Messages in this thread Patch in this message | | | From | Chengming Zhou <> | Subject | [PATCH v5] sched/fair: combine detach into dequeue when migrating task | Date | Wed, 29 Jun 2022 09:58:34 +0800 |
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When we are migrating task out of the CPU, we can combine detach and propagation into dequeue_entity() to save the detach_entity_cfs_rq() in migrate_task_rq_fair().
This optimization is like combining DO_ATTACH in the enqueue_entity() when migrating task to the CPU.
So we don't have to traverse the CFS tree extra time to do the detach_entity_cfs_rq() -> propagate_entity_cfs_rq() call, which wouldn't be called anymore with this patch's change.
detach_task() deactivate_task() dequeue_task_fair() for_each_sched_entity(se) dequeue_entity() update_load_avg() /* (1) */ detach_entity_load_avg()
set_task_cpu() migrate_task_rq_fair() detach_entity_cfs_rq() /* (2) */ update_load_avg(); detach_entity_load_avg(); propagate_entity_cfs_rq(); for_each_sched_entity() update_load_avg()
This patch save the detach_entity_cfs_rq() called in (2) by doing the detach_entity_load_avg() for a CPU migrating task inside (1) (the task being the first se in the loop)
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> --- v5: - improve the commit message suggested by Vincent.
v4: - change the commit message a little. - remove the forward declaration of detach_entity_cfs_rq() - remove verbose comments in code.
v3: - change to use task_on_rq_migrating() and put Dietmar's much clearer description in the commit message. Thanks!
v2: - fix !CONFIG_SMP build error --- kernel/sched/fair.c | 30 +++++++++++++++++------------- 1 file changed, 17 insertions(+), 13 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8bed75757e65..31d53c11e244 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3931,6 +3931,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s #define UPDATE_TG 0x1 #define SKIP_AGE_LOAD 0x2 #define DO_ATTACH 0x4 +#define DO_DETACH 0x8 /* Update task and its cfs_rq load average */ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) @@ -3948,7 +3949,14 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s decayed = update_cfs_rq_load_avg(now, cfs_rq); decayed |= propagate_entity_load_avg(se); - if (!se->avg.last_update_time && (flags & DO_ATTACH)) { + if (flags & DO_DETACH) { + /* + * DO_DETACH means we're here from dequeue_entity() + * and we are migrating task out of the CPU. + */ + detach_entity_load_avg(cfs_rq, se); + update_tg_load_avg(cfs_rq); + } else if (!se->avg.last_update_time && (flags & DO_ATTACH)) { /* * DO_ATTACH means we're here from enqueue_entity(). @@ -4241,6 +4249,7 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq) #define UPDATE_TG 0x0 #define SKIP_AGE_LOAD 0x0 #define DO_ATTACH 0x0 +#define DO_DETACH 0x0 static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1) { @@ -4460,6 +4469,11 @@ static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq); static void dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) { + int action = UPDATE_TG; + + if (entity_is_task(se) && task_on_rq_migrating(task_of(se))) + action |= DO_DETACH; + /* * Update run-time statistics of the 'current'. */ @@ -4473,7 +4487,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) * - For group entity, update its weight to reflect the new share * of its group cfs_rq. */ - update_load_avg(cfs_rq, se, UPDATE_TG); + update_load_avg(cfs_rq, se, action); se_update_runnable(se); update_stats_dequeue_fair(cfs_rq, se, flags); @@ -6938,8 +6952,6 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) return new_cpu; } -static void detach_entity_cfs_rq(struct sched_entity *se); - /* * Called immediately before a task is migrated to a new CPU; task_cpu(p) and * cfs_rq_of(p) references at time of call are still valid and identify the @@ -6973,15 +6985,7 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) se->vruntime -= min_vruntime; } - if (p->on_rq == TASK_ON_RQ_MIGRATING) { - /* - * In case of TASK_ON_RQ_MIGRATING we in fact hold the 'old' - * rq->lock and can modify state directly. - */ - lockdep_assert_rq_held(task_rq(p)); - detach_entity_cfs_rq(&p->se); - - } else { + if (!task_on_rq_migrating(p)) { /* * We are supposed to update the task to "current" time, then * its up to date and ready to go to new CPU/cfs_rq. But we -- 2.36.1
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