Messages in this thread Patch in this message | | | From | Marco Elver <> | Date | Wed, 10 Nov 2021 16:03:10 +0100 | Subject | Re: [PATCH] sched: Split preemption model selection between DYNAMIC & !DYNAMIC |
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On Wed, 10 Nov 2021 at 15:45, Valentin Schneider <valentin.schneider@arm.com> wrote: > > On 10/11/21 11:24, Valentin Schneider wrote: > > Following Frederic's _STATIC suggestion, I got to the below. The nice thing > > is if a defconfig picks say PREEMPT_VOLUNTARY and the arch supports > > PREEMPT_DYNAMIC, then it'll pick PREEMPT_VOLUNTARY_BEHAVIOUR. The less nice > > thing is that we end up selecting PREEMPT_STATIC for PREEMPT_DYNAMIC > > kernels, naming's hard... Maybe _BUILD rather than _STATIC? > > > > And now without a legacy compatibility layer crud...
If this works for everyone else, then I think this is the least intrusive and hopefully won't require telling everyone about this config change.
For the final version, it seems to be missing s/_BEHAVIOUR// in kernel/sched/core.c.
And the kcsan_test.c change can be reverted, I think it's broken either way now, because it wants the dynamic state (the test still works in most configs, so fixing this isn't super urgent). Similarly for kernel/trace/trace.c, which appears mainly cosmetic. So I'd defer changing these until there are real helpers to get the true preemption behaviour of the running system.
Thanks, -- Marco
> --- > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index 2776423a587e..9c7d774ef809 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -88,7 +88,7 @@ > struct completion; > struct user; > > -#ifdef CONFIG_PREEMPT_VOLUNTARY > +#ifdef CONFIG_PREEMPT_VOLUNTARY_BUILD > > extern int __cond_resched(void); > # define might_resched() __cond_resched() > diff --git a/include/linux/vermagic.h b/include/linux/vermagic.h > index 1eaaa93c37bf..f2b71920024c 100644 > --- a/include/linux/vermagic.h > +++ b/include/linux/vermagic.h > @@ -15,7 +15,7 @@ > #else > #define MODULE_VERMAGIC_SMP "" > #endif > -#ifdef CONFIG_PREEMPT > +#ifdef CONFIG_PREEMPT_BUILD > #define MODULE_VERMAGIC_PREEMPT "preempt " > #elif defined(CONFIG_PREEMPT_RT) > #define MODULE_VERMAGIC_PREEMPT "preempt_rt " > @@ -39,9 +39,9 @@ > #define MODULE_RANDSTRUCT_PLUGIN > #endif > > -#define VERMAGIC_STRING \ > +#define VERMAGIC_STRING \ > UTS_RELEASE " " \ > - MODULE_VERMAGIC_SMP MODULE_VERMAGIC_PREEMPT \ > + MODULE_VERMAGIC_SMP MODULE_VERMAGIC_PREEMPT \ > MODULE_VERMAGIC_MODULE_UNLOAD MODULE_VERMAGIC_MODVERSIONS \ > MODULE_ARCH_VERMAGIC \ > MODULE_RANDSTRUCT_PLUGIN > diff --git a/init/Makefile b/init/Makefile > index 2846113677ee..04eeee12c076 100644 > --- a/init/Makefile > +++ b/init/Makefile > @@ -30,7 +30,7 @@ $(obj)/version.o: include/generated/compile.h > quiet_cmd_compile.h = CHK $@ > cmd_compile.h = \ > $(CONFIG_SHELL) $(srctree)/scripts/mkcompile_h $@ \ > - "$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT)" \ > + "$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT_BUILD)" \ > "$(CONFIG_PREEMPT_RT)" $(CONFIG_CC_VERSION_TEXT) "$(LD)" > > include/generated/compile.h: FORCE > diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt > index 60f1bfc3c7b2..ce77f0265660 100644 > --- a/kernel/Kconfig.preempt > +++ b/kernel/Kconfig.preempt > @@ -1,12 +1,23 @@ > # SPDX-License-Identifier: GPL-2.0-only > > +config PREEMPT_NONE_BUILD > + bool > + > +config PREEMPT_VOLUNTARY_BUILD > + bool > + > +config PREEMPT_BUILD > + bool > + select PREEMPTION > + select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK > + > choice > prompt "Preemption Model" > - default PREEMPT_NONE_BEHAVIOUR > + default PREEMPT_NONE > > -config PREEMPT_NONE_BEHAVIOUR > +config