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Add support for s390x cpu frequency #728

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Add support for s390x cpu frequency #728

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12 changes: 12 additions & 0 deletions absl/base/internal/unscaledcycleclock.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -101,6 +101,18 @@ double UnscaledCycleClock::Frequency() {
#endif
}

#elif defined(__s390x__)

int64_t UnscaledCycleClock::Now() {
int64_t tsc;
asm("stck %0" : "=Q" (tsc) : : "cc");
return tsc;
}

double UnscaledCycleClock::Frequency() {
return base_internal::NominalCPUFrequency();
}

#elif defined(__aarch64__)

// System timer of ARMv8 runs at a different frequency than the CPU's.
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4 changes: 2 additions & 2 deletions absl/base/internal/unscaledcycleclock.h
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Expand Up @@ -47,7 +47,7 @@
// The following platforms have an implementation of a hardware counter.
#if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__) || \
defined(__powerpc__) || defined(__ppc__) || \
defined(_M_IX86) || defined(_M_X64)
defined(_M_IX86) || defined(_M_X64) || defined(__s390x__)
#define ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION 1
#else
#define ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION 0
Expand Down Expand Up @@ -81,7 +81,7 @@
// This macro can be used to test if UnscaledCycleClock::Frequency()
// is NominalCPUFrequency() on a particular platform.
#if (defined(__i386__) || defined(__x86_64__) || \
defined(_M_IX86) || defined(_M_X64))
defined(_M_IX86) || defined(_M_X64)) || defined(__s390x__)
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https://groups.google.com/forum/#!topic/bit.listserv.ibm-main/mYYcbXg0lGY makes me think that the counter retreived by the stck instruction is a clock, but not one that runs at the CPU frequency, since it seems constant across chips. Can you point me to documentation that shows otherwise?

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Thanks for the notes. Honestly speaking, I'm not very familiar with instruction set or cpu counter, so I guess what you are suggesting is that stck does not return the correct cpu time so the frequency calculated based on this will not be accurate, am I understanding it correctly? If this is the case, could you please give me a hint of what counter do we need to retrieve here so that I could look into it further? Thank you.

#define ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
#endif

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