// SPDX-License-Identifier: GPL-2.0
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/* Manage affinity to optimize IPIs inside the kernel perf API. */
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#define _GNU_SOURCE 1
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#include <sched.h>
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#include <stdlib.h>
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#include <linux/bitmap.h>
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#include <linux/zalloc.h>
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#include "perf.h"
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#include "cpumap.h"
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#include "affinity.h"
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static int get_cpu_set_size(void)
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{
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int sz = cpu__max_cpu() + 8 - 1;
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/*
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* sched_getaffinity doesn't like masks smaller than the kernel.
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* Hopefully that's big enough.
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*/
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if (sz < 4096)
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sz = 4096;
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return sz / 8;
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}
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int affinity__setup(struct affinity *a)
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{
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int cpu_set_size = get_cpu_set_size();
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a->orig_cpus = bitmap_alloc(cpu_set_size * 8);
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if (!a->orig_cpus)
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return -1;
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sched_getaffinity(0, cpu_set_size, (cpu_set_t *)a->orig_cpus);
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a->sched_cpus = bitmap_alloc(cpu_set_size * 8);
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if (!a->sched_cpus) {
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zfree(&a->orig_cpus);
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return -1;
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}
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bitmap_zero((unsigned long *)a->sched_cpus, cpu_set_size);
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a->changed = false;
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return 0;
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}
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/*
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* perf_event_open does an IPI internally to the target CPU.
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* It is more efficient to change perf's affinity to the target
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* CPU and then set up all events on that CPU, so we amortize
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* CPU communication.
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*/
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void affinity__set(struct affinity *a, int cpu)
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{
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int cpu_set_size = get_cpu_set_size();
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if (cpu == -1)
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return;
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a->changed = true;
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set_bit(cpu, a->sched_cpus);
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/*
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* We ignore errors because affinity is just an optimization.
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* This could happen for example with isolated CPUs or cpusets.
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* In this case the IPIs inside the kernel's perf API still work.
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*/
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sched_setaffinity(0, cpu_set_size, (cpu_set_t *)a->sched_cpus);
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clear_bit(cpu, a->sched_cpus);
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}
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void affinity__cleanup(struct affinity *a)
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{
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int cpu_set_size = get_cpu_set_size();
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if (a->changed)
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sched_setaffinity(0, cpu_set_size, (cpu_set_t *)a->orig_cpus);
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zfree(&a->sched_cpus);
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zfree(&a->orig_cpus);
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}
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