Introduce the use cases of delay max, which can help quickly detect
potential abnormal delays in the system and record the types and specific
details of delay spikes.
Problem
========
Delay accounting can track the average delay of processes to show
system workload. However, when a process experiences a significant
delay, maybe a delay spike, which adversely affects performance,
getdelays can only display the average system delay over a period
of time. Yet, average delay is unhelpful for diagnosing delay peak.
It is not even possible to determine which type of delay has spiked,
as this information might be masked by the average delay.
Solution
=========
the 'delay max' can display delay peak since the system's startup,
which can record potential abnormal delays over time, including
the type of delay and the maximum delay. This is helpful for
quickly identifying crash caused by delay.
Use case
=========
bash# ./getdelays -d -p 244
print delayacct stats ON
PID 244
CPU count real total virtual total delay total delay average delay max
68 192000000 213676651 705643 0.010ms 0.306381ms
IO count delay total delay average delay max
0 0 0.000ms 0.000000ms
SWAP count delay total delay average delay max
0 0 0.000ms 0.000000ms
RECLAIM count delay total delay average delay max
0 0 0.000ms 0.000000ms
THRASHING count delay total delay average delay max
0 0 0.000ms 0.000000ms
COMPACT count delay total delay average delay max
0 0 0.000ms 0.000000ms
WPCOPY count delay total delay average delay max
235 15648284 0.067ms 0.263842ms
IRQ count delay total delay average delay max
0 0 0.000ms 0.000000ms
Link: https://lkml.kernel.org/r/20241203164848805CS62CQPQWG9GLdQj2_BxS@zte.com.cn
Co-developed-by: Wang Yong <wang.yong12@zte.com.cn>
Signed-off-by: Wang Yong <wang.yong12@zte.com.cn>
Co-developed-by: xu xin <xu.xin16@zte.com.cn>
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Co-developed-by: Wang Yaxin <wang.yaxin@zte.com.cn>
Signed-off-by: Wang Yaxin <wang.yaxin@zte.com.cn>
Signed-off-by: Kun Jiang <jiang.kun2@zte.com.cn>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Fan Yu <fan.yu9@zte.com.cn>
Cc: Peilin He <he.peilin@zte.com.cn>
Cc: tuqiang <tu.qiang35@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: ye xingchen <ye.xingchen@zte.com.cn>
Cc: Yunkai Zhang <zhang.yunkai@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
CPU unplug first calls __cpu_disable(), and that's where powerpc calls
cleanup_cpu_mmu_context(), which clears this CPU from mm_cpumask() of all
mms in the system.
However this CPU may still be using a lazy tlb mm, and its mm_cpumask bit
will be cleared from it. The CPU does not switch away from the lazy tlb
mm until arch_cpu_idle_dead() calls idle_task_exit().
If that user mm exits in this window, it will not be subject to the lazy
tlb mm shootdown and may be freed while in use as a lazy mm by the CPU
that is being unplugged.
cleanup_cpu_mmu_context() could be moved later, but it looks better to
move the lazy tlb mm switching earlier. The problem with doing the lazy
mm switching in idle_task_exit() is explained in commit bf2c59fce4
("sched/core: Fix illegal RCU from offline CPUs"), which added a wart to
switch away from the mm but leave it set in active_mm to be cleaned up
later.
So instead, switch away from the lazy tlb mm at sched_cpu_wait_empty(),
which is the last hotplug state before teardown
(CPUHP_AP_SCHED_WAIT_EMPTY). This CPU will never switch to a user thread
from this point, so it has no chance to pick up a new lazy tlb mm. This
removes the lazy tlb mm handling wart in CPU unplug.
With this, idle_task_exit() is not needed anymore and can be cleaned up.
This leaves the prototype alone, to be cleaned after this change.
herton: took the suggestions from https://lore.kernel.org/all/87jzvyprsw.ffs@tglx/
and made adjustments on the initial patch proposed by Nicholas.
