[flang-commits] [flang] [Flang][runtime] Distinguish CPU time and elapsed time for cpu_time and system_clock (PR #96652)
Michael Klemm via flang-commits
flang-commits at lists.llvm.org
Wed Jun 26 05:06:46 PDT 2024
https://github.com/mjklemm updated https://github.com/llvm/llvm-project/pull/96652
>From bc31456640341e8e6b2a05ab8c1b5d303e7c107a Mon Sep 17 00:00:00 2001
From: Michael Klemm <michael.klemm at amd.com>
Date: Tue, 25 Jun 2024 16:48:22 +0200
Subject: [PATCH 1/2] Distinguish CPU time and elapsed time
---
flang/runtime/time-intrinsic.cpp | 39 ++++++++++++++++++++------------
1 file changed, 24 insertions(+), 15 deletions(-)
diff --git a/flang/runtime/time-intrinsic.cpp b/flang/runtime/time-intrinsic.cpp
index a141fe63764a7..2b2c8a3c34e4d 100644
--- a/flang/runtime/time-intrinsic.cpp
+++ b/flang/runtime/time-intrinsic.cpp
@@ -64,20 +64,29 @@ template <typename Unused = void> double GetCpuTime(fallback_implementation) {
// clock_gettime is implemented in the pthread library for MinGW.
// Using it here would mean that all programs that link libFortranRuntime are
// required to also link to pthread. Instead, don't use the function.
-#undef CLOCKID
-#elif defined CLOCK_PROCESS_CPUTIME_ID
-#define CLOCKID CLOCK_PROCESS_CPUTIME_ID
+#undef CLOCKID_CPU_TIME
+#undef CLOCKID_ELAPSED_TIME
+#else
+// Determine what clock to use for CPU time.
+#if defined CLOCK_PROCESS_CPUTIME_ID
+#define CLOCKID_CPU_TIME CLOCK_PROCESS_CPUTIME_ID
#elif defined CLOCK_THREAD_CPUTIME_ID
-#define CLOCKID CLOCK_THREAD_CPUTIME_ID
-#elif defined CLOCK_MONOTONIC
-#define CLOCKID CLOCK_MONOTONIC
+#define CLOCKID_CPU_TIME CLOCK_THREAD_CPUTIME_ID
+#else
+#undef CLOCKID_CPU_TIME
+#endif
+
+// Determine what clock to use for elapsed time.
+#if defined CLOCK_MONOTONIC
+#define CLOCKID_ELAPSED_TIME CLOCK_MONOTONIC
#elif defined CLOCK_REALTIME
-#define CLOCKID CLOCK_REALTIME
+#define CLOCKID_ELAPSED_TIME CLOCK_REALTIME
#else
-#undef CLOCKID
+#undef CLOCKID_ELAPSED_TIME
+#endif
#endif
-#ifdef CLOCKID
+#ifdef CLOCKID_CPU_TIME
// POSIX implementation using clock_gettime. This is only enabled where
// clock_gettime is available.
template <typename T = int, typename U = struct timespec>
@@ -86,13 +95,13 @@ double GetCpuTime(preferred_implementation,
T ClockId = 0, U *Timespec = nullptr,
decltype(clock_gettime(ClockId, Timespec)) *Enabled = nullptr) {
struct timespec tspec;
- if (clock_gettime(CLOCKID, &tspec) == 0) {
+ if (clock_gettime(CLOCKID_CPU_TIME, &tspec) == 0) {
return tspec.tv_nsec * 1.0e-9 + tspec.tv_sec;
}
// Return some negative value to represent failure.
return -1.0;
}
-#endif
+#endif // CLOCKID_CPU_TIME
using count_t = std::int64_t;
using unsigned_count_t = std::uint64_t;
@@ -149,15 +158,15 @@ constexpr unsigned_count_t DS_PER_SEC{10u};
constexpr unsigned_count_t MS_PER_SEC{1'000u};
constexpr unsigned_count_t NS_PER_SEC{1'000'000'000u};
-#ifdef CLOCKID
+#ifdef CLOCKID_ELAPSED_TIME
template <typename T = int, typename U = struct timespec>
count_t GetSystemClockCount(int kind, preferred_implementation,
// We need some dummy parameters to pass to decltype(clock_gettime).
