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Commit ffa83fb5 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Optimize rcu_needs_cpu() for RCU_NOCB_CPU_ALL 



If CONFIG_RCU_NOCB_CPU_ALL=y, then rcu_needs_cpu() will always
return false, however, the current version nevertheless checks
for RCU callbacks.  This commit therefore creates a static inline
implementation of rcu_needs_cpu() that unconditionally returns false
when CONFIG_RCU_NOCB_CPU_ALL=y.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 2f33b512

include/linux/rcupdate.h

+8 −0
Original line number Diff line number Diff line
@@ -1015,6 +1015,14 @@ static inline notrace void rcu_read_unlock_sched_notrace(void) 
#define kfree_rcu(ptr, rcu_head)					\

	__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))



#if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL)

static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)

{

	*delta_jiffies = ULONG_MAX;

	return 0;

}

#endif /* #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) */



#if defined(CONFIG_RCU_NOCB_CPU_ALL)

static inline bool rcu_is_nocb_cpu(int cpu) { return true; }

#elif defined(CONFIG_RCU_NOCB_CPU)

include/linux/rcutiny.h

+0 −6
Original line number Diff line number Diff line
@@ -68,12 +68,6 @@ static inline void kfree_call_rcu(struct rcu_head *head, 
	call_rcu(head, func);

}



static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)

{

	*delta_jiffies = ULONG_MAX;

	return 0;

}



static inline void rcu_note_context_switch(int cpu)

{

	rcu_sched_qs(cpu);

include/linux/rcutree.h

+2 −0
Original line number Diff line number Diff line
@@ -31,7 +31,9 @@ 
#define __LINUX_RCUTREE_H



void rcu_note_context_switch(int cpu);

#ifndef CONFIG_RCU_NOCB_CPU_ALL

int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies);

#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */

void rcu_cpu_stall_reset(void);



/*

kernel/rcu/tree.c

+1 −1
Original line number Diff line number Diff line
@@ -2880,7 +2880,7 @@ static int rcu_pending(int cpu) 
 * non-NULL, store an indication of whether all callbacks are lazy.

 * (If there are no callbacks, all of them are deemed to be lazy.)

 */

static int rcu_cpu_has_callbacks(int cpu, bool *all_lazy)

static int __maybe_unused rcu_cpu_has_callbacks(int cpu, bool *all_lazy)

{

	bool al = true;

	bool hc = false;

kernel/rcu/tree_plugin.h

+4 −0
Original line number Diff line number Diff line
@@ -1586,11 +1586,13 @@ static void rcu_prepare_kthreads(int cpu) 
 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs

 * any flavor of RCU.

 */

#ifndef CONFIG_RCU_NOCB_CPU_ALL

int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)

{

	*delta_jiffies = ULONG_MAX;

	return rcu_cpu_has_callbacks(cpu, NULL);

}

#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */



/*

 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
@@ -1696,6 +1698,7 @@ static bool rcu_try_advance_all_cbs(void) 
 *

 * The caller must have disabled interrupts.

 */

#ifndef CONFIG_RCU_NOCB_CPU_ALL

int rcu_needs_cpu(int cpu, unsigned long *dj)

{

	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
@@ -1726,6 +1729,7 @@ int rcu_needs_cpu(int cpu, unsigned long *dj) 
	}

	return 0;

}

#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */



/*

 * Prepare a CPU for idle from an RCU perspective.  The first major task