Commit 35772d62 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched: Enable PREEMPT_DYNAMIC for PREEMPT_RT 



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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lkml.kernel.org/r/20241007075055.441622332@infradead.org
parent 7c70cb94

kernel/Kconfig.preempt

+7 −5
Original line number Diff line number Diff line
@@ -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

kernel/sched/core.c

+2 −0
Original line number Diff line number Diff line
@@ -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;

kernel/sched/debug.c

+2 −2
Original line number Diff line number Diff line
@@ -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]);