Darren Hart wrote: > The current barrier implementation results in the lowest priority thread > actually starting the game (they are the last to be scheduled to call > pthread_barrier_wait). This thread likely gets a priority boost as it > holds > the hb->lock for the futex associated with the barrier. This might lead > to it > running ahead of the defense threads. > In fact, any sort of barrier or cond var implementation (short of a pi > aware > cond broadcast, which is not yet readily available) will result in a > thundering > herd situation when the FUTEX_WAKE_ALL syscall is issued, which can > result in > a short run of one or more offense threads while all the threads get to the > RUNNABLE state. > > This patch removes the complex starting mechansims and replaces them with a > simple atomic counter. All player threads are started and once the > players_ready count reaches the total player count, the referee starts > the game > by setting the ball position to zero. > > Tested on two platforms (both x86_64, 4 and 8-way) for a combined total of > 13,000 iterations with 0 failures. > > Signed-off-by: Darren Hart <[email protected]> >
Acked-by: Gowrishankar <[email protected]> Thanks. Gowri > > Index: ltp/testcases/realtime/func/sched_football/sched_football.c > =================================================================== > --- ltp.orig/testcases/realtime/func/sched_football/sched_football.c > 2009-06-24 11:49:16.000000000 -0700 > +++ ltp/testcases/realtime/func/sched_football/sched_football.c > 2009-06-24 11:48:44.000000000 -0700 > @@ -47,9 +47,11 @@ > * > * HISTORY > * 2006-03-16 Reduced verbosity, non binary failure reporting, > removal of > - * crazy_fans thread, added game_length argument by Darren Hart. > - * 2007-08-01 Remove all thread cleanup in favor of simply > exiting.Various > - * bugfixes and cleanups. -- Josh Triplett > + * crazy_fans thread, added game_length argument by > Darren Hart. > + * 2007-08-01 Remove all thread cleanup in favor of simply > exiting.Various > + * bugfixes and cleanups. -- Josh Triplett > + * 2009-06-23 Simplified atomic startup mechanism, avoiding > thundering herd > + * scheduling at the beginning of the game. -- Darren Hart > * > > *****************************************************************************/ > > > > @@ -71,11 +73,9 @@ > /* Here's the position of the ball */ > volatile int the_ball; > > -/* pthread_barrier for synchronization */ > -pthread_barrier_t barrier; > - > static int players_per_team = 0; > static int game_length = DEF_GAME_LENGTH; > +static atomic_t players_ready; > > void usage(void) > { > @@ -110,8 +110,7 @@ > /* This is the defensive team. They're trying to block the offense */ > void *thread_defense(void* arg) > { > - pthread_barrier_wait(&barrier); > - > + atomic_inc(&players_ready); > /*keep the ball from being moved */ > while (1) { > sched_yield(); /* let other defenders run */ > @@ -123,8 +122,7 @@ > /* This is the offensive team. They're trying to move the ball */ > void *thread_offense(void* arg) > { > - pthread_barrier_wait(&barrier); > - > + atomic_inc(&players_ready); > while (1) { > the_ball++; /* move the ball ahead one yard */ > sched_yield(); /* let other offensive players run */ > @@ -141,9 +139,9 @@ > > gettimeofday(&start, NULL); > now = start; > - the_ball = 0; > > - pthread_barrier_wait(&barrier); > + /* Start the game! */ > + the_ball = 0; > > /* Watch the game */ > while ((now.tv_sec - start.tv_sec) < game_length) { > @@ -169,10 +167,7 @@ > if (players_per_team == 0) > players_per_team = sysconf(_SC_NPROCESSORS_ONLN); > > - if ((i = pthread_barrier_init(&barrier, NULL, players_per_team*2 + > 1))) { > - printf("pthread_barrier_init failed: %s\n", strerror(i)); > - exit(i); > - } > + atomic_set(0, &players_ready); > > printf("Running with: players_per_team=%d game_length=%d\n", > players_per_team, game_length); > @@ -181,13 +176,20 @@ > param.sched_priority = sched_get_priority_min(SCHED_FIFO) + 80; > sched_setscheduler(0, SCHED_FIFO, ¶m); > > - /* Start the offense */ > + /* > + * Start the offense > + * They are lower priority than defense, so they must be started > first. > + */ > priority = 15; > printf("Starting %d offense threads at priority %d\n", > players_per_team, priority); > for (i = 0; i < players_per_team; i++) > create_fifo_thread(thread_offense, NULL, priority); > > + /* Wait for the offense threads to start */ > + while (atomic_get(&players_ready) < players_per_team) > + usleep(100); > + > /* Start the defense */ > priority = 30; > printf("Starting %d defense threads at priority %d\n", > @@ -195,6 +197,10 @@ > for (i = 0; i < players_per_team; i++) > create_fifo_thread(thread_defense, NULL, priority); > > + /* Wait for the defense threads to start */ > + while (atomic_get(&players_ready) < players_per_team * 2) > + usleep(100); > + > /* Ok, everyone is on the field, bring out the ref */ > printf("Starting referee thread\n"); > return referee(game_length); ------------------------------------------------------------------------------ _______________________________________________ Ltp-list mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/ltp-list
