Messages in this thread | | | Date | Tue, 28 Jun 2022 20:32:56 +0800 | Subject | Re: [PATCH v4] sched/fair: combine detach into dequeue when migrating task | From | Chengming Zhou <> |
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Hello, friendly ping...
Thanks.
On 2022/6/20 21:36, Chengming Zhou wrote: > 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() > -> propagate_entity_cfs_rq() call in 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. > > Copied from Dietmar's much clearer comment: > > detach_task() > deactivate_task() > dequeue_task_fair() > for_each_sched_entity(se) > dequeue_entity() > update_load_avg() /* (1) */ > > set_task_cpu() > migrate_task_rq_fair() > /* called detach_entity_cfs_rq() before the patch (2) */ > > This patch save the propagate_entity_cfs_rq(&p->se) call from (2) > by doing the detach_entity_load_avg(), update_tg_load_avg() for > a migrating task inside (1) (the task being the first se in the loop) > > Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> > --- > 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
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