Link: https://lkml.kernel.org/r/20230524060455.147699-1-npiggin@gmail.com
Link: https://lore.kernel.org/all/20230525205253.E2FAEC433EF@smtp.kernel.org/
Link: https://lkml.kernel.org/r/20241104142318.3295663-1-herton@redhat.com
Fixes: 2655421ae6 ("lazy tlb: shoot lazies, non-refcounting lazy tlb mm reference handling scheme")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Herton R. Krzesinski <herton@redhat.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
kasan_record_aux_stack_noalloc() was introduced to record a stack trace
without allocating memory in the process. It has been added to callers
which were invoked while a raw_spinlock_t was held. More and more callers
were identified and changed over time. Is it a good thing to have this
while functions try their best to do a locklessly setup? The only
downside of having kasan_record_aux_stack() not allocate any memory is
that we end up without a stacktrace if stackdepot runs out of memory and
at the same stacktrace was not recorded before To quote Marco Elver from
https://lore.kernel.org/all/CANpmjNPmQYJ7pv1N3cuU8cP18u7PP_uoZD8YxwZd4jtbof9nVQ@mail.gmail.com/
| I'd be in favor, it simplifies things. And stack depot should be
| able to replenish its pool sufficiently in the "non-aux" cases
| i.e. regular allocations. Worst case we fail to record some
| aux stacks, but I think that's only really bad if there's a bug
| around one of these allocations. In general the probabilities
| of this being a regression are extremely small [...]
Make the kasan_record_aux_stack_noalloc() behaviour default as
kasan_record_aux_stack().
[bigeasy@linutronix.de: dressed the diff as patch]
Link: https://lkml.kernel.org/r/20241122155451.Mb2pmeyJ@linutronix.de
Fixes: 7cb3007ce2 ("kasan: generic: introduce kasan_record_aux_stack_noalloc()")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reported-by: syzbot+39f85d612b7c20d8db48@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/67275485.050a0220.3c8d68.0a37.GAE@google.com
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: <kasan-dev@googlegroups.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: syzkaller-bugs@googlegroups.com
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zqiang <qiang.zhang1211@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Function sugov_eas_rebuild_sd() defined in the schedutil cpufreq governor
implements generic functionality that may be useful in other places. In
particular, there is a plan to use it in the intel_pstate driver in the
future.
For this reason, move it from schedutil to the energy model code and
rename it to em_rebuild_sched_domains().
This also helps to get rid of some #ifdeffery in schedutil which is a
plus.
No intentional functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
A redundant frequency update is only truly needed when there is a policy
limits change with a driver that specifies CPUFREQ_NEED_UPDATE_LIMITS.
In spite of that, drivers specifying CPUFREQ_NEED_UPDATE_LIMITS receive a
frequency update _all the time_, not just for a policy limits change,
because need_freq_update is never cleared.
Furthermore, ignore_dl_rate_limit()'s usage of need_freq_update also leads
to a redundant frequency update, regardless of whether or not the driver
specifies CPUFREQ_NEED_UPDATE_LIMITS, when the next chosen frequency is the
same as the current one.
Fix the superfluous updates by only honoring CPUFREQ_NEED_UPDATE_LIMITS
when there's a policy limits change, and clearing need_freq_update when a
requisite redundant update occurs.
This is neatly achieved by moving up the CPUFREQ_NEED_UPDATE_LIMITS test
and instead setting need_freq_update to false in sugov_update_next_freq().
Fixes: 600f5badb7 ("cpufreq: schedutil: Don't skip freq update when limits change")
Signed-off-by: Sultan Alsawaf (unemployed) <sultan@kerneltoast.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20241212015734.41241-2-sultan@kerneltoast.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
CPU controller limits are not properly enforced during CPU hotplug
operations, particularly during CPU offline. When a CPU goes offline,
throttled processes are unintentionally being unthrottled across all CPUs
in the system, allowing them to exceed their assigned quota limits.
