On Tue, Nov 07, 2023 at 01:57:29PM -0800, Ankur Arora wrote: > The scheduler uses PREEMPT_COUNT and PREEMPTION to drive > preemption: the first to demarcate non-preemptible sections and > the second for the actual mechanics of preemption. > > Enable both for voluntary preemption models. > > In addition, define a new scheduler feature FORCE_PREEMPT which > can now be used to distinguish between voluntary and full > preemption models at runtime. > > Originally-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx> > --- > init/Makefile | 2 +- > kernel/Kconfig.preempt | 12 ++++++++---- > kernel/entry/common.c | 3 +-- > kernel/sched/core.c | 26 +++++++++++--------------- > kernel/sched/features.h | 6 ++++++ > 5 files changed, 27 insertions(+), 22 deletions(-) > > diff --git a/init/Makefile b/init/Makefile > index 385fd80fa2ef..99e480f24cf3 100644 > --- a/init/Makefile > +++ b/init/Makefile > @@ -24,7 +24,7 @@ mounts-$(CONFIG_BLK_DEV_INITRD) += do_mounts_initrd.o > # > > smp-flag-$(CONFIG_SMP) := SMP > -preempt-flag-$(CONFIG_PREEMPT) := PREEMPT > +preempt-flag-$(CONFIG_PREEMPTION) := PREEMPT_DYNAMIC > preempt-flag-$(CONFIG_PREEMPT_RT) := PREEMPT_RT > > build-version = $(or $(KBUILD_BUILD_VERSION), $(build-version-auto)) > diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt > index aa87b5cd3ecc..074fe5e253b5 100644 > --- a/kernel/Kconfig.preempt > +++ b/kernel/Kconfig.preempt > @@ -6,20 +6,23 @@ choice > > config PREEMPT_NONE > bool "No Forced Preemption (Server)" > + select PREEMPTION > help > This is the traditional Linux preemption model, geared towards > throughput. It will still provide good latencies most of the > - time, but there are no guarantees and occasional longer delays > - are possible. > + time, but occasional delays are possible. > > Select this option if you are building a kernel for a server or > scientific/computation system, or if you want to maximize the > raw processing power of the kernel, irrespective of scheduling > - latencies. > + latencies. Unless your architecture actively disables preemption, > + you can always switch to one of the other preemption models > + at runtime. > diff --git a/kernel/entry/common.c b/kernel/entry/common.c > index 6433e6c77185..f7f2efabb5b5 100644 > --- a/kernel/entry/common.c > +++ b/kernel/entry/common.c > @@ -422,8 +422,7 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state) > } > > instrumentation_begin(); > - if (IS_ENABLED(CONFIG_PREEMPTION)) > - irqentry_exit_cond_resched(); > + irqentry_exit_cond_resched(); > /* Covers both tracing and lockdep */ > trace_hardirqs_on(); > instrumentation_end(); I'm totally confused by the PREEMPT_NONE changes here. How does that make sense?
