Messages in this thread | | | Date | Wed, 29 Jun 2022 09:37:54 +0800 | Subject | Re: [External] Re: [PATCH v4] sched/fair: combine detach into dequeue when migrating task | From | Chengming Zhou <> |
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Hi, thanks for your review.
On 2022/6/28 23:26, Vincent Guittot wrote: > On Mon, 20 Jun 2022 at 15:36, Chengming Zhou > <zhouchengming@bytedance.com> 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. >> -> propagate_entity_cfs_rq() call in detach_entity_cfs_rq() in >> migrate_task_rq_fair(). >> >> >> 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: > > Although It's nice to keep the author of a comment, it should not be > part of the commit message.
Ok, I will delete this.
> >> 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() > > Could you add the full call stack so we can see more easily the extra > loop that is saved
Good advice, I will add it.
Thanks.
>> >> 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> > > Apart the small nit above: > > Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> > >> --- >> 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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