Merge pull request #112 from danw/random_affinity
Randomize cpu affinity
diff --git a/affinity.cc b/affinity.cc
index 2101fdb..5448b29 100644
--- a/affinity.cc
+++ b/affinity.cc
@@ -21,15 +21,29 @@
#ifdef __linux__
+#include <random>
+
#include <sched.h>
+#include <sys/types.h>
+#include <unistd.h>
void SetAffinityForSingleThread() {
cpu_set_t cs;
CPU_ZERO(&cs);
- int n = g_flags.num_cpus / 2;
- CPU_SET(n, &cs);
- if (n > 1)
- CPU_SET(n + 1, &cs);
+ std::default_random_engine generator(getpid());
+ std::uniform_int_distribution<int> distribution(0,g_flags.num_cpus-1);
+ int cpu = distribution(generator);
+
+ // Try to come up with a CPU and one close to it. This should work on most
+ // hyperthreaded system, but may be less optimal under stranger setups.
+ // Choosing two completely different CPUs would work here as well, it's just a
+ // couple percent faster if they're close (and still faster than letting the
+ // scheduler do whatever it wants).
+ cpu = cpu - (cpu % 2);
+ CPU_SET(cpu, &cs);
+ if (g_flags.num_cpus > 1)
+ CPU_SET(cpu+1, &cs);
+
if (sched_setaffinity(0, sizeof(cs), &cs) < 0)
WARN("sched_setaffinity: %s", strerror(errno));
}
