On Thu, Aug 13, 2015 at 06:41:45AM +0800, Yuyang Du wrote: > On Thu, Aug 13, 2015 at 02:55:55PM +0900, byungchul.p...@lge.com wrote: > > > > currently, a task load is synced with its cfs_rq, only when it > > leaves from fair class. we also need to sync it with cfs_rq when > > it returns back to fair class, too. > > Syncing it at the time it is switched to fair is not necessary, because > since last_update_time if it has ever been updated, the load has become > random, IOW, useless. So we simply leave it unattended, and let itself > merge in the system.
hello, i agree with you almost. it would have a meaningless value over time, while it has a meaningful value as soon as it leaved that cfs_rq. however, IMHO, nobody know when a task is switched between sched classes. i think it would be better that we consider that load rather than leave it unattended, even though, of course, in both of cases __update_load_avg() will dacay and fix it over time. shouldn't we consider it? 1. case returning back to fair class very soon: original code cannot reflect the task load to cfs_rq, while patched code can reflect the task load to cfs_rq. 2. case returning back to fair class after long: original code adds 0 to cfs_rq and let __update_load_avg() fix it, while patched code adds a meaningless value to cfs_rq and let __update_load_avg() fix it, afterall these become same. > > > > > #ifdef CONFIG_SMP > > /* synchronize task with its prev cfs_rq */ > > - if (!queued) > > - __update_load_avg(cfs_rq->avg.last_update_time, > > cpu_of(rq_of(cfs_rq)), > > - &se->avg, se->on_rq * > > scale_load_down(se->load.weight), > > - cfs_rq->curr == se, NULL); > > - > > - /* remove our load when we leave */ > > - cfs_rq->avg.load_avg = max_t(long, cfs_rq->avg.load_avg - > > se->avg.load_avg, 0); > > - cfs_rq->avg.load_sum = max_t(s64, cfs_rq->avg.load_sum - > > se->avg.load_sum, 0); > > - cfs_rq->avg.util_avg = max_t(long, cfs_rq->avg.util_avg - > > se->avg.util_avg, 0); > > - cfs_rq->avg.util_sum = max_t(s32, cfs_rq->avg.util_sum - > > se->avg.util_sum, 0); > > + detach_entity_load_avg(cfs_rq, se); > > #endif > > You changed the logic. yes, i changed it. but i think that calling __update_load_avg() is not a problem even in case of "queued == 1". so i didn't think that change seriously. wrong? :( thanks, byungchul > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
