From 9e0bc7c1e84d7fffb93130f2b7d079a0853329ed Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas <heikki.linnakangas@iki.fi> Date: Fri, 28 Jun 2013 12:30:55 +0300 Subject: [PATCH] Track spinlock delay in microsecond granularity. On many platforms the OS will round the sleep time to millisecond resolution, but there is no reason for us to pre-emptively round the argument to pg_usleep. When the delay was measured in milliseconds and started from 1 ms, it sometimes took many attempts until the logic that increases the delay by multiplying with a random value between 1 and 2 actually managed to bump it from 1 ms to 2 ms. That lead to a sequence of 1 ms waits until the delay started to increase. This wasn't really a problem but it looked odd if you observed the waits. There is no measurable difference in performance, but it's more readable this way. Jeff Janes --- src/backend/storage/lmgr/s_lock.c | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-) diff --git a/src/backend/storage/lmgr/s_lock.c b/src/backend/storage/lmgr/s_lock.c index ed1f56aa8b6..940b6865d24 100644 --- a/src/backend/storage/lmgr/s_lock.c +++ b/src/backend/storage/lmgr/s_lock.c @@ -81,17 +81,12 @@ s_lock(volatile slock_t *lock, const char *file, int line) * so minutes. It seems better to fix the total number of tries (and thus * the probability of unintended failure) than to fix the total time * spent. - * - * The pg_usleep() delays are measured in milliseconds because 1 msec is a - * common resolution limit at the OS level for newer platforms. On older - * platforms the resolution limit is usually 10 msec, in which case the - * total delay before timeout will be a bit more. */ #define MIN_SPINS_PER_DELAY 10 #define MAX_SPINS_PER_DELAY 1000 #define NUM_DELAYS 1000 -#define MIN_DELAY_MSEC 1 -#define MAX_DELAY_MSEC 1000 +#define MIN_DELAY_USEC 1000L +#define MAX_DELAY_USEC 1000000L int spins = 0; int delays = 0; @@ -109,9 +104,9 @@ s_lock(volatile slock_t *lock, const char *file, int line) s_lock_stuck(lock, file, line); if (cur_delay == 0) /* first time to delay? */ - cur_delay = MIN_DELAY_MSEC; + cur_delay = MIN_DELAY_USEC; - pg_usleep(cur_delay * 1000L); + pg_usleep(cur_delay); #if defined(S_LOCK_TEST) fprintf(stdout, "*"); @@ -122,8 +117,8 @@ s_lock(volatile slock_t *lock, const char *file, int line) cur_delay += (int) (cur_delay * ((double) random() / (double) MAX_RANDOM_VALUE) + 0.5); /* wrap back to minimum delay when max is exceeded */ - if (cur_delay > MAX_DELAY_MSEC) - cur_delay = MIN_DELAY_MSEC; + if (cur_delay > MAX_DELAY_USEC) + cur_delay = MIN_DELAY_USEC; spins = 0; } -- GitLab