Messages in this thread | | | Date | Tue, 16 Nov 2021 14:29:51 +0100 | Subject | Re: [PATCH v2 2/5] preempt/dynamic: Introduce preempt mode accessors | From | Christophe Leroy <> |
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Le 10/11/2021 à 21:24, Valentin Schneider a écrit : > CONFIG_PREEMPT{_NONE, _VOLUNTARY} designate either: > o The build-time preemption model when !PREEMPT_DYNAMIC > o The default boot-time preemption model when PREEMPT_DYNAMIC > > IOW, using those on PREEMPT_DYNAMIC kernels is meaningless - the actual > model could have been set to something else by the "preempt=foo" cmdline > parameter. > > Introduce a set of helpers to determine the actual preemption mode used by > the live kernel. > > Suggested-by: Marco Elver <elver@google.com> > Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> > --- > include/linux/sched.h | 16 ++++++++++++++++ > kernel/sched/core.c | 11 +++++++++++ > 2 files changed, 27 insertions(+) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 5f8db54226af..0640d5622496 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -2073,6 +2073,22 @@ static inline void cond_resched_rcu(void) > #endif > } > > +#ifdef CONFIG_PREEMPT_DYNAMIC > + > +extern bool is_preempt_none(void); > +extern bool is_preempt_voluntary(void); > +extern bool is_preempt_full(void);
Those are trivial tests supposed to be used in fast pathes. They should be static inlines in order to minimise the overhead.
> + > +#else > + > +#define is_preempt_none() IS_ENABLED(CONFIG_PREEMPT_NONE) > +#define is_preempt_voluntary() IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY) > +#define is_preempt_full() IS_ENABLED(CONFIG_PREEMPT)
Would be better to use static inlines here as well instead of macros.
> + > +#endif > + > +#define is_preempt_rt() IS_ENABLED(CONFIG_PREEMPT_RT) > + > /* > * Does a critical section need to be broken due to another > * task waiting?: (technically does not depend on CONFIG_PREEMPTION, > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 97047aa7b6c2..9db7f77e53c3 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6638,6 +6638,17 @@ static void __init preempt_dynamic_init(void) > } > } > > +#define PREEMPT_MODE_ACCESSOR(mode) \ > + bool is_preempt_##mode(void) \ > + { \ > + WARN_ON_ONCE(preempt_dynamic_mode == preempt_dynamic_undefined); \
Not sure using WARN_ON is a good idea here, as it may be called very early, see comment on powerpc patch.
> + return preempt_dynamic_mode == preempt_dynamic_##mode; \ > + }
I'm not sure that's worth a macro. You only have 3 accessors, 2 lines of code each. Just define all 3 in plain text.
CONFIG_PREEMPT_DYNAMIC is based on using strategies like static_calls in order to minimise the overhead. For those accessors you should use the same kind of approach and use things like jump_labels in order to not redo the test at each time and minimise overhead as much as possible.
> + > +PREEMPT_MODE_ACCESSOR(none) > +PREEMPT_MODE_ACCESSOR(voluntary) > +PREEMPT_MODE_ACCESSOR(full) > + > #else /* !CONFIG_PREEMPT_DYNAMIC */ > > static inline void preempt_dynamic_init(void) { } >
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