From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932651AbdJ3RVC (ORCPT ); Mon, 30 Oct 2017 13:21:02 -0400 Received: from merlin.infradead.org ([205.233.59.134]:36470 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932631AbdJ3RU6 (ORCPT ); Mon, 30 Oct 2017 13:20:58 -0400 Date: Mon, 30 Oct 2017 18:20:35 +0100 From: Peter Zijlstra To: Vincent Guittot Cc: Ingo Molnar , linux-kernel , Tejun Heo , Josef Bacik , Linus Torvalds , Mike Galbraith , Paul Turner , Chris Mason , Dietmar Eggemann , Morten Rasmussen , Ben Segall , Yuyang Du Subject: Re: [PATCH -v2 12/18] sched/fair: Rewrite PELT migration propagation Message-ID: <20171030172035.2edzqvth7v5zki75@hirez.programming.kicks-ass.net> References: <20170901132059.342024223@infradead.org> <20170901132748.580255511@infradead.org> <20171010072945.rjeuripvfksfpdcf@hirez.programming.kicks-ass.net> <20171013152254.GA7393@linaro.org> <20171013204111.GB6524@worktop.programming.kicks-ass.net> <20171016135501.GA11688@linaro.org> <20171019150442.GA25025@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171019150442.GA25025@linaro.org> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org So after a bit of poking I ended up with something like the below; I think there's still a few open points, see XXX. But its better than we have now. Josef, could you see if this completely wrecks your workloads? --- Subject: sched: Update runnable propagation rule From: Vincent Guittot Date: Thu, 19 Oct 2017 17:04:42 +0200 Unlike running, the runnable part can't be directly propagated through the hierarchy when we migrate a task. The main reason is that runnable time can be shared with other sched_entities that stay on the rq and this runnable time will also remain on prev cfs_rq and must not be removed. Instead, we can estimate what should be the new runnable of the prev cfs_rq and check that this estimation stay in a possible range. The prop_runnable_sum is a good estimation when adding runnable_sum but fails most often when we remove it. Instead, we could use the formula below instead: gcfs_rq's runnable_sum = gcfs_rq->avg.load_sum / gcfs_rq->load.weight which assumes that tasks are equally runnable which is not true but easy to compute. Beside these estimates, we have several simple rules that help us to filter out wrong ones: - ge->avg.runnable_sum <= than LOAD_AVG_MAX - ge->avg.runnable_sum >= ge->avg.running_sum (ge->avg.util_sum << LOAD_AVG_MAX) - ge->avg.runnable_sum can't increase when we detach a task Cc: Yuyang Du Cc: Ingo Molnar Cc: Mike Galbraith Cc: Chris Mason Cc: Linus Torvalds Cc: Dietmar Eggemann Cc: Josef Bacik Cc: Ben Segall Cc: Paul Turner Cc: Tejun Heo Cc: Morten Rasmussen Signed-off-by: Vincent Guittot Signed-off-by: Peter Zijlstra (Intel) Link: http://lkml.kernel.org/r/20171019150442.GA25025@linaro.org --- kernel/sched/fair.c | 99 ++++++++++++++++++++++++++++++++++++---------------- 1 file changed, 70 insertions(+), 29 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3412,9 +3412,9 @@ void set_task_rq_fair(struct sched_entit * _IFF_ we look at the pure running and runnable sums. Because they * represent the very same entity, just at different points in the hierarchy. * - * - * Per the above update_tg_cfs_util() is trivial (and still 'wrong') and - * simply copies the running sum over. + * Per the above update_tg_cfs_util() is trivial and simply copies the running + * sum over (but still wrong, because the group entity and group rq do not have + * their PELT windows aligned). * * However, update_tg_cfs_runnable() is more complex. So we have: * @@ -3423,11 +3423,11 @@ void set_task_rq_fair(struct sched_entit * And since, like util, the runnable part should be directly transferable, * the following would _appear_ to be the straight forward approach: * - * grq->avg.load_avg = grq->load.weight * grq->avg.running_avg (3) + * grq->avg.load_avg = grq->load.weight * grq->avg.runnable_avg (3) * * And per (1) we have: * - * ge->avg.running_avg == grq->avg.running_avg + * ge->avg.runnable_avg == grq->avg.runnable_avg * * Which gives: * @@ -3446,27 +3446,28 @@ void set_task_rq_fair(struct sched_entit * to (shortly) return to us. This only works by keeping the weights as * integral part of the sum. We therefore cannot decompose as per (3). * - * OK, so what then? + * Another reason this doesn't work is that runnable isn't a 0-sum entity. + * Imagine a rq with 2 tasks that each are