Messages in this thread Patch in this message | | | Date | Wed, 31 May 2023 13:58:50 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 11/15] sched/eevdf: Better handle mixed slice length |
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In the case where (due to latency-nice) there are different request sizes in the tree, the smaller requests tend to be dominated by the larger. Also note how the EEVDF lag limits are based on r_max.
Therefore; add a heuristic that for the mixed request size case, moves smaller requests to placement strategy #2 which ensures they're immidiately eligible and and due to their smaller (virtual) deadline will cause preemption.
NOTE: this relies on update_entity_lag() to impose lag limits above a single slice.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/sched/fair.c | 30 ++++++++++++++++++++++++++++++ kernel/sched/features.h | 1 + kernel/sched/sched.h | 1 + 3 files changed, 32 insertions(+)
--- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -642,6 +642,7 @@ avg_vruntime_add(struct cfs_rq *cfs_rq, s64 key = entity_key(cfs_rq, se); cfs_rq->avg_vruntime += key * weight; + cfs_rq->avg_slice += se->slice * weight; cfs_rq->avg_load += weight; } @@ -652,6 +653,7 @@ avg_vruntime_sub(struct cfs_rq *cfs_rq, s64 key = entity_key(cfs_rq, se); cfs_rq->avg_vruntime -= key * weight; + cfs_rq->avg_slice -= se->slice * weight; cfs_rq->avg_load -= weight; } @@ -4908,6 +4910,21 @@ static inline void update_misfit_status( #endif /* CONFIG_SMP */ +static inline bool +entity_has_slept(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) +{ + u64 now; + + if (!(flags & ENQUEUE_WAKEUP)) + return false; + + if (flags & ENQUEUE_MIGRATED) + return true; + + now = rq_clock_task(rq_of(cfs_rq)); + return (s64)(se->exec_start - now) >= se->slice; +} + static void place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) { @@ -4930,6 +4947,19 @@ place_entity(struct cfs_rq *cfs_rq, stru lag = se->vlag; /* + * For latency sensitive tasks; those that have a shorter than + * average slice and do not fully consume the slice, transition + * to EEVDF placement strategy #2. + */ + if (sched_feat(PLACE_FUDGE) && + (cfs_rq->avg_slice > se->slice * cfs_rq->avg_load) && + entity_has_slept(cfs_rq, se, flags)) { + lag += vslice; + if (lag > 0) + lag = 0; + } + + /* * If we want to place a task and preserve lag, we have to * consider the effect of the new entity on the weighted * average and compensate for this, otherwise lag can quickly --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -5,6 +5,7 @@ * sleep+wake cycles. EEVDF placement strategy #1, #2 if disabled. */ SCHED_FEAT(PLACE_LAG, true) +SCHED_FEAT(PLACE_FUDGE, true) SCHED_FEAT(PLACE_DEADLINE_INITIAL, true) /* --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -555,6 +555,7 @@ struct cfs_rq { unsigned int idle_h_nr_running; /* SCHED_IDLE */ s64 avg_vruntime; + u64 avg_slice; u64 avg_load; u64 exec_clock;
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