[RFC/PATCH v4 1/3] add high resolution timer function to debug performance issues
- From
Karsten Blees <karsten.blees@gmail.com>
- Date
- May 20, 2014, 19:11 UTC
- Message-ID
- <537BA8D1.1090503@gmail.com>
- In-Reply-To
- <537BA806.50600@gmail.com>
Add a getnanotime() function that returns nanoseconds since 01/01/1970 as unsigned 64-bit integer (i.e. overflows in july 2554). This is easier to work with than e.g. struct timeval or struct timespec.
The implementation uses gettimeofday() by default; supports high precision time sources on the following platforms: * Linux: using clock_gettime(CLOCK_MONOTONIC) * Windows: using QueryPerformanceCounter()
Todo: * enable clock_gettime() on more platforms * implement Mac OSX version using mach_absolute_time
Signed-off-by: Karsten Blees <blees@dcon.de> --- Makefile | 7 +++++ cache.h | 1 + config.mak.uname | 1 + trace.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 91 insertions(+)
diff --git a/Makefile b/Makefile index a53f3a8..3c05f8c 100644 --- a/Makefile +++ b/Makefile @@ -341,6 +341,8 @@ all:: # # Define GMTIME_UNRELIABLE_ERRORS if your gmtime() function does not # return NULL when it receives a bogus time_t. +# +# Define HAVE_CLOCK_GETTIME if your platform has clock_gettime in librt. GIT-VERSION-FILE: FORCE @$(SHELL_PATH) ./GIT-VERSION-GEN @@ -1497,6 +1499,11 @@ ifdef GMTIME_UNRELIABLE_ERRORS BASIC_CFLAGS += -DGMTIME_UNRELIABLE_ERRORS endif +ifdef HAVE_CLOCK_GETTIME + BASIC_CFLAGS += -DHAVE_CLOCK_GETTIME + EXTLIBS += -lrt +endif + ifeq ($(TCLTK_PATH),) NO_TCLTK = NoThanks endif diff --git a/cache.h b/cache.h index 107ac61..48fc616 100644 --- a/cache.h +++ b/cache.h @@ -1362,6 +1362,7 @@ extern int trace_want(const char *key); __attribute__((format (printf, 2, 3))) extern void trace_printf_key(const char *key, const char *fmt, ...); extern void trace_strbuf(const char *key, const struct strbuf *buf); +extern uint64_t getnanotime(void); void packet_trace_identity(const char *prog); diff --git a/config.mak.uname b/config.mak.uname index 23a8803..5e3b1dd 100644 --- a/config.mak.uname +++ b/config.mak.uname @@ -33,6 +33,7 @@ ifeq ($(uname_S),Linux) HAVE_PATHS_H = YesPlease LIBC_CONTAINS_LIBINTL = YesPlease HAVE_DEV_TTY = YesPlease + HAVE_CLOCK_GETTIME = YesPlease endif ifeq ($(uname_S),GNU/kFreeBSD) NO_STRLCPY = YesPlease diff --git a/trace.c b/trace.c index 08180a9..3d72084 100644 --- a/trace.c +++ b/trace.c @@ -187,3 +187,85 @@ int trace_want(const char *key) return 0; return 1; } + +#ifdef HAVE_CLOCK_GETTIME + +static inline uint64_t highres_nanos(void) +{ + struct timespec ts; + if (clock_gettime(CLOCK_MONOTONIC, &ts)) + return 0; + return (uint64_t) ts.tv_sec * 1000000000 + ts.tv_nsec; +} + +#elif defined (GIT_WINDOWS_NATIVE) + +static inline uint64_t highres_nanos(void) +{ + static uint64_t high_ns, scaled_low_ns; + static int scale; + LARGE_INTEGER cnt; + + if (!scale) { + if (!QueryPerformanceFrequency(&cnt)) + return 0; + + /* high_ns = number of ns per cnt.HighPart */ + high_ns = (1000000000LL << 32) / (uint64_t) cnt.QuadPart; + + /* + * Number of ns per cnt.LowPart is 10^9 / frequency (or + * high_ns >> 32). For maximum precision, we scale this factor + * so that it just fits within 32 bit (i.e. won't overflow if + * multiplied with cnt.LowPart). + */ + scaled_low_ns = high_ns; + scale = 32; + while (scaled_low_ns >= 0x100000000LL) { + scaled_low_ns >>= 1; + scale--; + } + } + + /* if QPF worked on initialization, we expect QPC to work as well */ + QueryPerformanceCounter(&cnt); + + return (high_ns * cnt.HighPart) + + ((scaled_low_ns * cnt.LowPart) >> scale); +} + +#else +# define highres_nanos() 0 +#endif + +static inline uint64_t gettimeofday_nanos(void) +{ + struct timeval tv; + gettimeofday(&tv, NULL); + return (uint64_t) tv.tv_sec * 1000000000 + tv.tv_usec * 1000; +} + +/* + * Returns nanoseconds since the epoch (01/01/1970), for performance tracing + * (i.e. favoring high precision over wall clock time accuracy). + */ +inline uint64_t getnanotime(void) +{ + static uint64_t offset; + if (offset > 1) { + /* initialization succeeded, return offset + high res time */ + return offset + highres_nanos(); + } else if (offset == 1) { + /* initialization failed, fall back to gettimeofday */ + return gettimeofday_nanos(); + } else { + /* initialize offset if high resolution timer works */ + uint64_t now = gettimeofday_nanos(); + uint64_t highres = highres_nanos(); + if (highres) + offset = now - highres; + else + offset = 1; + return now; + } +}
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