Consider below for an example,
Assigning 6.25% bandwidth limit to a cgroup
in a 8 CPU system, where, workload is running 8 threads for 20 seconds at
100% CPU utilization, expected (user+sys) time = 10 seconds.
$ cat /sys/fs/cgroup/test/cpu.max
50000 100000
$ ./ebizzy -t 8 -S 20 // non-hotplug case
real 20.00 s
user 10.81 s // intended behaviour
sys 0.00 s
$ ./ebizzy -t 8 -S 20 // hotplug case
real 20.00 s
user 14.43 s // Workload is able to run for 14 secs
sys 0.00 s // when it should have only run for 10 secs
During CPU hotplug, scheduler domains are rebuilt and cpu_attach_domain
is called for every active CPU to update the root domain. That ends up
calling rq_offline_fair which un-throttles any throttled hierarchies.
Unthrottling should only occur for the CPU being hotplugged to allow its
throttled processes to become runnable and get migrated to other CPUs.
With current patch applied,
$ ./ebizzy -t 8 -S 20 // hotplug case
real 21.00 s
user 10.16 s // intended behaviour
sys 0.00 s
This also has another symptom, when a CPU goes offline, and if the cfs_rq
is not in throttled state and the runtime_remaining still had plenty
remaining, it gets reset to 1 here, causing the runtime_remaining of
cfs_rq to be quickly depleted.
Note: hotplug operation (online, offline) was performed in while(1) loop
v3: https://lore.kernel.org/all/20241210102346.228663-2-vishalc@linux.ibm.com
v2: https://lore.kernel.org/all/20241207052730.1746380-2-vishalc@linux.ibm.com
v1: https://lore.kernel.org/all/20241126064812.809903-2-vishalc@linux.ibm.com
Suggested-by: Zhang Qiao <zhangqiao22@huawei.com>
Signed-off-by: Vishal Chourasia <vishalc@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Tested-by: Samir Mulani <samir@linux.ibm.com>
Link: https://lore.kernel.org/r/20241212043102.584863-2-vishalc@linux.ibm.com
kthread_create() creates a kthread without running it yet. kthread_run()
creates a kthread and runs it.
On the other hand, kthread_create_worker() creates a kthread worker and
runs it.
This difference in behaviours is confusing. Also there is no way to
create a kthread worker and affine it using kthread_bind_mask() or
kthread_affine_preferred() before starting it.
Consolidate the behaviours and introduce kthread_run_worker[_on_cpu]()
that behaves just like kthread_run(). kthread_create_worker[_on_cpu]()
will now only create a kthread worker without starting it.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
When a kthread or any other task has an affinity mask that is fully
offline or unallowed, the scheduler reaffines the task to all possible
CPUs as a last resort.
This default decision doesn't mix up very well with nohz_full CPUs that
are part of the possible cpumask but don't want to be disturbed by
unbound kthreads or even detached pinned user tasks.
Make the fallback affinity setting aware of nohz_full.
Suggested-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
its time accounting
- Properly track the CFS runqueue runnable stats
- Check the total number of all queued tasks in a sched fair's runqueue
hierarchy before deciding to stop the tick
- Fix the scheduling of the task that got woken last (NEXT_BUDDY) by
preventing those from being delayed
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Merge tag 'sched_urgent_for_v6.13_rc3-p2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler fixes from Borislav Petkov:
- Prevent incorrect dequeueing of the deadline dlserver helper task and
fix its time accounting
- Properly track the CFS runqueue runnable stats
- Check the total number of all queued tasks in a sched fair's runqueue
hierarchy before deciding to stop the tick
- Fix the scheduling of the task that got woken last (NEXT_BUDDY) by
preventing those from being delayed
* tag 'sched_urgent_for_v6.13_rc3-p2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/dlserver: Fix dlserver time accounting
sched/dlserver: Fix dlserver double enqueue
sched/eevdf: More PELT vs DELAYED_DEQUEUE
sched/fair: Fix sched_can_stop_tick() for fair tasks
sched/fair: Fix NEXT_BUDDY
Update the `dsq_hash_params` initialization to use `sizeof_field`
for the `key_len` field instead of a hardcoded value.