T ClockId = 0, U *Timespec = nullptr,
- decltype(clock_gettime(ClockId, Timespec)) *Enabled = nullptr) {
+ decltype(clock_gettime(ClockId, Timespec)) *Enabled = nullptr) {
struct timespec tspec;
const unsigned_count_t huge{GetHUGE(kind)};
- if (clock_gettime(CLOCKID, &tspec) != 0) {
+ if (clock_gettime(CLOCKID_ELAPSED_TIME, &tspec) != 0) {
return -huge; // failure
}
unsigned_count_t sec{static_cast<unsigned_count_t>(tspec.tv_sec)};
@@ -170,7 +179,7 @@ count_t GetSystemClockCount(int kind, preferred_implementation,
return (sec * DS_PER_SEC + (nsec / (NS_PER_SEC / DS_PER_SEC))) % (huge + 1);
}
}
-#endif
+#endif // CLOCKID_ELAPSED_TIME
template <typename T = int, typename U = struct timespec>
count_t GetSystemClockCountRate(int kind, preferred_implementation,
>From 9ec6a00340b0b9083fe1a63e2b4331d9e7c11f40 Mon Sep 17 00:00:00 2001
From: Michael Klemm <michael.klemm at amd.com>
Date: Wed, 26 Jun 2024 14:06:31 +0200
Subject: [PATCH 2/2] Rework fallback implementation to use C++11 high-res
clock
---
flang/runtime/time-intrinsic.cpp | 19 ++++++-------------
1 file changed, 6 insertions(+), 13 deletions(-)
diff --git a/flang/runtime/time-intrinsic.cpp b/flang/runtime/time-intrinsic.cpp
index 2b2c8a3c34e4d..f8ea2e3e4d2d1 100644
--- a/flang/runtime/time-intrinsic.cpp
+++ b/flang/runtime/time-intrinsic.cpp
@@ -22,6 +22,7 @@
#ifdef _WIN32
#include "flang/Common/windows-include.h"
#else
+#include <chrono>
#include <sys/time.h> // gettimeofday
#include <sys/times.h>
#include <unistd.h>
@@ -114,26 +115,18 @@ static constexpr inline unsigned_count_t GetHUGE(int kind) {
return (unsigned_count_t{1} << ((8 * kind) - 1)) - 1;
}
-// This is the fallback implementation, which should work everywhere. Note that
-// in general we can't recover after std::clock has reached its maximum value.
+// This is the fallback implementation, which should work everywhere.
template <typename Unused = void>
count_t GetSystemClockCount(int kind, fallback_implementation) {
- std::clock_t timestamp{std::clock()};
- if (timestamp == static_cast<std::clock_t>(-1)) {
+ unsigned_count_t timestamp;
+ timestamp = std::chrono::high_resolution_clock::now().time_since_epoch().count();
+ if (timestamp == static_cast<unsigned_count_t>(-1)) {
// Return -HUGE(COUNT) to represent failure.
return -static_cast<count_t>(GetHUGE(kind));
}
- // Convert the timestamp to std::uint64_t with wrap-around. The timestamp is
- // most likely a floating-point value (since C'11), so compute the modulus
- // carefully when one is required.
- constexpr auto maxUnsignedCount{std::numeric_limits<unsigned_count_t>::max()};
- if constexpr (std::numeric_limits<std::clock_t>::max() > maxUnsignedCount) {
- timestamp -= maxUnsignedCount * std::floor(timestamp / maxUnsignedCount);
- }
- unsigned_count_t unsignedCount{static_cast<unsigned_count_t>(timestamp)};
// Return the modulus of the unsigned integral count with HUGE(COUNT)+1.
// The result is a signed integer but never negative.
- return static_cast<count_t>(unsignedCount % (GetHUGE(kind) + 1));
+ return static_cast<count_t>(timestamp % (GetHUGE(kind) + 1));
}
template <typename Unused = void>
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