Messages in this thread Patch in this message | | | Date | Fri, 15 Nov 2019 16:12:20 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4] sched/freq: move call to cpufreq_update_util |
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On Fri, Nov 15, 2019 at 02:37:27PM +0100, Vincent Guittot wrote: > On Fri, 15 Nov 2019 at 14:25, Peter Zijlstra <peterz@infradead.org> wrote:
> > Should not all 3 have their windows aligned and thus alway return the > > exact same value? > > rt and dl yes but not irq > > But having aligned window doesn't mean that they will all decay. > One can have been updated just before (during a dequeue as an example) > or at least less than 1ms before
Now, the thing is, if that update happened in sched/rt, then it wouldn't have called cpufreq anyway. And once we're idle longer than a period, they'll all decay at once.
Except indeed that IRQ stuff, which runs out of sync.
That is, I'm just not convinced it matters much if we keep rq->cfs on the list forever (like UP). Because we'll only stop calling when update_blocked_averages() when everything hit 0, and up until that point, we'll get one update per period from rq->cfs.
For good measure we can force an update when @done, at that point we know all 0s.
How is something like this?
--- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 545bcb90b4de..a99ac2aa4a23 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3508,9 +3508,6 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) cfs_rq->load_last_update_time_copy = sa->last_update_time; #endif - if (decayed) - cfs_rq_util_change(cfs_rq, 0); - return decayed; } @@ -3620,8 +3617,12 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s attach_entity_load_avg(cfs_rq, se, SCHED_CPUFREQ_MIGRATION); update_tg_load_avg(cfs_rq, 0); - } else if (decayed && (flags & UPDATE_TG)) - update_tg_load_avg(cfs_rq, 0); + } else if (decayed) { + cfs_rq_util_change(cfs_rq, 0); + + if (flags & UPDATE_TG) + update_tg_load_avg(cfs_rq, 0); + } } #ifndef CONFIG_64BIT @@ -7453,7 +7454,7 @@ static void update_blocked_averages(int cpu) struct cfs_rq *cfs_rq, *pos; const struct sched_class *curr_class; struct rq_flags rf; - bool done = true; + bool done = true, decayed = false; rq_lock_irqsave(rq, &rf); update_rq_clock(rq); @@ -7476,10 +7477,14 @@ static void update_blocked_averages(int cpu) * list_add_leaf_cfs_rq() for details. */ for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos) { + bool last = cfs_rq == &rq->cfs; struct sched_entity *se; - if (update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq)) + if (update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq)) { update_tg_load_avg(cfs_rq, 0); + if (last) + decayed = true; + } /* Propagate pending load changes to the parent, if any: */ se = cfs_rq->tg->se[cpu]; @@ -7490,7 +7495,7 @@ static void update_blocked_averages(int cpu) * There can be a lot of idle CPU cgroups. Don't let fully * decayed cfs_rqs linger on the list. */ - if (cfs_rq_is_decayed(cfs_rq)) + if (!last && cfs_rq_is_decayed(cfs_rq)) list_del_leaf_cfs_rq(cfs_rq); /* Don't need periodic decay once load/util_avg are null */ @@ -7498,6 +7503,9 @@ static void update_blocked_averages(int cpu) done = false; } + if (decayed || done) + cpufreq_update_util(rq, 0); + update_blocked_load_status(rq, !done); rq_unlock_irqrestore(rq, &rf); } @@ -7555,6 +7563,7 @@ static inline void update_blocked_averages(int cpu) struct cfs_rq *cfs_rq = &rq->cfs; const struct sched_class *curr_class; struct rq_flags rf; + bool done, decayed; rq_lock_irqsave(rq, &rf); update_rq_clock(rq); @@ -7568,9 +7577,13 @@ static inline void update_blocked_averages(int cpu) update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class); update_irq_load_avg(rq, 0); - update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq); + decayed = update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq); + done = !(cfs_rq_has_blocked(cfs_rq) || others_have_blocked(rq)); - update_blocked_load_status(rq, cfs_rq_has_blocked(cfs_rq) || others_have_blocked(rq)); + if (decayed || done) + cpufreq_update_util(rq, 0); + + update_blocked_load_status(rq, !done); rq_unlock_irqrestore(rq, &rf); }
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