||||
6.1 - Asymmetric CPU topology
|
||||
6.1 - Asymmetric CPU topology
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
|
||||
As mentioned in the introduction, EAS is only supported on platforms with
|
||||
asymmetric CPU topologies for now. This requirement is checked at run-time by
|
||||
@ -347,7 +347,8 @@ significant savings on SMP platforms have been observed yet. This restriction
|
||||
could be amended in the future if proven otherwise.
|
||||
|
||||
|
||||
6.2 - Energy Model presence
|
||||
6.2 - Energy Model presence
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
EAS uses the EM of a platform to estimate the impact of scheduling decisions on
|
||||
energy. So, your platform must provide power cost tables to the EM framework in
|
||||
@ -358,7 +359,8 @@ Please also note that the scheduling domains need to be re-built after the
|
||||
EM has been registered in order to start EAS.
|
||||
|
||||
|
||||
6.3 - Energy Model complexity
|
||||
6.3 - Energy Model complexity
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
The task wake-up path is very latency-sensitive. When the EM of a platform is
|
||||
too complex (too many CPUs, too many performance domains, too many performance
|
||||
@ -388,7 +390,8 @@ two possible options:
|
||||
hence enabling it to cope with larger EMs in reasonable time.
|
||||
|
||||
|
||||
6.4 - Schedutil governor
|
||||
6.4 - Schedutil governor
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
EAS tries to predict at which OPP will the CPUs be running in the close future
|
||||
in order to estimate their energy consumption. To do so, it is assumed that OPPs
|
||||
@ -405,7 +408,8 @@ frequency requests and energy predictions.
|
||||
Using EAS with any other governor than schedutil is not supported.
|
||||
|
||||
|
||||
6.5 Scale-invariant utilization signals
|
||||
6.5 Scale-invariant utilization signals
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
In order to make accurate prediction across CPUs and for all performance
|
||||
states, EAS needs frequency-invariant and CPU-invariant PELT signals. These can
|
||||
@ -416,7 +420,8 @@ Using EAS on a platform that doesn't implement these two callbacks is not
|
||||
supported.
|
||||
|
||||
|
||||
6.6 Multithreading (SMT)
|
||||
6.6 Multithreading (SMT)
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
EAS in its current form is SMT unaware and is not able to leverage
|
||||
multithreaded hardware to save energy. EAS considers threads as independent
|
||||
@ -1,3 +1,7 @@
|
||||
=====================
|
||||
Scheduler Nice Design
|
||||
=====================
|
||||
|
||||
This document explains the thinking about the revamped and streamlined
|
||||
nice-levels implementation in the new Linux scheduler.
|
||||
|
||||
@ -14,7 +18,7 @@ much stronger than they were before in 2.4 (and people were happy about
|
||||
that change), and we also intentionally calibrated the linear timeslice
|
||||
rule so that nice +19 level would be _exactly_ 1 jiffy. To better
|
||||
understand it, the timeslice graph went like this (cheesy ASCII art
|
||||
alert!):
|
||||
alert!)::
|
||||
|
||||
|
||||
A
|
||||
@ -1,18 +1,18 @@
|
||||
Real-Time group scheduling
|
||||
--------------------------
|
||||
==========================
|
||||
Real-Time group scheduling
|
||||
==========================
|
||||
|
||||
CONTENTS
|
||||
========
|
||||
.. CONTENTS
|
||||
|
||||
0. WARNING
|
||||
1. Overview
|
||||
1.1 The problem
|
||||
1.2 The solution
|
||||
2. The interface
|
||||
2.1 System-wide settings
|
||||
2.2 Default behaviour
|
||||
2.3 Basis for grouping tasks
|
||||
3. Future plans
|
||||
0. WARNING
|
||||
1. Overview
|
||||
1.1 The problem
|
||||
1.2 The solution
|
||||
2. The interface
|
||||
2.1 System-wide settings
|
||||
2.2 Default behaviour
|
||||
2.3 Basis for grouping tasks
|
||||
3. Future plans
|
||||
|
||||
|
||||
0. WARNING
|
||||
@ -159,9 +159,11 @@ Consider two sibling groups A and B; both have 50% bandwidth, but A's
|
||||
period is twice the length of B's.
|
||||
|
||||
* group A: period=100000us, runtime=50000us
|
||||
|
||||
- this runs for 0.05s once every 0.1s
|
||||
|
||||
* group B: period= 50000us, runtime=25000us
|
||||
|
||||
- this runs for 0.025s twice every 0.1s (or once every 0.05 sec).