This improves code readability and ensures the key length dynamically
matches the size of the `id` field in the `scx_dispatch_q` structure.
Signed-off-by: Liang Jie <liangjie@lixiang.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
dlserver time is accounted when:
- dlserver is active and the dlserver proxies the cfs task.
- dlserver is active but deferred and cfs task runs after being picked
through the normal fair class pick.
dl_server_update is called in two places to make sure that both the
above times are accounted for. But it doesn't check if dlserver is
active or not. Now that we have this dl_server_active flag, we can
consolidate dl_server_update into one place and all we need to check is
whether dlserver is active or not. When dlserver is active there is only
two possible conditions:
- dlserver is deferred.
- cfs task is running on behalf of dlserver.
Fixes: a110a81c52 ("sched/deadline: Deferrable dl server")
Signed-off-by: "Vineeth Pillai (Google)" <vineeth@bitbyteword.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Marcel Ziswiler <marcel.ziswiler@codethink.co.uk> # ROCK 5B
Link: https://lore.kernel.org/r/20241213032244.877029-2-vineeth@bitbyteword.org
dlserver can get dequeued during a dlserver pick_task due to the delayed
deueue feature and this can lead to issues with dlserver logic as it
still thinks that dlserver is on the runqueue. The dlserver throttling
and replenish logic gets confused and can lead to double enqueue of
dlserver.
Double enqueue of dlserver could happend due to couple of reasons:
Case 1
------
Delayed dequeue feature[1] can cause dlserver being stopped during a
pick initiated by dlserver:
__pick_next_task
pick_task_dl -> server_pick_task
pick_task_fair
pick_next_entity (if (sched_delayed))
dequeue_entities
dl_server_stop
server_pick_task goes ahead with update_curr_dl_se without knowing that
dlserver is dequeued and this confuses the logic and may lead to
unintended enqueue while the server is stopped.
Case 2
------
A race condition between a task dequeue on one cpu and same task's enqueue
on this cpu by a remote cpu while the lock is released causing dlserver
double enqueue.
One cpu would be in the schedule() and releasing RQ-lock:
current->state = TASK_INTERRUPTIBLE();
schedule();
deactivate_task()
dl_stop_server();
pick_next_task()
pick_next_task_fair()
sched_balance_newidle()
rq_unlock(this_rq)
at which point another CPU can take our RQ-lock and do:
try_to_wake_up()
ttwu_queue()
rq_lock()
...
activate_task()
dl_server_start() --> first enqueue
wakeup_preempt() := check_preempt_wakeup_fair()
update_curr()
update_curr_task()
if (current->dl_server)
dl_server_update()
enqueue_dl_entity() --> second enqueue
This bug was not apparent as the enqueue in dl_server_start doesn't
usually happen because of the defer logic. But as a side effect of the
first case(dequeue during dlserver pick), dl_throttled and dl_yield will
be set and this causes the time accounting of dlserver to messup and
then leading to a enqueue in dl_server_start.
Have an explicit flag representing the status of dlserver to avoid the
confusion. This is set in dl_server_start and reset in dlserver_stop.
Fixes: 63ba8422f8 ("sched/deadline: Introduce deadline servers")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: "Vineeth Pillai (Google)" <vineeth@bitbyteword.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Marcel Ziswiler <marcel.ziswiler@codethink.co.uk> # ROCK 5B
Link: https://lkml.kernel.org/r/20241213032244.877029-1-vineeth@bitbyteword.org
Commit 8b5e770ed7 ("sched/deadline: Optimize pull_dl_task()")
added a goto label seems would be better written as a while
loop.
So replace the goto with a while loop, to make it easier to read.
