1  // SPDX-License-Identifier: GPL-2.0
2  /* Manage affinity to optimize IPIs inside the kernel perf API. */
3  #define _GNU_SOURCE 1
4  #include <sched.h>
5  #include <stdlib.h>
6  #include <linux/bitmap.h>
7  #include <linux/zalloc.h>
8  #include "perf.h"
9  #include "cpumap.h"
10  #include "affinity.h"
11  
get_cpu_set_size(void)12  static int get_cpu_set_size(void)
13  {
14  	int sz = cpu__max_cpu().cpu + 8 - 1;
15  	/*
16  	 * sched_getaffinity doesn't like masks smaller than the kernel.
17  	 * Hopefully that's big enough.
18  	 */
19  	if (sz < 4096)
20  		sz = 4096;
21  	return sz / 8;
22  }
23  
affinity__setup(struct affinity * a)24  int affinity__setup(struct affinity *a)
25  {
26  	int cpu_set_size = get_cpu_set_size();
27  
28  	a->orig_cpus = bitmap_zalloc(cpu_set_size * 8);
29  	if (!a->orig_cpus)
30  		return -1;
31  	sched_getaffinity(0, cpu_set_size, (cpu_set_t *)a->orig_cpus);
32  	a->sched_cpus = bitmap_zalloc(cpu_set_size * 8);
33  	if (!a->sched_cpus) {
34  		zfree(&a->orig_cpus);
35  		return -1;
36  	}
37  	bitmap_zero((unsigned long *)a->sched_cpus, cpu_set_size);
38  	a->changed = false;
39  	return 0;
40  }
41  
42  /*
43   * perf_event_open does an IPI internally to the target CPU.
44   * It is more efficient to change perf's affinity to the target
45   * CPU and then set up all events on that CPU, so we amortize
46   * CPU communication.
47   */
affinity__set(struct affinity * a,int cpu)48  void affinity__set(struct affinity *a, int cpu)
49  {
50  	int cpu_set_size = get_cpu_set_size();
51  
52  	/*
53  	 * Return:
54  	 * - if cpu is -1
55  	 * - restrict out of bound access to sched_cpus
56  	 */
57  	if (cpu == -1 || ((cpu >= (cpu_set_size * 8))))
58  		return;
59  
60  	a->changed = true;
61  	__set_bit(cpu, a->sched_cpus);
62  	/*
63  	 * We ignore errors because affinity is just an optimization.
64  	 * This could happen for example with isolated CPUs or cpusets.
65  	 * In this case the IPIs inside the kernel's perf API still work.
66  	 */
67  	sched_setaffinity(0, cpu_set_size, (cpu_set_t *)a->sched_cpus);
68  	__clear_bit(cpu, a->sched_cpus);
69  }
70  
__affinity__cleanup(struct affinity * a)71  static void __affinity__cleanup(struct affinity *a)
72  {
73  	int cpu_set_size = get_cpu_set_size();
74  
75  	if (a->changed)
76  		sched_setaffinity(0, cpu_set_size, (cpu_set_t *)a->orig_cpus);
77  	zfree(&a->sched_cpus);
78  	zfree(&a->orig_cpus);
79  }
80  
affinity__cleanup(struct affinity * a)81  void affinity__cleanup(struct affinity *a)
82  {
83  	if (a != NULL)
84  		__affinity__cleanup(a);
85  }
86