Re: [PATCH v2 2/5] preempt/dynamic: Introduce preempt mode accessors
From: Christophe Leroy <hidden>
Date: 2021-11-16 13:29:58
Also in:
linux-kbuild, lkml
Le 10/11/2021 à 21:24, Valentin Schneider a écrit :
quoted hunk ↗ jump to hunk
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 <redacted> --- 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.
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+ +#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) { }