From 50290c002c045280f8defad911901e16bfb52884 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Alex=20Benn=C3=A9e?= Date: Wed, 29 May 2019 17:16:32 +0100 Subject: [PATCH] qemu-io-cmds: use clock_gettime for benchmarking MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The previous use of gettimeofday() ran into undefined behaviour when we ended up doing a div 0 for a very short operation. This is because gettimeofday only works at the microsecond level as well as being prone to discontinuous jumps in system time. Using clock_gettime with CLOCK_MONOTONIC gives greater precision and alleviates some of the potential problems with time jumping around. We could use CLOCK_MONOTONIC_RAW to avoid being tripped up by NTP and adjtime but that is Linux specific so I decided it would do for now. Signed-off-by: Alex Bennée --- qemu-io-cmds.c | 77 +++++++++++++++++++++++++------------------------- 1 file changed, 38 insertions(+), 39 deletions(-) diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c index 30a7d9a13b..8904733961 100644 --- a/qemu-io-cmds.c +++ b/qemu-io-cmds.c @@ -248,20 +248,21 @@ static void cvtstr(double value, char *str, size_t size) -static struct timeval tsub(struct timeval t1, struct timeval t2) +static struct timespec tsub(struct timespec t1, struct timespec t2) { - t1.tv_usec -= t2.tv_usec; - if (t1.tv_usec < 0) { - t1.tv_usec += 1000000; + t1.tv_nsec -= t2.tv_nsec; + if (t1.tv_nsec < 0) { + t1.tv_nsec += NANOSECONDS_PER_SECOND; t1.tv_sec--; } t1.tv_sec -= t2.tv_sec; return t1; } -static double tdiv(double value, struct timeval tv) +static double tdiv(double value, struct timespec tv) { - return value / ((double)tv.tv_sec + ((double)tv.tv_usec / 1000000.0)); + double seconds = tv.tv_sec + (tv.tv_nsec / 1e9); + return value / seconds; } #define HOURS(sec) ((sec) / (60 * 60)) @@ -274,29 +275,27 @@ enum { VERBOSE_FIXED_TIME = 0x2, }; -static void timestr(struct timeval *tv, char *ts, size_t size, int format) +static void timestr(struct timespec *tv, char *ts, size_t size, int format) { - double usec = (double)tv->tv_usec / 1000000.0; + double frac_sec = tv->tv_nsec / 1e9; if (format & TERSE_FIXED_TIME) { if (!HOURS(tv->tv_sec)) { - snprintf(ts, size, "%u:%02u.%02u", - (unsigned int) MINUTES(tv->tv_sec), - (unsigned int) SECONDS(tv->tv_sec), - (unsigned int) (usec * 100)); + snprintf(ts, size, "%u:%05.2f", + (unsigned int) MINUTES(tv->tv_sec), + SECONDS(tv->tv_sec) + frac_sec); return; } format |= VERBOSE_FIXED_TIME; /* fallback if hours needed */ } if ((format & VERBOSE_FIXED_TIME) || tv->tv_sec) { - snprintf(ts, size, "%u:%02u:%02u.%02u", + snprintf(ts, size, "%u:%02u:%05.2f", (unsigned int) HOURS(tv->tv_sec), (unsigned int) MINUTES(tv->tv_sec), - (unsigned int) SECONDS(tv->tv_sec), - (unsigned int) (usec * 100)); + SECONDS(tv->tv_sec) + frac_sec); } else { - snprintf(ts, size, "0.%04u sec", (unsigned int) (usec * 10000)); + snprintf(ts, size, "%05.2f sec", frac_sec); } } @@ -376,7 +375,7 @@ static void dump_buffer(const void *buffer, int64_t offset, int64_t len) } } -static void print_report(const char *op, struct timeval *t, int64_t offset, +static void print_report(const char *op, struct timespec *t, int64_t offset, int64_t count, int64_t total, int cnt, bool Cflag) { char s1[64], s2[64], ts[64]; @@ -649,7 +648,7 @@ static const cmdinfo_t read_cmd = { static int read_f(BlockBackend *blk, int argc, char **argv) { - struct timeval t1, t2; + struct timespec t1, t2; bool Cflag = false, qflag = false, vflag = false; bool Pflag = false, sflag = false, lflag = false, bflag = false; int c, cnt, ret; @@ -758,13 +757,13 @@ static int read_f(BlockBackend *blk, int argc, char **argv) buf = qemu_io_alloc(blk, count, 0xab); - gettimeofday(&t1, NULL); + clock_gettime(CLOCK_MONOTONIC, &t1); if (bflag) { ret = do_load_vmstate(blk, buf, offset, count, &total); } else { ret = do_pread(blk, buf, offset, count, &total); } - gettimeofday(&t2, NULL); + clock_gettime(CLOCK_MONOTONIC, &t2); if (ret < 0) { printf("read failed: %s\n", strerror(-ret)); @@ -836,7 +835,7 @@ static const cmdinfo_t readv_cmd = { static int readv_f(BlockBackend *blk, int argc, char **argv) { - struct timeval t1, t2; + struct timespec t1, t2; bool Cflag = false, qflag = false, vflag = false; int c, cnt, ret; char *buf; @@ -891,9 +890,9 @@ static int readv_f(BlockBackend *blk, int argc, char **argv) return -EINVAL; } - gettimeofday(&t1, NULL); + clock_gettime(CLOCK_MONOTONIC, &t1); ret = do_aio_readv(blk, &qiov, offset, &total); - gettimeofday(&t2, NULL); + clock_gettime(CLOCK_MONOTONIC, &t2); if (ret < 0) { printf("readv failed: %s\n", strerror(-ret)); @@ -972,7 +971,7 @@ static const cmdinfo_t write_cmd = { static int write_f(BlockBackend *blk, int argc, char **argv) { - struct timeval t1, t2; + struct timespec t1, t2; bool Cflag = false, qflag = false, bflag = false; bool Pflag = false, zflag = false, cflag = false; int flags = 0; @@ -1091,7 +1090,7 @@ static int write_f(BlockBackend *blk, int argc, char **argv) buf = qemu_io_alloc(blk, count, pattern); } - gettimeofday(&t1, NULL); + clock_gettime(CLOCK_MONOTONIC, &t1); if (bflag) { ret = do_save_vmstate(blk, buf, offset, count, &total); } else if (zflag) { @@ -1101,7 +1100,7 @@ static int write_f(BlockBackend *blk, int argc, char **argv) } else { ret = do_pwrite(blk, buf, offset, count, flags, &total); } - gettimeofday(&t2, NULL); + clock_gettime(CLOCK_MONOTONIC, &t2); if (ret < 0) { printf("write failed: %s\n", strerror(-ret)); @@ -1160,7 +1159,7 @@ static const cmdinfo_t writev_cmd = { static int writev_f(BlockBackend *blk, int argc, char **argv) { - struct timeval t1, t2; + struct timespec t1, t2; bool Cflag = false, qflag = false; int flags = 0; int c, cnt, ret; @@ -1213,9 +1212,9 @@ static int writev_f(BlockBackend *blk, int argc, char **argv) return -EINVAL; } - gettimeofday(&t1, NULL); + clock_gettime(CLOCK_MONOTONIC, &t1); ret = do_aio_writev(blk, &qiov, offset, flags, &total); - gettimeofday(&t2, NULL); + clock_gettime(CLOCK_MONOTONIC, &t2); if (ret < 0) { printf("writev failed: %s\n", strerror(-ret)); @@ -1250,15 +1249,15 @@ struct aio_ctx { bool zflag; BlockAcctCookie acct; int pattern; - struct timeval t1; + struct timespec t1; }; static void aio_write_done(void *opaque, int ret) { struct aio_ctx *ctx = opaque; - struct timeval t2; + struct timespec t2; - gettimeofday(&t2, NULL); + clock_gettime(CLOCK_MONOTONIC, &t2); if (ret < 0) { @@ -1288,9 +1287,9 @@ out: static void aio_read_done(void *opaque, int ret) { struct aio_ctx *ctx = opaque; - struct timeval t2; + struct timespec t2; - gettimeofday(&t2, NULL); + clock_gettime(CLOCK_MONOTONIC, &t2); if (ret < 0) { printf("readv failed: %s\n", strerror(-ret)); @@ -1425,7 +1424,7 @@ static int aio_read_f(BlockBackend *blk, int argc, char **argv) return -EINVAL; } - gettimeofday(&ctx->t1, NULL); + clock_gettime(CLOCK_MONOTONIC, &ctx->t1); block_acct_start(blk_get_stats(blk), &ctx->acct, ctx->qiov.size, BLOCK_ACCT_READ); blk_aio_preadv(blk, ctx->offset, &ctx->qiov, 0, aio_read_done, ctx); @@ -1570,7 +1569,7 @@ static int aio_write_f(BlockBackend *blk, int argc, char **argv) return -EINVAL; } - gettimeofday(&ctx->t1, NULL); + clock_gettime(CLOCK_MONOTONIC, &ctx->t1); block_acct_start(blk_get_stats(blk), &ctx->acct, ctx->qiov.size, BLOCK_ACCT_WRITE); @@ -1746,7 +1745,7 @@ static const cmdinfo_t discard_cmd = { static int discard_f(BlockBackend *blk, int argc, char **argv) { - struct timeval t1, t2; + struct timespec t1, t2; bool Cflag = false, qflag = false; int c, ret; int64_t offset, bytes; @@ -1787,9 +1786,9 @@ static int discard_f(BlockBackend *blk, int argc, char **argv) return -EINVAL; } - gettimeofday(&t1, NULL); + clock_gettime(CLOCK_MONOTONIC, &t1); ret = blk_pdiscard(blk, offset, bytes); - gettimeofday(&t2, NULL); + clock_gettime(CLOCK_MONOTONIC, &t2); if (ret < 0) { printf("discard failed: %s\n", strerror(-ret));