qemu-io-cmds: use clock_gettime for benchmarking
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 <alex.bennee@linaro.org>
diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index 30a7d9a..8904733 100644
--- a/qemu-io-cmds.c
+++ b/qemu-io-cmds.c
@@ -248,20 +248,21 @@
-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 @@
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 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 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 @@
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 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 @@
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 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 @@
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 @@
} 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 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 @@
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 @@
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 @@
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 @@
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 @@
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 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 @@
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));