Reported-by: Todd Kjos <tkjos@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
Reviewed-and-tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lore.kernel.org/r/20241206000009.1226085-1-jstultz@google.com
a RT mutex
- Do not setup a new deadline entity on a boosted task as that has happened
already
- Update preempt= kernel command line param
- Prevent needless softirqd wakeups in the idle task's context
- Detect the case where the idle load balancer CPU becomes busy and avoid
unnecessary load balancing invocation
- Remove an unnecessary load balancing need_resched() call in nohz_csd_func()
- Allow for raising of SCHED_SOFTIRQ softirq type on RT but retain the warning
to catch any other cases
- Remove a wrong warning when a cpuset update makes the task affinity no
longer a subset of the cpuset
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Merge tag 'sched_urgent_for_v6.13_rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler fixes from Borislav Petkov:
- Remove wrong enqueueing of a task for a later wakeup when a task
blocks on a RT mutex
- Do not setup a new deadline entity on a boosted task as that has
happened already
- Update preempt= kernel command line param
- Prevent needless softirqd wakeups in the idle task's context
- Detect the case where the idle load balancer CPU becomes busy and
avoid unnecessary load balancing invocation
- Remove an unnecessary load balancing need_resched() call in
nohz_csd_func()
- Allow for raising of SCHED_SOFTIRQ softirq type on RT but retain the
warning to catch any other cases
- Remove a wrong warning when a cpuset update makes the task affinity
no longer a subset of the cpuset
* tag 'sched_urgent_for_v6.13_rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
locking: rtmutex: Fix wake_q logic in task_blocks_on_rt_mutex
sched/deadline: Fix warning in migrate_enable for boosted tasks
sched/core: Update kernel boot parameters for LAZY preempt.
sched/core: Prevent wakeup of ksoftirqd during idle load balance
sched/fair: Check idle_cpu() before need_resched() to detect ilb CPU turning busy
sched/core: Remove the unnecessary need_resched() check in nohz_csd_func()
softirq: Allow raising SCHED_SOFTIRQ from SMP-call-function on RT kernel
sched: fix warning in sched_setaffinity
sched/deadline: Fix replenish_dl_new_period dl_server condition
There are 3 sites using set_next_buddy() and only one is conditional
on NEXT_BUDDY, the other two sites are unconditional; to note:
- yield_to_task()
- cgroup dequeue / pick optimization
However, having NEXT_BUDDY control both the wakeup-preemption and the
picking side of things means its near useless.
Fixes: 147f3efaa2 ("sched/fair: Implement an EEVDF-like scheduling policy")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20241129101541.GA33464@noisy.programming.kicks-ass.net
When max_vruntime() is unused, it prevents kernel builds with clang,
`make W=1` and CONFIG_WERROR=y:
kernel/sched/fair.c:526:19: error: unused function 'max_vruntime' [-Werror,-Wunused-function]
526 | static inline u64 max_vruntime(u64 max_vruntime, u64 vruntime)
| ^~~~~~~~~~~~
Fix this by marking them with __maybe_unused (all cases for the sake of
symmetry).
See also commit 6863f5643d ("kbuild: allow Clang to find unused static
inline functions for W=1 build").
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20241202173546.634433-1-andriy.shevchenko@linux.intel.com
Move variable declaration at the beginning of the function
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20241202174606.4074512-12-vincent.guittot@linaro.org
Migrating a delayed dequeued task doesn't help in balancing the number
of runnable tasks in the system.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20241202174606.4074512-11-vincent.guittot@linaro.org
Rename cfs_rq.nr_running into cfs_rq.nr_queued which better reflects the
reality as the value includes both the ready to run tasks and the delayed
dequeue tasks.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20241202174606.4074512-10-vincent.guittot@linaro.org
cfs_rq.idle_nr_running field is not used anywhere so we can remove the
useless associated computation. Last user went in commit 5e963f2bd4
("sched/fair: Commit to EEVDF").
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20241202174606.4074512-9-vincent.guittot@linaro.org
Use same naming convention as others starting with h_nr_* and rename
idle_h_nr_running into h_nr_idle.
