Commit 267ed5d8 authored by Andi Kleen's avatar Andi Kleen Committed by Arnaldo Carvalho de Melo
Browse files

perf affinity: Add infrastructure to save/restore affinity 



The kernel perf subsystem has to IPI to the target CPU for many
operations. On systems with many CPUs and when managing many events the
overhead can be dominated by lots of IPIs.

An alternative is to set up CPU affinity in the perf tool, then set up
all the events for that CPU, and then move on to the next CPU.

Add some affinity management infrastructure to enable such a model.
Used in followon patches.

Committer notes:

Use zfree() in some places, add missing stdbool.h header, some minor
coding style changes.

Signed-off-by: default avatarAndi Kleen <ak@linux.intel.com>
Acked-by: default avatarJiri Olsa <jolsa@kernel.org>
Link: http://lore.kernel.org/lkml/20191121001522.180827-3-andi@firstfloor.org


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent d9664582

tools/perf/util/Build

+1 −0
Original line number Diff line number Diff line
@@ -77,6 +77,7 @@ perf-y += sort.o 
perf-y += hist.o

perf-y += util.o

perf-y += cpumap.o

perf-y += affinity.o

perf-y += cputopo.o

perf-y += cgroup.o

perf-y += target.o

tools/perf/util/affinity.c

0 → 100644
+73 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

/* Manage affinity to optimize IPIs inside the kernel perf API. */

#define _GNU_SOURCE 1

#include <sched.h>

#include <stdlib.h>

#include <linux/bitmap.h>

#include <linux/zalloc.h>

#include "perf.h"

#include "cpumap.h"

#include "affinity.h"



static int get_cpu_set_size(void)

{

	int sz = cpu__max_cpu() + 8 - 1;

	/*

	 * sched_getaffinity doesn't like masks smaller than the kernel.

	 * Hopefully that's big enough.

	 */

	if (sz < 4096)

		sz = 4096;

	return sz / 8;

}



int affinity__setup(struct affinity *a)

{

	int cpu_set_size = get_cpu_set_size();



	a->orig_cpus = bitmap_alloc(cpu_set_size * 8);

	if (!a->orig_cpus)

		return -1;

	sched_getaffinity(0, cpu_set_size, (cpu_set_t *)a->orig_cpus);

	a->sched_cpus = bitmap_alloc(cpu_set_size * 8);

	if (!a->sched_cpus) {

		zfree(&a->orig_cpus);

		return -1;

	}

	bitmap_zero((unsigned long *)a->sched_cpus, cpu_set_size);

	a->changed = false;

	return 0;

}



/*

 * perf_event_open does an IPI internally to the target CPU.

 * It is more efficient to change perf's affinity to the target

 * CPU and then set up all events on that CPU, so we amortize

 * CPU communication.

 */

void affinity__set(struct affinity *a, int cpu)

{

	int cpu_set_size = get_cpu_set_size();



	if (cpu == -1)

		return;

	a->changed = true;

	set_bit(cpu, a->sched_cpus);

	/*

	 * We ignore errors because affinity is just an optimization.

	 * This could happen for example with isolated CPUs or cpusets.

	 * In this case the IPIs inside the kernel's perf API still work.

	 */

	sched_setaffinity(0, cpu_set_size, (cpu_set_t *)a->sched_cpus);

	clear_bit(cpu, a->sched_cpus);

}



void affinity__cleanup(struct affinity *a)

{

	int cpu_set_size = get_cpu_set_size();



	if (a->changed)

		sched_setaffinity(0, cpu_set_size, (cpu_set_t *)a->orig_cpus);

	zfree(&a->sched_cpus);

	zfree(&a->orig_cpus);

}

tools/perf/util/affinity.h

0 → 100644
+17 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#ifndef PERF_AFFINITY_H

#define PERF_AFFINITY_H 1



#include <stdbool.h>



struct affinity {

	unsigned long *orig_cpus;

	unsigned long *sched_cpus;

	bool changed;

};



void affinity__cleanup(struct affinity *a);

void affinity__set(struct affinity *a, int cpu);

int affinity__setup(struct affinity *a);



#endif // PERF_AFFINITY_H

tools/perf/util/python-ext-sources

+1 −0
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@@ -33,3 +33,4 @@ util/trace-event.c 
util/string.c

util/symbol_fprintf.c

util/units.c

util/affinity.c

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