To not consider the current time segment adds unwanted latency in the load/util_avg responsivness especially when the time is scaled instead of the contribution. Instead of waiting for the current time segment to have fully elapsed before accounting it in load/util_avg, we can already account the elapsed part but change the range used to compute load/util_avg accordingly. At the very beginning of a new time segment, the past segments have been decayed and the max value is MAX_LOAD_AVG*y. At the very end of the current time segment, the max value becomes 1024(us) + MAX_LOAD_AVG*y which is equal to MAX_LOAD_AVG. In fact, the max value is sa->period_contrib + MAX_LOAD_AVG*y at any time in the time segment.
Taking advantage of the fact that MAX_LOAD_AVG*y == MAX_LOAD_AVG-1024, the range becomes [0..MAX_LOAD_AVG-1024+sa->period_contrib]. As the elapsed part is already accounted in load/util_sum, we update the max value according to the current position in the time segment instead of removing its contribution. Signed-off-by: Vincent Guittot <[email protected]> --- kernel/sched/fair.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index f74da94..c3b8f0f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3017,15 +3017,12 @@ ___update_load_avg(u64 now, int cpu, struct sched_avg *sa, /* * Step 2: update *_avg. */ - sa->load_avg = div_u64((sa->load_sum - sa->period_contrib * weight), - (LOAD_AVG_MAX - 1024)); + sa->load_avg = div_u64(sa->load_sum, LOAD_AVG_MAX - 1024 + sa->period_contrib); if (cfs_rq) { cfs_rq->runnable_load_avg = - div_u64((cfs_rq->runnable_load_sum - sa->period_contrib * weight), - (LOAD_AVG_MAX - 1024)); + div_u64(cfs_rq->runnable_load_sum, LOAD_AVG_MAX - 1024 + sa->period_contrib); } - sa->util_avg = (sa->util_sum - (running * sa->period_contrib << SCHED_CAPACITY_SHIFT)) / - (LOAD_AVG_MAX - 1024); + sa->util_avg = sa->util_sum / (LOAD_AVG_MAX - 1024 + sa->period_contrib); return 1; } -- 2.7.4