The "running" is not correct anymore as it includes delayed dequeue tasks
as well.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20241202174606.4074512-8-vincent.guittot@linaro.org
h_nr_delayed is not used anymore. We now have:
- h_nr_runnable which tracks tasks ready to run
- h_nr_queued which tracks enqueued tasks either ready to run or
delayed dequeue
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20241202174606.4074512-7-vincent.guittot@linaro.org
Use the new h_nr_runnable that tracks only queued and runnable tasks in the
statistics that are used to balance the system:
- PELT runnable_avg
- deciding if a group is overloaded or has spare capacity
- numa stats
- reduced capacity management
- load balance
- nohz kick
It should be noticed that the rq->nr_running still counts the delayed
dequeued tasks as delayed dequeue is a fair feature that is meaningless
at core level.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20241202174606.4074512-6-vincent.guittot@linaro.org
With delayed dequeued feature, a sleeping sched_entity remains queued in
the rq until its lag has elapsed. As a result, it stays also visible
in the statistics that are used to balance the system and in particular
the field cfs.h_nr_queued when the sched_entity is associated to a task.
Create a new h_nr_runnable that tracks only queued and runnable tasks.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20241202174606.4074512-5-vincent.guittot@linaro.org
With delayed dequeued feature, a sleeping sched_entity remains queued
in the rq until its lag has elapsed but can't run.
Rename h_nr_running into h_nr_queued to reflect this new behavior.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20241202174606.4074512-4-vincent.guittot@linaro.org
Vincent and Dietmar noted that while
commit fc1892becd ("sched/eevdf: Fixup PELT vs DELAYED_DEQUEUE") fixes
the entity runnable stats, it does not adjust the cfs_rq runnable stats,
which are based off of h_nr_running.
Track h_nr_delayed such that we can discount those and adjust the
signal.
Fixes: fc1892becd ("sched/eevdf: Fixup PELT vs DELAYED_DEQUEUE")
Closes: https://lore.kernel.org/lkml/a9a45193-d0c6-4ba2-a822-464ad30b550e@arm.com/
Closes: https://lore.kernel.org/lkml/CAKfTPtCNUvWE_GX5LyvTF-WdxUT=ZgvZZv-4t=eWntg5uOFqiQ@mail.gmail.com/
[ Fixes checkpatch warnings and rebased ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reported-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lore.kernel.org/r/20241202174606.4074512-3-vincent.guittot@linaro.org
We can't stop the tick of a rq if there are at least 2 tasks enqueued in
the whole hierarchy and not only at the root cfs rq.
rq->cfs.nr_running tracks the number of sched_entity at one level
whereas rq->cfs.h_nr_running tracks all queued tasks in the
hierarchy.
Fixes: 11cc374f46 ("sched_ext: Simplify scx_can_stop_tick() invocation in sched_can_stop_tick()")
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20241202174606.4074512-2-vincent.guittot@linaro.org
Adam reports that enabling NEXT_BUDDY insta triggers a WARN in
pick_next_entity().
Moving clear_buddies() up before the delayed dequeue bits ensures
no ->next buddy becomes delayed. Further ensure no new ->next buddy
ever starts as delayed.
Fixes: 152e11f6df ("sched/fair: Implement delayed dequeue")
Reported-by: Adam Li <adamli@os.amperecomputing.com>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Adam Li <adamli@os.amperecomputing.com>
Link: https://lkml.kernel.org/r/670a0d54-e398-4b1f-8a6e-90784e2fdf89@amd.com
[Problem Description]
When running the hackbench program of LTP, the following memory leak is
reported by kmemleak.
# /opt/ltp/testcases/bin/hackbench 20 thread 1000
Running with 20*40 (== 800) tasks.
# dmesg | grep kmemleak
...
kmemleak: 480 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
kmemleak: 665 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
# cat /sys/kernel/debug/kmemleak
unreferenced object 0xffff888cd8ca2c40 (size 64):
comm "hackbench", pid 17142, jiffies 4299780315
hex dump (first 32 bytes):
ac 74 49 00 01 00 00 00 4c 84 49 00 01 00 00 00 .tI.....L.I.....
