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linux: fallback in CalculateCPUSpeed() for cases where perf counters are not available.

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This commit is contained in:
Mari the Deer 2025-09-24 17:32:08 +02:00
commit eb3a17c50f
1 changed files with 46 additions and 7 deletions
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53
src/common/platform/posix/sdl/i_system.cpp
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@ -51,6 +51,7 @@
#include <asm/unistd.h>
#include <linux/perf_event.h>
#include <sys/mman.h>
#include "stats.h"
#endif
#if defined(__sun) || defined(__sun__)
@ -173,7 +174,11 @@ void CalculateCPUSpeed()
PerfToMillisec = PerfToSec*1000.;
#elif defined(__linux__)
// [MK] read from perf values if we can
double mhz;
struct perf_event_attr pe;
struct perf_event_mmap_page *pc;
int fd;
void *addr;
memset(&pe,0,sizeof(struct perf_event_attr));
pe.type = PERF_TYPE_HARDWARE;
pe.size = sizeof(struct perf_event_attr);
@ -181,29 +186,63 @@ void CalculateCPUSpeed()
pe.disabled = 1;
pe.exclude_kernel = 1;
pe.exclude_hv = 1;
int fd = syscall(__NR_perf_event_open, &pe, 0, -1, -1, 0);
fd = syscall(__NR_perf_event_open, &pe, 0, -1, -1, 0);
if (fd == -1)
{
return;
goto calcspeed_fallback;
}
void *addr = mmap(nullptr, 4096, PROT_READ, MAP_SHARED, fd, 0);
addr = mmap(nullptr, 4096, PROT_READ, MAP_SHARED, fd, 0);
if (addr == nullptr)
{
close(fd);
return;
goto calcspeed_fallback;
}
struct perf_event_mmap_page *pc = (struct perf_event_mmap_page *)addr;
pc = (struct perf_event_mmap_page *)addr;
if (pc->cap_user_time != 1)
{
close(fd);
return;
goto calcspeed_fallback;
}
double mhz = (1000LU << pc->time_shift) / (double)pc->time_mult;
mhz = (1000LU << pc->time_shift) / (double)pc->time_mult;
PerfAvailable = true;
PerfToSec = .000001/mhz;
PerfToMillisec = PerfToSec*1000.;
if (!batchrun && !RunningAsTool) Printf("CPU speed: %.0f MHz\n", mhz);
close(fd);
return;
calcspeed_fallback:
// [MK] in cases where the performance counters are not available, use
// a (potentially) less accurate fallback for estimating TSC frequency
//
// (note that by this point, the kernel has definitely flagged the TSC
// as unstable, but this should hopefully not cause any major issues in
// the engine)
struct timespec tenth_second, ts_start, ts_end;
uint64_t tsc_hz, ns, end, start;
double secs;
memset(&tenth_second,0,sizeof(struct timespec));
tenth_second.tv_nsec = 100000000LU;
if (clock_gettime(CLOCK_MONOTONIC_RAW, &ts_start) == 0)
{
start = rdtsc();
nanosleep(&tenth_second,NULL);
clock_gettime(CLOCK_MONOTONIC_RAW, &ts_end);
end = rdtsc();
if ((start == 0) && (end == 0))
{
// rdtsc instruction or equivalent is not available,
// bail out early
return;
}
ns = ((ts_end.tv_sec-ts_start.tv_sec)*1000000000LU);
ns += (ts_end.tv_nsec-ts_start.tv_nsec);
secs = (double)ns/1000000000.;
tsc_hz = (uint64_t)((end-start)/secs);
PerfAvailable = true;
PerfToSec = 1./tsc_hz;
PerfToMillisec = PerfToSec*1000.;
if (!batchrun) Printf("CPU speed: ~%.0f MHz\n", tsc_hz/1000000.);
}
#endif
}