Subrata Modak wrote: > On Thu, 2009-06-25 at 09:46 +0530, gowrishankar wrote: >> 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]> >>> > > Thanks Darren. Long time LTP say updates to RT tests. What happened to > the RT-Graphics tests that probably were in the pipeline ?
Hrm.... well.... I can't recall what those might have been. The only graphics testing we do is really just functional testing using existing tests like x11perf and specviewperf. We haven't written anything specifically for -rt. Do you have any more detail on what this might have been? -- Darren > > Regards-- > Subrata > >> 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); > -- Darren Hart IBM Linux Technology Center Real-Time Linux Team ------------------------------------------------------------------------------ _______________________________________________ Ltp-list mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/ltp-list
