1 // Copyright 2016 Google Inc. All rights reserved
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 // +build ignore
16
17 #include "affinity.h"
18
19 #include "flags.h"
20 #include "log.h"
21
22 #ifdef __linux__
23
24 #include <random>
25
26 #include <sched.h>
27 #include <sys/types.h>
28 #include <unistd.h>
29
SetAffinityForSingleThread()30 void SetAffinityForSingleThread() {
31 cpu_set_t cs;
32 CPU_ZERO(&cs);
33 std::random_device generator;
34 std::uniform_int_distribution<int> distribution(0, g_flags.num_cpus - 1);
35 int cpu = distribution(generator);
36
37 // Try to come up with a CPU and one close to it. This should work on most
38 // hyperthreaded system, but may be less optimal under stranger setups.
39 // Choosing two completely different CPUs would work here as well, it's just a
40 // couple percent faster if they're close (and still faster than letting the
41 // scheduler do whatever it wants).
42 cpu = cpu - (cpu % 2);
43 CPU_SET(cpu, &cs);
44 if (g_flags.num_cpus > 1)
45 CPU_SET(cpu + 1, &cs);
46
47 if (sched_setaffinity(0, sizeof(cs), &cs) < 0)
48 WARN("sched_setaffinity: %s", strerror(errno));
49 }
50
SetAffinityForMultiThread()51 void SetAffinityForMultiThread() {
52 cpu_set_t cs;
53 CPU_ZERO(&cs);
54 for (int i = 0; i < g_flags.num_cpus; i++) {
55 CPU_SET(i, &cs);
56 }
57 if (sched_setaffinity(0, sizeof(cs), &cs) < 0)
58 WARN("sched_setaffinity: %s", strerror(errno));
59 }
60
61 #else
62
SetAffinityForSingleThread()63 void SetAffinityForSingleThread() {}
SetAffinityForMultiThread()64 void SetAffinityForMultiThread() {}
65
66 #endif
67