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preempt/dynamic: Introduce preemption model accessors

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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. Same problem applies to CONFIG_PREEMPTION.

Introduce a set of helpers to determine the actual preemption model used by
the live kernel.

Suggested-by: Marco Elver <elver@google.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Marco Elver <elver@google.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20211112185203.280040-3-valentin.schneider@arm.com
This commit is contained in:
Valentin Schneider 2021-11-12 18:52:01 +00:00 committed by Peter Zijlstra
parent 3123109284
commit cfe43f478b
2 changed files with 53 additions and 0 deletions
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41
include/linux/sched.h
View File

@ -2117,6 +2117,47 @@ static inline void cond_resched_rcu(void)
#endif
}
#ifdef CONFIG_PREEMPT_DYNAMIC
extern bool preempt_model_none(void);
extern bool preempt_model_voluntary(void);
extern bool preempt_model_full(void);
#else
static inline bool preempt_model_none(void)
{
return IS_ENABLED(CONFIG_PREEMPT_NONE);
}
static inline bool preempt_model_voluntary(void)
{
return IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY);
}
static inline bool preempt_model_full(void)
{
return IS_ENABLED(CONFIG_PREEMPT);
}
#endif
static inline bool preempt_model_rt(void)
{
return IS_ENABLED(CONFIG_PREEMPT_RT);
}
/*
* Does the preemption model allow non-cooperative preemption?
*
* For !CONFIG_PREEMPT_DYNAMIC kernels this is an exact match with
* CONFIG_PREEMPTION; for CONFIG_PREEMPT_DYNAMIC this doesn't work as the
* kernel is *built* with CONFIG_PREEMPTION=y but may run with e.g. the
* PREEMPT_NONE model.
*/
static inline bool preempt_model_preemptible(void)
{
return preempt_model_full() || preempt_model_rt();
}
/*
* Does a critical section need to be broken due to another
* task waiting?: (technically does not depend on CONFIG_PREEMPTION,

12
kernel/sched/core.c
View File

@ -8409,6 +8409,18 @@ static void __init preempt_dynamic_init(void)
}
}
#define PREEMPT_MODEL_ACCESSOR(mode) \
bool preempt_model_##mode(void) \
{ \
WARN_ON_ONCE(preempt_dynamic_mode == preempt_dynamic_undefined); \
return preempt_dynamic_mode == preempt_dynamic_##mode; \
} \
EXPORT_SYMBOL_GPL(preempt_model_##mode)
PREEMPT_MODEL_ACCESSOR(none);
PREEMPT_MODEL_ACCESSOR(voluntary);
PREEMPT_MODEL_ACCESSOR(full);
#else /* !CONFIG_PREEMPT_DYNAMIC */
static inline void preempt_dynamic_init(void) { }