|
||||
|
||||
This means that currently a while (1) loop in A will run for the full period of
|
||||
@ -1,3 +1,7 @@
|
||||
====================
|
||||
Scheduler Statistics
|
||||
====================
|
||||
|
||||
Version 15 of schedstats dropped counters for some sched_yield:
|
||||
yld_exp_empty, yld_act_empty and yld_both_empty. Otherwise, it is
|
||||
identical to version 14.
|
||||
@ -35,19 +39,23 @@ CPU statistics
|
||||
cpu<N> 1 2 3 4 5 6 7 8 9
|
||||
|
||||
First field is a sched_yield() statistic:
|
||||
|
||||
1) # of times sched_yield() was called
|
||||
|
||||
Next three are schedule() statistics:
|
||||
|
||||
2) This field is a legacy array expiration count field used in the O(1)
|
||||
scheduler. We kept it for ABI compatibility, but it is always set to zero.
|
||||
3) # of times schedule() was called
|
||||
4) # of times schedule() left the processor idle
|
||||
|
||||
Next two are try_to_wake_up() statistics:
|
||||
|
||||
5) # of times try_to_wake_up() was called
|
||||
6) # of times try_to_wake_up() was called to wake up the local cpu
|
||||
|
||||
Next three are statistics describing scheduling latency:
|
||||
|
||||
7) sum of all time spent running by tasks on this processor (in jiffies)
|
||||
8) sum of all time spent waiting to run by tasks on this processor (in
|
||||
jiffies)
|
||||
@ -67,24 +75,23 @@ The first field is a bit mask indicating what cpus this domain operates over.
|
||||
The next 24 are a variety of load_balance() statistics in grouped into types
|
||||
of idleness (idle, busy, and newly idle):
|
||||
|
||||
1) # of times in this domain load_balance() was called when the
|
||||
1) # of times in this domain load_balance() was called when the
|
||||
cpu was idle
|
||||
2) # of times in this domain load_balance() checked but found
|
||||
2) # of times in this domain load_balance() checked but found
|
||||
the load did not require balancing when the cpu was idle
|
||||
3) # of times in this domain load_balance() tried to move one or
|
||||
3) # of times in this domain load_balance() tried to move one or
|
||||
more tasks and failed, when the cpu was idle
|
||||
4) sum of imbalances discovered (if any) with each call to
|
||||
4) sum of imbalances discovered (if any) with each call to
|
||||
load_balance() in this domain when the cpu was idle
|
||||
5) # of times in this domain pull_task() was called when the cpu
|
||||
5) # of times in this domain pull_task() was called when the cpu
|
||||
was idle
|
||||
6) # of times in this domain pull_task() was called even though
|
||||
6) # of times in this domain pull_task() was called even though
|
||||
the target task was cache-hot when idle
|
||||
7) # of times in this domain load_balance() was called but did
|
||||
7) # of times in this domain load_balance() was called but did
|
||||
not find a busier queue while the cpu was idle
|
||||
8) # of times in this domain a busier queue was found while the
|
||||
8) # of times in this domain a busier queue was found while the
|
||||
cpu was idle but no busier group was found
|
||||
|
||||
9) # of times in this domain load_balance() was called when the
|
||||
9) # of times in this domain load_balance() was called when the
|
||||
cpu was busy
|
||||
10) # of times in this domain load_balance() checked but found the
|
||||
load did not require balancing when busy
|
||||
@ -117,21 +124,25 @@ of idleness (idle, busy, and newly idle):
|
||||
was just becoming idle but no busier group was found
|
||||
|
||||
Next three are active_load_balance() statistics:
|
||||
|
||||
25) # of times active_load_balance() was called
|
||||
26) # of times active_load_balance() tried to move a task and failed
|
||||
27) # of times active_load_balance() successfully moved a task
|
||||
|
||||
Next three are sched_balance_exec() statistics:
|
||||
|
||||
28) sbe_cnt is not used
|
||||
29) sbe_balanced is not used
|
||||
30) sbe_pushed is not used
|
||||
|
||||
Next three are sched_balance_fork() statistics:
|
||||
|
||||
31) sbf_cnt is not used
|
||||
32) sbf_balanced is not used
|
||||
