From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751444AbcGNNpm (ORCPT ); Thu, 14 Jul 2016 09:45:42 -0400 Received: from mail-lf0-f46.google.com ([209.85.215.46]:36365 "EHLO mail-lf0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751231AbcGNNpj (ORCPT ); Thu, 14 Jul 2016 09:45:39 -0400 MIME-Version: 1.0 In-Reply-To: <20160713161441.GB21816@e105550-lin.cambridge.arm.com> References: <1466615004-3503-1-git-send-email-morten.rasmussen@arm.com> <1466615004-3503-8-git-send-email-morten.rasmussen@arm.com> <20160713161441.GB21816@e105550-lin.cambridge.arm.com> From: Vincent Guittot Date: Thu, 14 Jul 2016 15:45:17 +0200 Message-ID: Subject: Re: [PATCH v2 07/13] sched/fair: Let asymmetric cpu configurations balance at wake-up To: Morten Rasmussen Cc: Peter Zijlstra , "mingo@redhat.com" , Dietmar Eggemann , Yuyang Du , mgalbraith@suse.de, linux-kernel Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13 July 2016 at 18:14, Morten Rasmussen wrote: > On Wed, Jul 13, 2016 at 02:56:41PM +0200, Vincent Guittot wrote: >> On 22 June 2016 at 19:03, Morten Rasmussen wrote: >> > Currently, SD_WAKE_AFFINE always takes priority over wakeup balancing if >> > SD_BALANCE_WAKE is set on the sched_domains. For asymmetric >> > configurations SD_WAKE_AFFINE is only desirable if the waking task's >> > compute demand (utilization) is suitable for all the cpu capacities >> > available within the SD_WAKE_AFFINE sched_domain. If not, let wakeup >> >> instead of "suitable for all the cpu capacities available within the >> SD_WAKE_AFFINE sched_domain", should it be "suitable for local cpu and >> prev cpu" becasue you only check the capacity of these 2 CPUs. > > Good point. I currently make the implicit assumption that capacity of local cpu > and prev cpu represent the capacity for all cpus their SD_WAKE_AFFINE > domains. It breaks if you should choose to have SD_WAKE_AFFINE on a > domain that spans both little and big cpus, as if local/prev cpu happens > to be big we assume that they are all big and let select_idle_sibling() > handle the task placement even for big tasks if local/prev cpu are both > big. Isn't the sd_llc used in select_idle_sibling and not the SD_WAKE_AFFINE domian so if CPUs in the sd_llc are homogeneous, we are safe > > I don't see why anybody would want that kind of setup, but I think the > assumption should still be written down somewhere, either here or in a > comment in wake_cap() or both. > > The next paragraph in the commit message mentions that we actually only > check waker cpu and prev_cpu capacity. Would it be more clear if we > extend that to something like: > > This patch makes affine wake-ups conditional on whether both the waker > cpu and prev_cpu has sufficient capacity for the waking task, or > not, assuming that the cpu capacities within an SD_WAKE_AFFINE > domain are homogeneous. > > Thoughts? > >> >> Other than this comment for the commit message, the patch looks good to me >> Acked-by: Vincent Guittot > > Thanks, > Morten > > >> >> > balancing take over (find_idlest_{group, cpu}()). >> > >> > This patch makes affine wake-ups conditional on whether both the waker >> > cpu and prev_cpu has sufficient capacity for the waking task, or not. >> > >> > It is assumed that the sched_group(s) containing the waker cpu and >> > prev_cpu only contain cpu with the same capacity (homogeneous). >> > >> > Ideally, we shouldn't set 'want_affine' in the first place, but we don't >> > know if SD_BALANCE_WAKE is enabled on the sched_domain(s) until we start >> > traversing them. >> > >> > cc: Ingo Molnar >> > cc: Peter Zijlstra >> > >> > Signed-off-by: Morten Rasmussen >> > --- >> > kernel/sched/fair.c | 28 +++++++++++++++++++++++++++- >> > 1 file changed, 27 insertions(+), 1 deletion(-) >> > >> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> > index 216db302e87d..dba02c7b57b3 100644 >> > --- a/kernel/sched/fair.c >> > +++ b/kernel/sched/fair.c >> > @@ -114,6 +114,12 @@ unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL; >> > unsigned int sysctl_sched_cfs_bandwidth_slice = 5000UL; >> > #endif >> > >> > +/* >> > + * The margin used when comparing utilization with cpu capacity: >> > + * util * 1024 < capacity * margin >> > + */ >> > +unsigned int capacity_margin = 1280; /* ~20% */ >> > + >> > static inline void update_load_add(struct load_weight *lw, unsigned long inc) >> > { >> > lw->weight += inc; >> > @@ -5260,6 +5266,25 @@ static int cpu_util(int cpu) >> > return (util >= capacity) ? capacity : util; >> > } >> > >> > +static inline int task_util(struct task_struct *p) >> > +{ >> > + return p->se.avg.util_avg; >> > +} >> > + >> > +static int wake_cap(struct task_struct *p, int cpu, int prev_cpu) >> > +{ >> > + long min_cap, max_cap; >> > + >> > + min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu)); >> > + max_cap = cpu_rq(cpu)->rd->max_cpu_capacity; >> > + >> > + /* Minimum capacity is close to max, no need to abort wake_affine */ >> > + if (max_cap - min_cap < max_cap >> 3) >> > + return 0; >> > + >> > + return min_cap * 1024 < task_util(p) * capacity_margin; >> > +} >> > + >> > /* >> > * select_task_rq_fair: Select target runqueue for the waking task in domains >> > * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE, >> > @@ -5283,7 +5308,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f >> > >> > if (sd_flag & SD_BALANCE_WAKE) { >> > record_wakee(p); >> > - want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p)); >> > + want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu) >> > + && cpumask_test_cpu(cpu, tsk_cpus_allowed(p)); >> > } >> > >> > rcu_read_lock(); >> > -- >> > 1.9.1 >> >