PREEMPT_NONE > bool "No Forced Preemption (Server)" > - select PREEMPT_NONE if !PREEMPT_DYNAMIC > + select PREEMPT_NONE_BUILD if !PREEMPT_DYNAMIC > help > This is the traditional Linux preemption model, geared towards > throughput. It will still provide good latencies most of the > @@ -18,10 +29,10 @@ config PREEMPT_NONE_BEHAVIOUR > raw processing power of the kernel, irrespective of scheduling > latencies. > > -config PREEMPT_VOLUNTARY_BEHAVIOUR > +config PREEMPT_VOLUNTARY > bool "Voluntary Kernel Preemption (Desktop)" > depends on !ARCH_NO_PREEMPT > - select PREEMPT_VOLUNTARY if !PREEMPT_DYNAMIC > + select PREEMPT_VOLUNTARY_BUILD if !PREEMPT_DYNAMIC > help > This option reduces the latency of the kernel by adding more > "explicit preemption points" to the kernel code. These new > @@ -37,10 +48,10 @@ config PREEMPT_VOLUNTARY_BEHAVIOUR > > Select this if you are building a kernel for a desktop system. > > -config PREEMPT_BEHAVIOUR > +config PREEMPT > bool "Preemptible Kernel (Low-Latency Desktop)" > depends on !ARCH_NO_PREEMPT > - select PREEMPT > + select PREEMPT_BUILD > help > This option reduces the latency of the kernel by making > all kernel code (that is not executing in a critical section) > @@ -58,7 +69,7 @@ config PREEMPT_BEHAVIOUR > > config PREEMPT_RT > bool "Fully Preemptible Kernel (Real-Time)" > - depends on EXPERT && ARCH_SUPPORTS_RT && !PREEMPT_DYNAMIC > + depends on EXPERT && ARCH_SUPPORTS_RT > select PREEMPTION > help > This option turns the kernel into a real-time kernel by replacing > @@ -75,17 +86,6 @@ config PREEMPT_RT > > endchoice > > -config PREEMPT_NONE > - bool > - > -config PREEMPT_VOLUNTARY > - bool > - > -config PREEMPT > - bool > - select PREEMPTION > - select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK > - > config PREEMPT_COUNT > bool > > @@ -95,8 +95,8 @@ config PREEMPTION > > config PREEMPT_DYNAMIC > bool "Preemption behaviour defined on boot" > - depends on HAVE_PREEMPT_DYNAMIC > - select PREEMPT > + depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT > + select PREEMPT_BUILD > default y > help > This option allows to define the preemption model on the kernel > diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c > index dc55fd5a36fc..845b17cf7811 100644 > --- a/kernel/kcsan/kcsan_test.c > +++ b/kernel/kcsan/kcsan_test.c > @@ -1005,13 +1005,13 @@ static const void *nthreads_gen_params(const void *prev, char *desc) > else > nthreads *= 2; > > - if (!IS_ENABLED(CONFIG_PREEMPT) || !IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER)) { > + if (!IS_ENABLED(CONFIG_PREEMPTION) || !IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER)) { > /* > * Without any preemption, keep 2 CPUs free for other tasks, one > * of which is the main test case function checking for > * completion or failure. > */ > - const long min_unused_cpus = IS_ENABLED(CONFIG_PREEMPT_NONE) ? 2 : 0; > + const long min_unused_cpus = IS_ENABLED(CONFIG_PREEMPT_NONE_BUILD) ? 2 : 0; > const long min_required_cpus = 2 + min_unused_cpus; > > if (num_online_cpus() < min_required_cpus) { > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 7896d30d90f7..3b3226ffbafa 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -4271,11 +4271,11 @@ print_trace_header(struct seq_file *m, struct trace_iterator *iter) > entries, > total, > buf->cpu, > -#if defined(CONFIG_PREEMPT_NONE) > +#if defined(CONFIG_PREEMPT_NONE_BUILD) > "server", > -#elif defined(CONFIG_PREEMPT_VOLUNTARY) > +#elif defined(CONFIG_PREEMPT_VOLUNTARY_BUILD) > "desktop", > -#elif defined(CONFIG_PREEMPT) > +#elif defined(CONFIG_PREEMPT_BUILD) > "preempt", > #elif defined(CONFIG_PREEMPT_RT) > "preempt_rt",
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