From 647e7cac2d215fb8890f79252d7eaee3d6743d66 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Mon, 15 Oct 2007 17:00:13 +0200 Subject: sched: vslice fixups for non-0 nice levels Make vslice accurate wrt nice levels, and add some comments while we're at it. Signed-off-by: Peter Zijlstra Signed-off-by: Ingo Molnar Reviewed-by: Thomas Gleixner --- kernel/sched_fair.c | 53 ++++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 40 insertions(+), 13 deletions(-) (limited to 'kernel/sched_fair.c') diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 32fd976f856..1f14b56d0d0 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -217,6 +217,15 @@ static inline struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq) * Scheduling class statistics methods: */ + +/* + * The idea is to set a period in which each task runs once. + * + * When there are too many tasks (sysctl_sched_nr_latency) we have to stretch + * this period because otherwise the slices get too small. + * + * p = (nr <= nl) ? l : l*nr/nl + */ static u64 __sched_period(unsigned long nr_running) { u64 period = sysctl_sched_latency; @@ -230,27 +239,45 @@ static u64 __sched_period(unsigned long nr_running) return period; } +/* + * We calculate the wall-time slice from the period by taking a part + * proportional to the weight. + * + * s = p*w/rw + */ static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se) { - u64 period = __sched_period(cfs_rq->nr_running); + u64 slice = __sched_period(cfs_rq->nr_running); - period *= se->load.weight; - do_div(period, cfs_rq->load.weight); + slice *= se->load.weight; + do_div(slice, cfs_rq->load.weight); - return period; + return slice; } -static u64 __sched_vslice(unsigned long nr_running) +/* + * We calculate the vruntime slice. + * + * vs = s/w = p/rw + */ +static u64 __sched_vslice(unsigned long rq_weight, unsigned long nr_running) { - unsigned long period = sysctl_sched_latency; - unsigned long nr_latency = sysctl_sched_nr_latency; + u64 vslice = __sched_period(nr_running); - if (unlikely(nr_running > nr_latency)) - nr_running = nr_latency; + do_div(vslice, rq_weight); - period /= nr_running; + return vslice; +} - return (u64)period; +static u64 sched_vslice(struct cfs_rq *cfs_rq) +{ + return __sched_vslice(cfs_rq->load.weight, cfs_rq->nr_running); +} + +static u64 sched_vslice_add(struct cfs_rq *cfs_rq, struct sched_entity *se) +{ + return __sched_vslice(cfs_rq->load.weight + se->load.weight, + cfs_rq->nr_running + 1); } /* @@ -469,10 +496,10 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) vruntime >>= 1; } } else if (sched_feat(APPROX_AVG) && cfs_rq->nr_running) - vruntime += __sched_vslice(cfs_rq->nr_running)/2; + vruntime += sched_vslice(cfs_rq)/2; if (initial && sched_feat(START_DEBIT)) - vruntime += __sched_vslice(cfs_rq->nr_running + 1); + vruntime += sched_vslice_add(cfs_rq, se); if (!initial) { if (sched_feat(NEW_FAIR_SLEEPERS)) -- cgit v1.2.3