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// 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);
}
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