Description:
Innodb uses a busy-wait loop in its mutex implementation. There is an assumption that the total wait time is 20 milliseconds. It should determine the wait time at startup and print it. It could also compute the best number of spins to get a 20 millisecond wait.
On my servers, the total busy wait time is 4 milliseconds, not 20.
How to repeat:
Read the source.
Suggested fix:
Code added to compute and print the spin wait time. This is also displayed in SHOW INNODB STATUS
static void time_spin_delay()
{
struct timeval s, e;
int i;
srv_timed_spin_delay = 0;
if (gettimeofday(&s, NULL))
return;
for (i = 0; i < SYNC_SPIN_ROUNDS; ++i)
ut_delay(ut_rnd_interval(0, srv_spin_wait_delay));
if (gettimeofday(&e, NULL))
return;
srv_timed_spin_delay = mics_diff(&e, &s);
}
/*************************************************************************
Prints counters for work done by srv_master_thread. */
static
void
srv_print_extra(
/*===================*/
FILE *file) /* in: output stream */
{
fprintf(file, "srv_master_thread loops: %lu 1_second, %lu sleeps, "
"%lu 10_second, %lu background, %lu flush\n",
srv_main_1_second_loops, srv_main_sleeps,
srv_main_10_second_loops, srv_main_background_loops,
srv_main_flush_loops);
fprintf(file, "srv_master_thread log flush: %lu sync, %lu async\n",
srv_sync_flush, srv_async_flush);
fprintf(file, "srv_wait_thread_mics %lld microseconds, %.1f seconds\n",
srv_thread_wait_mics,
(double) srv_thread_wait_mics / 1000000.0);
fprintf(file,
"spinlock delay for %d delay %d rounds is %lld mics\n",
srv_spin_wait_delay, SYNC_SPIN_ROUNDS, srv_timed_spin_delay);
}
Description: Innodb uses a busy-wait loop in its mutex implementation. There is an assumption that the total wait time is 20 milliseconds. It should determine the wait time at startup and print it. It could also compute the best number of spins to get a 20 millisecond wait. On my servers, the total busy wait time is 4 milliseconds, not 20. How to repeat: Read the source. Suggested fix: Code added to compute and print the spin wait time. This is also displayed in SHOW INNODB STATUS static void time_spin_delay() { struct timeval s, e; int i; srv_timed_spin_delay = 0; if (gettimeofday(&s, NULL)) return; for (i = 0; i < SYNC_SPIN_ROUNDS; ++i) ut_delay(ut_rnd_interval(0, srv_spin_wait_delay)); if (gettimeofday(&e, NULL)) return; srv_timed_spin_delay = mics_diff(&e, &s); } /************************************************************************* Prints counters for work done by srv_master_thread. */ static void srv_print_extra( /*===================*/ FILE *file) /* in: output stream */ { fprintf(file, "srv_master_thread loops: %lu 1_second, %lu sleeps, " "%lu 10_second, %lu background, %lu flush\n", srv_main_1_second_loops, srv_main_sleeps, srv_main_10_second_loops, srv_main_background_loops, srv_main_flush_loops); fprintf(file, "srv_master_thread log flush: %lu sync, %lu async\n", srv_sync_flush, srv_async_flush); fprintf(file, "srv_wait_thread_mics %lld microseconds, %.1f seconds\n", srv_thread_wait_mics, (double) srv_thread_wait_mics / 1000000.0); fprintf(file, "spinlock delay for %d delay %d rounds is %lld mics\n", srv_spin_wait_delay, SYNC_SPIN_ROUNDS, srv_timed_spin_delay); }