33) sbf_pushed is not used
|
||||
|
||||
Next three are try_to_wake_up() statistics:
|
||||
|
||||
34) # of times in this domain try_to_wake_up() awoke a task that
|
||||
last ran on a different cpu in this domain
|
||||
35) # of times in this domain try_to_wake_up() moved a task to the
|
||||
@ -139,10 +150,11 @@ of idleness (idle, busy, and newly idle):
|
||||
36) # of times in this domain try_to_wake_up() started passive balancing
|
||||
|
||||
/proc/<pid>/schedstat
|
||||
----------------
|
||||
---------------------
|
||||
schedstats also adds a new /proc/<pid>/schedstat file to include some of
|
||||
the same information on a per-process level. There are three fields in
|
||||
this file correlating for that process to:
|
||||
|
||||
1) time spent on the cpu
|
||||
2) time spent waiting on a runqueue
|
||||
3) # of timeslices run on this cpu
|
||||
@ -151,4 +163,5 @@ A program could be easily written to make use of these extra fields to
|
||||
report on how well a particular process or set of processes is faring
|
||||
under the scheduler's policies. A simple version of such a program is
|
||||
available at
|
||||
|
||||
http://eaglet.rain.com/rick/linux/schedstat/v12/latency.c
|
||||
5
Documentation/scheduler/text_files.rst
Normal file
5
Documentation/scheduler/text_files.rst
Normal file
@ -0,0 +1,5 @@
|
||||
Scheduler pelt c program
|
||||
------------------------
|
||||
|
||||
.. literalinclude:: sched-pelt.c
|
||||
:language: c
|
||||
@ -99,7 +99,7 @@ Local allocation will tend to keep subsequent access to the allocated memory
|
||||
as long as the task on whose behalf the kernel allocated some memory does not
|
||||
later migrate away from that memory. The Linux scheduler is aware of the
|
||||
NUMA topology of the platform--embodied in the "scheduling domains" data
|
||||
structures [see Documentation/scheduler/sched-domains.txt]--and the scheduler
|
||||
structures [see Documentation/scheduler/sched-domains.rst]--and the scheduler
|
||||
attempts to minimize task migration to distant scheduling domains. However,
|
||||
the scheduler does not take a task's NUMA footprint into account directly.
|
||||
Thus, under sufficient imbalance, tasks can migrate between nodes, remote
|
||||
|
||||
@ -734,7 +734,7 @@ menuconfig CGROUPS
|
||||
use with process control subsystems such as Cpusets, CFS, memory
|
||||
controls or device isolation.
|
||||
See
|
||||
- Documentation/scheduler/sched-design-CFS.txt (CFS)
|
||||
- Documentation/scheduler/sched-design-CFS.rst (CFS)
|
||||
- Documentation/cgroup-v1/ (features for grouping, isolation
|
||||
and resource control)
|
||||
|
||||
@ -835,7 +835,7 @@ config CFS_BANDWIDTH
|
||||
tasks running within the fair group scheduler. Groups with no limit
|
||||
set are considered to be unconstrained and will run with no
|
||||
restriction.
|
||||
See Documentation/scheduler/sched-bwc.txt for more information.
|
||||
See Documentation/scheduler/sched-bwc.rst for more information.
|
||||
|
||||
config RT_GROUP_SCHED
|
||||
bool "Group scheduling for SCHED_RR/FIFO"
|
||||
@ -846,7 +846,7 @@ config RT_GROUP_SCHED
|
||||
to task groups. If enabled, it will also make it impossible to
|
||||
schedule realtime tasks for non-root users until you allocate
|
||||
realtime bandwidth for them.
|
||||
See Documentation/scheduler/sched-rt-group.txt for more information.
|
||||
See Documentation/scheduler/sched-rt-group.rst for more information.
|
||||
|
||||
endif #CGROUP_SCHED
|
||||
|
||||
|
||||
@ -726,7 +726,7 @@ static void replenish_dl_entity(struct sched_dl_entity *dl_se,
|
||||
* refill the runtime and set the deadline a period in the future,
|
||||
* because keeping the current (absolute) deadline of the task would
|
||||
* result in breaking guarantees promised to other tasks (refer to
|
||||
* Documentation/scheduler/sched-deadline.txt for more information).
|
||||
* Documentation/scheduler/sched-deadline.rst for more information).
|
||||
*
|
||||
* This function returns true if:
|
||||
*
|
||||
|
||||
Loading…
Reference in New Issue
Block a user