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sched: Enable PREEMPT_DYNAMIC for PREEMPT_RT

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In order to enable PREEMPT_DYNAMIC for PREEMPT_RT, remove PREEMPT_RT
from the 'Preemption Model' choice. Strictly speaking PREEMPT_RT is
not a change in how preemption works, but rather it makes a ton more
code preemptible.

Notably, take away NONE and VOLUNTARY options for PREEMPT_RT, they make
no sense (but are techincally possible).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lkml.kernel.org/r/20241007075055.441622332@infradead.org
This commit is contained in:
Peter Zijlstra 2024-10-04 14:46:56 +02:00
parent 7c70cb94d2
commit 35772d627b
3 changed files with 11 additions and 7 deletions
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12
kernel/Kconfig.preempt
View File

@ -20,6 +20,7 @@ choice
config PREEMPT_NONE
bool "No Forced Preemption (Server)"
depends on !PREEMPT_RT
select PREEMPT_NONE_BUILD if !PREEMPT_DYNAMIC
help
This is the traditional Linux preemption model, geared towards
@ -35,6 +36,7 @@ config PREEMPT_NONE
config PREEMPT_VOLUNTARY
bool "Voluntary Kernel Preemption (Desktop)"
depends on !ARCH_NO_PREEMPT
depends on !PREEMPT_RT
select PREEMPT_VOLUNTARY_BUILD if !PREEMPT_DYNAMIC
help
This option reduces the latency of the kernel by adding more
@ -54,7 +56,7 @@ config PREEMPT_VOLUNTARY
config PREEMPT
bool "Preemptible Kernel (Low-Latency Desktop)"
depends on !ARCH_NO_PREEMPT
select PREEMPT_BUILD
select PREEMPT_BUILD if !PREEMPT_DYNAMIC
help
This option reduces the latency of the kernel by making
all kernel code (that is not executing in a critical section)
@ -74,7 +76,7 @@ config PREEMPT_LAZY
bool "Scheduler controlled preemption model"
depends on !ARCH_NO_PREEMPT
depends on ARCH_HAS_PREEMPT_LAZY
select PREEMPT_BUILD
select PREEMPT_BUILD if !PREEMPT_DYNAMIC
help
This option provides a scheduler driven preemption model that
is fundamentally similar to full preemption, but is less
@ -82,6 +84,8 @@ config PREEMPT_LAZY
reduce lock holder preemption and recover some of the performance
gains seen from using Voluntary preemption.
endchoice
config PREEMPT_RT
bool "Fully Preemptible Kernel (Real-Time)"
depends on EXPERT && ARCH_SUPPORTS_RT
@ -99,8 +103,6 @@ config PREEMPT_RT
Select this if you are building a kernel for systems which
require real-time guarantees.
endchoice
config PREEMPT_COUNT
bool
@ -110,7 +112,7 @@ config PREEMPTION
config PREEMPT_DYNAMIC
bool "Preemption behaviour defined on boot"
depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT
depends on HAVE_PREEMPT_DYNAMIC
select JUMP_LABEL if HAVE_PREEMPT_DYNAMIC_KEY
select PREEMPT_BUILD
default y if HAVE_PREEMPT_DYNAMIC_CALL

2
kernel/sched/core.c
View File

@ -7450,11 +7450,13 @@ int preempt_dynamic_mode = preempt_dynamic_undefined;
int sched_dynamic_mode(const char *str)
{
#ifndef CONFIG_PREEMPT_RT
if (!strcmp(str, "none"))
return preempt_dynamic_none;
if (!strcmp(str, "voluntary"))
return preempt_dynamic_voluntary;
#endif
if (!strcmp(str, "full"))
return preempt_dynamic_full;

4
kernel/sched/debug.c
View File

@ -248,9 +248,9 @@ static int sched_dynamic_show(struct seq_file *m, void *v)
"none", "voluntary", "full", "lazy",
};
int j = ARRAY_SIZE(preempt_modes) - !IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY);
int i;
int i = IS_ENABLED(CONFIG_PREEMPT_RT) * 2;
for (i = 0; i < j; i++) {
for (; i < j; i++) {
if (preempt_dynamic_mode == i)
seq_puts(m, "(");
seq_puts(m, preempt_modes[i]);