Commit cfe43f47 authored by Valentin Schneider's avatar Valentin Schneider Committed by Peter Zijlstra
Browse files

preempt/dynamic: Introduce preemption model accessors 



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: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarMarco Elver <elver@google.com>
Acked-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20211112185203.280040-3-valentin.schneider@arm.com
parent 31231092

include/linux/sched.h

+41 −0
Original line number Diff line number Diff line
@@ -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,

kernel/sched/core.c

+12 −0
Original line number Diff line number Diff line
@@ -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) { }