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace (crc bff18fd4):
[<ffffffff81419a89>] __kmalloc_cache_noprof+0x2f9/0x3f0
[<ffffffff8113f715>] task_numa_work+0x725/0xa00
[<ffffffff8110f878>] task_work_run+0x58/0x90
[<ffffffff81ddd9f8>] syscall_exit_to_user_mode+0x1c8/0x1e0
[<ffffffff81dd78d5>] do_syscall_64+0x85/0x150
[<ffffffff81e0012b>] entry_SYSCALL_64_after_hwframe+0x76/0x7e
...
This issue can be consistently reproduced on three different servers:
* a 448-core server
* a 256-core server
* a 192-core server
[Root Cause]
Since multiple threads are created by the hackbench program (along with
the command argument 'thread'), a shared vma might be accessed by two or
more cores simultaneously. When two or more cores observe that
vma->numab_state is NULL at the same time, vma->numab_state will be
overwritten.
Although current code ensures that only one thread scans the VMAs in a
single 'numa_scan_period', there might be a chance for another thread
to enter in the next 'numa_scan_period' while we have not gotten till
numab_state allocation [1].
Note that the command `/opt/ltp/testcases/bin/hackbench 50 process 1000`
cannot the reproduce the issue. It is verified with 200+ test runs.
[Solution]
Use the cmpxchg atomic operation to ensure that only one thread executes
the vma->numab_state assignment.
[1] https://lore.kernel.org/lkml/1794be3c-358c-4cdc-a43d-a1f841d91ef7@amd.com/
Link: https://lkml.kernel.org/r/20241113102146.2384-1-ahuang12@lenovo.com
Fixes: ef6a22b70f ("sched/numa: apply the scan delay to every new vma")
Signed-off-by: Adrian Huang <ahuang12@lenovo.com>
Reported-by: Jiwei Sun <sunjw10@lenovo.com>
Reviewed-by: Raghavendra K T <raghavendra.kt@amd.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Ben Segall <bsegall@google.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Rely on the NUMA scheduling domain topology, instead of accessing NUMA
topology information directly.
There is basically no functional change, but in this way we ensure
consistent use of the same topology information determined by the
scheduling subsystem.
Fixes: f6ce6b9493 ("sched_ext: Do not enable LLC/NUMA optimizations when domains overlap")
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
As all the non-domain and non-managed_irq housekeeping types have been
unified to HK_TYPE_KERNEL_NOISE, replace all these references in the
scheduler to use HK_TYPE_KERNEL_NOISE.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20241030175253.125248-5-longman@redhat.com
The housekeeping cpumasks are only set by two boot commandline
parameters: "nohz_full" and "isolcpus". When there is more than one of
"nohz_full" or "isolcpus", the extra ones must have the same CPU list
or the setup will fail partially.
The HK_TYPE_DOMAIN and HK_TYPE_MANAGED_IRQ types are settable by
"isolcpus" only and their settings can be independent of the other
types. The other housekeeping types are all set by "nohz_full" or
"isolcpus=nohz" without a way to set them individually. So they all
have identical cpumasks.
There is actually no point in having different cpumasks for these
"nohz_full" only housekeeping types. Consolidate these types to use the
same cpumask by aliasing them to the same value. If there is a need to
set any of them independently in the future, we can break them out to
their own cpumasks again.
With this change, the number of cpumasks in the housekeeping structure
drops from 9 to 3. Other than that, there should be no other functional
change.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20241030175253.125248-4-longman@redhat.com
The "isolcpus=nohz" boot parameter and flag were used to disable tick
when running a single task. Nowsdays, this "nohz" flag is seldomly used
as it is included as part of the "nohz_full" parameter. Extend this
flag to cover other kernel noises disabled by the "nohz_full" parameter
to make them equivalent. This also eliminates the need to use both the
"isolcpus" and the "nohz_full" parameters to fully isolated a given
set of CPUs.