runnable 2/3 of the time. Then the + * rq itself is runnable anywhere between 2/3 and 1 depending on how the + * runnable section of these tasks overlap (or not). If they were to perfectly + * align the rq as a whole would be runnable 2/3 of the time. If however we + * always have at least 1 runnable task, the rq as a whole is always runnable. * + * So we'll have to approximate.. :/ * - * Another way to look at things is: + * Given the constraint: * - * grq->avg.load_avg = \Sum se->avg.load_avg + * ge->avg.running_sum <= ge->avg.runnable_sum <= LOAD_AVG_MAX * - * Therefore, per (2): + * We can construct a rule that adds runnable to a rq by assuming minimal + * overlap. * - * grq->avg.load_avg = \Sum se->load.weight * se->avg.runnable_avg + * On removal, we'll assume each task is equally runnable; which yields: * - * And the very thing we're propagating is a change in that sum (someone - * joined/left). So we can easily know the runnable change, which would be, per - * (2) the already tracked se->load_avg divided by the corresponding - * se->weight. + * grq->avg.runnable_sum = grq->avg.load_sum / grq->load.weight * - * Basically (4) but in differential form: + * XXX: only do this for the part of runnable > running ? * - * d(runnable_avg) += se->avg.load_avg / se->load.weight - * (5) - * ge->avg.load_avg += ge->load.weight * d(runnable_avg) */ static inline void @@ -3478,6 +3479,14 @@ update_tg_cfs_util(struct cfs_rq *cfs_rq if (!delta) return; + /* + * The relation between sum and avg is: + * + * LOAD_AVG_MAX - 1024 + sa->period_contrib + * + * however, the PELT windows are not aligned between grq and gse. + */ + /* Set new sched_entity's utilization */ se->avg.util_avg = gcfs_rq->avg.util_avg; se->avg.util_sum = se->avg.util_avg * LOAD_AVG_MAX; @@ -3490,33 +3499,65 @@ update_tg_cfs_util(struct cfs_rq *cfs_rq static inline void update_tg_cfs_runnable(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq *gcfs_rq) { - long runnable_sum = gcfs_rq->prop_runnable_sum; - long runnable_load_avg, load_avg; - s64 runnable_load_sum, load_sum; + long delta_avg, running_sum, runnable_sum = gcfs_rq->prop_runnable_sum; + unsigned long runnable_load_avg, load_avg; + u64 runnable_load_sum, load_sum = 0; + s64 delta_sum; if (!runnable_sum) return; gcfs_rq->prop_runnable_sum = 0; + if (runnable_sum >= 0) { + /* + * Add runnable; clip at LOAD_AVG_MAX. Reflects that until + * the CPU is saturated running == runnable. + */ + runnable_sum += se->avg.load_sum; + runnable_sum = min(runnable_sum, (long)LOAD_AVG_MAX); + } else { + /* + * Estimate the departing task's runnable by assuming all tasks + * are equally runnable. + * + * XXX: doesn't deal with multiple departures? + */ + if (scale_load_down(gcfs_rq->load.weight)) { + load_sum = div_s64(gcfs_rq->avg.load_sum, + scale_load_down(gcfs_rq->load.weight)); + } + + /* But make sure to not inflate se's runnable */ + runnable_sum = min(se->avg.load_sum, load_sum); + } + + /* runnable_sum can't be lower than running_sum */ + running_sum = se->avg.util_sum >> SCHED_CAPACITY_SHIFT; /* XXX ? */ + runnable_sum = max(runnable_sum, running_sum); + load_sum = (s64)se_weight(se) * runnable_sum; load_avg = div_s64(load_sum, LOAD_AVG_MAX); - add_positive(&se->avg.load_sum, runnable_sum); - add_positive(&se->avg.load_avg, load_avg); + delta_sum = load_sum - (s64)se_weight(se) * se->avg.load_sum; + delta_avg = load_avg - se->avg.load_avg; - add_positive(&cfs_rq->avg.load_avg, load_avg); - add_positive(&cfs_rq->avg.load_sum, load_sum); + se->avg.load_sum = runnable_sum; + se->avg.load_avg = load_avg; + add_positive(&cfs_rq->avg.load_avg, delta_avg); + add_positive(&cfs_rq->avg.load_sum, delta_sum); runnable_load_sum = (s64)se_runnable(se) * runnable_sum; runnable_load_avg = div_s64(runnable_load_sum, LOAD_AVG_MAX); + delta_sum = runnable_load_sum - se_weight(se) * se->avg.runnable_load_sum; + delta_avg = runnable_load_avg - se->avg.runnable_load_avg; - add_positive(&se->avg.runnable_load_sum, runnable_sum); - add_positive(&se->avg.runnable_load_avg, runnable_load_avg); + se->avg.runnable_load_sum = runnable_sum; + se->avg.runnable_load_avg = runnable_load_avg; if (se->on_rq) { - add_positive(&cfs_rq->avg.runnable_load_avg, runnable_load_avg); - add_positive(&cfs_rq->avg.runnable_load_sum, runnable_load_sum); + add_positive(&cfs_rq->avg.runnable_load_avg, delta_avg); + add_positive(&cfs_rq->avg.runnable_load_sum, delta_sum); } }