Commit 14e292f8 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched,rt: Use cpumask_any*_distribute() 



Replace a bunch of cpumask_any*() instances with
cpumask_any*_distribute(), by injecting this little bit of random in
cpu selection, we reduce the chance two competing balance operations
working off the same lowest_mask pick the same CPU.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Reviewed-by: default avatarDaniel Bristot de Oliveira <bristot@redhat.com>
Link: https://lkml.kernel.org/r/20201023102347.190759694@infradead.org
parent 3015ef4b

include/linux/cpumask.h

+6 −0
Original line number Diff line number Diff line
@@ -199,6 +199,11 @@ static inline int cpumask_any_and_distribute(const struct cpumask *src1p, 
	return cpumask_next_and(-1, src1p, src2p);

}



static inline int cpumask_any_distribute(const struct cpumask *srcp)

{

	return cpumask_first(srcp);

}



#define for_each_cpu(cpu, mask)			\

	for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask)

#define for_each_cpu_not(cpu, mask)		\
@@ -252,6 +257,7 @@ int cpumask_any_but(const struct cpumask *mask, unsigned int cpu); 
unsigned int cpumask_local_spread(unsigned int i, int node);

int cpumask_any_and_distribute(const struct cpumask *src1p,

			       const struct cpumask *src2p);

int cpumask_any_distribute(const struct cpumask *srcp);



/**

 * for_each_cpu - iterate over every cpu in a mask

kernel/sched/deadline.c

+3 −3
Original line number Diff line number Diff line
@@ -2002,7 +2002,7 @@ static int find_later_rq(struct task_struct *task) 
				return this_cpu;

			}



			best_cpu = cpumask_first_and(later_mask,

			best_cpu = cpumask_any_and_distribute(later_mask,

							      sched_domain_span(sd));

			/*

			 * Last chance: if a CPU being in both later_mask
@@ -2025,7 +2025,7 @@ static int find_later_rq(struct task_struct *task) 
	if (this_cpu != -1)

		return this_cpu;



	cpu = cpumask_any(later_mask);

	cpu = cpumask_any_distribute(later_mask);

	if (cpu < nr_cpu_ids)

		return cpu;

kernel/sched/rt.c

+3 −3
Original line number Diff line number Diff line
@@ -1752,7 +1752,7 @@ static int find_lowest_rq(struct task_struct *task) 
				return this_cpu;

			}



			best_cpu = cpumask_first_and(lowest_mask,

			best_cpu = cpumask_any_and_distribute(lowest_mask,

							      sched_domain_span(sd));

			if (best_cpu < nr_cpu_ids) {

				rcu_read_unlock();
@@ -1770,7 +1770,7 @@ static int find_lowest_rq(struct task_struct *task) 
	if (this_cpu != -1)

		return this_cpu;



	cpu = cpumask_any(lowest_mask);

	cpu = cpumask_any_distribute(lowest_mask);

	if (cpu < nr_cpu_ids)

		return cpu;

lib/cpumask.c

+18 −0
Original line number Diff line number Diff line
@@ -267,3 +267,21 @@ int cpumask_any_and_distribute(const struct cpumask *src1p, 
	return next;

}

EXPORT_SYMBOL(cpumask_any_and_distribute);



int cpumask_any_distribute(const struct cpumask *srcp)

{

	int next, prev;



	/* NOTE: our first selection will skip 0. */

	prev = __this_cpu_read(distribute_cpu_mask_prev);



	next = cpumask_next(prev, srcp);

	if (next >= nr_cpu_ids)

		next = cpumask_first(srcp);



	if (next < nr_cpu_ids)

		__this_cpu_write(distribute_cpu_mask_prev, next);



	return next;

}

EXPORT_SYMBOL(cpumask_any_distribute);

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