Suggested-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20241030175253.125248-3-longman@redhat.com
The HK_TYPE_SCHED housekeeping type is defined but not set anywhere. So
any code that try to use HK_TYPE_SCHED are essentially dead code. So
remove HK_TYPE_SCHED and any code that use it.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20241030175253.125248-2-longman@redhat.com
Andy reported that clang gets upset with CONFIG_CFS_BANDWIDTH=n:
kernel/sched/fair.c:6580:20: error: unused function 'cfs_bandwidth_used' [-Werror,-Wunused-function]
6580 | static inline bool cfs_bandwidth_used(void)
| ^~~~~~~~~~~~~~~~~~
Indeed, cfs_bandwidth_used() is only used within functions defined under
CONFIG_CFS_BANDWIDTH=y. Remove its CONFIG_CFS_BANDWIDTH=n declaration &
definition.
Reported-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20241127165501.160004-1-vschneid@redhat.com
After commit b58652db66 ("sched/deadline: Fix task_struct reference
leak"), I identified additional calls to hrtimer_try_to_cancel that
might also require a dl_server check. It remains unclear whether this
omission was intentional or accidental in those contexts.
This patch consolidates the timer cancellation logic into dedicated
functions, ensuring consistent behavior across all calls.
Additionally, it reduces code duplication and improves overall code
cleanliness.
Note the use of the __always_inline keyword. In some instances, we
have a task_struct pointer, dereference the dl member, and then use
the container_of macro to retrieve the task_struct pointer again. By
inlining the code, the compiler can potentially optimize out this
redundant round trip.
Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lore.kernel.org/r/20240724142253.27145-3-wander@redhat.com
Currently we check for bandwidth overflow potentially due to hotplug
operations at the end of sched_cpu_deactivate(), after the cpu going
offline has already been removed from scheduling, active_mask, etc.
This can create issues for DEADLINE tasks, as there is a substantial
race window between the start of sched_cpu_deactivate() and the moment
we possibly decide to roll-back the operation if dl_bw_deactivate()
returns failure in cpuset_cpu_inactive(). An example is a throttled
task that sees its replenishment timer firing while the cpu it was
previously running on is considered offline, but before
dl_bw_deactivate() had a chance to say no and roll-back happened.
Fix this by directly calling dl_bw_deactivate() first thing in
sched_cpu_deactivate() and do the required calculation in the former
function considering the cpu passed as an argument as offline already.
By doing so we also simplify sched_cpu_deactivate(), as there is no need
anymore for any kind of roll-back if we fail early.
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Tested-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/Zzc1DfPhbvqDDIJR@jlelli-thinkpadt14gen4.remote.csb
For hotplug operations, DEADLINE needs to check that there is still enough
bandwidth left after removing the CPU that is going offline. We however
fail to do so currently.
Restore the correct behavior by restructuring dl_bw_manage() a bit, so
that overflow conditions (not enough bandwidth left) are properly
checked. Also account for dl_server bandwidth, i.e. discount such
bandwidth in the calculation since NORMAL tasks will be anyway moved
away from the CPU as a result of the hotplug operation.
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Tested-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20241114142810.794657-3-juri.lelli@redhat.com
When root domain non-destructive changes (e.g., only modifying one of
the existing root domains while the rest is not touched) happen we still
need to clear DEADLINE bandwidth accounting so that it's then properly
restored, taking into account DEADLINE tasks associated to each cpuset
(associated to each root domain). After the introduction of dl_servers,
we fail to restore such servers contribution after non-destructive
changes (as they are only considered on destructive changes when
runqueues are attached to the new domains).
Fix this by making sure we iterate over the dl_servers attached to
domains that have not been destroyed and add their bandwidth
contribution back correctly.
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Tested-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20241114142810.794657-2-juri.lelli@redhat.com
