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Fix getting the CPU frequency on OS X

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This commit is contained in:
Eric Fiselier 2016-10-08 01:36:54 -06:00
parent f67ee4ad9b
commit 721c9224b9
1 changed files with 16 additions and 21 deletions
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37
src/sysinfo.cc
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@ -280,29 +280,24 @@ void InitializeSystemInfo() {
// group // group
#elif defined BENCHMARK_OS_MACOSX #elif defined BENCHMARK_OS_MACOSX
// returning "mach time units" per second. the current number of elapsed int32_t num_cpus = 0;
// mach time units can be found by calling uint64 mach_absolute_time();
// while not as precise as actual CPU cycles, it is accurate in the face
// of CPU frequency scaling and multi-cpu/core machines.
// Our mac users have these types of machines, and accuracy
// (i.e. correctness) trumps precision.
// See cycleclock.h: CycleClock::Now(), which returns number of mach time
// units on Mac OS X.
mach_timebase_info_data_t timebase_info;
mach_timebase_info(&timebase_info);
double mach_time_units_per_nanosecond =
static_cast<double>(timebase_info.denom) /
static_cast<double>(timebase_info.numer);
cpuinfo_cycles_per_second = mach_time_units_per_nanosecond * 1e9;
int num_cpus = 0;
size_t size = sizeof(num_cpus); size_t size = sizeof(num_cpus);
int numcpus_name[] = {CTL_HW, HW_NCPU}; if (::sysctlbyname("hw.ncpu", &num_cpus, &size, nullptr, 0) == 0 &&
if (::sysctl(numcpus_name, arraysize(numcpus_name), &num_cpus, &size, nullptr, (size == sizeof(num_cpus))) {
0) == 0 &&
(size == sizeof(num_cpus)))
cpuinfo_num_cpus = num_cpus; cpuinfo_num_cpus = num_cpus;
} else {
fprintf(stderr, "%s\n", strerror(errno));
std::exit(EXIT_FAILURE);
}
int64_t cpu_freq = 0;
size = sizeof(cpu_freq);
if (::sysctlbyname("hw.cpufrequency", &cpu_freq, &size, nullptr, 0) == 0 &&
(size == sizeof(cpu_freq))) {
cpuinfo_cycles_per_second = cpu_freq;
} else {
fprintf(stderr, "%s\n", strerror(errno));
std::exit(EXIT_FAILURE);
}
#else #else
// Generic cycles per second counter // Generic cycles per second counter
cpuinfo_cycles_per_second = static_cast<double>(EstimateCyclesPerSecond()); cpuinfo_cycles_per_second = static_cast<double>(EstimateCyclesPerSecond());