From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754646AbcEXIKS (ORCPT ); Tue, 24 May 2016 04:10:18 -0400 Received: from foss.arm.com ([217.140.101.70]:55299 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751781AbcEXIKP (ORCPT ); Tue, 24 May 2016 04:10:15 -0400 Date: Tue, 24 May 2016 09:10:55 +0100 From: Morten Rasmussen To: Yuyang Du Cc: peterz@infradead.org, mingo@redhat.com, dietmar.eggemann@arm.com, vincent.guittot@linaro.org, mgalbraith@suse.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH 09/16] sched/fair: Let asymmetric cpu configurations balance at wake-up Message-ID: <20160524081054.GE27946@e105550-lin.cambridge.arm.com> References: <1464001138-25063-1-git-send-email-morten.rasmussen@arm.com> <1464001138-25063-10-git-send-email-morten.rasmussen@arm.com> <20160524000424.GF18670@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160524000424.GF18670@intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 24, 2016 at 08:04:24AM +0800, Yuyang Du wrote: > On Mon, May 23, 2016 at 11:58:51AM +0100, 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 the cpu capacities > > available within the SD_WAKE_AFFINE sched_domain. If not, let wakeup > > balancing take over (find_idlest_{group, cpu}()). > > > > The assumption is that SD_WAKE_AFFINE is never set for a sched_domain > > containing cpus with different capacities. This is enforced by a > > previous patch based on the SD_ASYM_CPUCAPACITY flag. > > > > 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 564215d..ce44fa7 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; > > @@ -5293,6 +5299,25 @@ 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 delta; > > + long prev_cap = capacity_of(prev_cpu); > > + > > + delta = cpu_rq(cpu)->rd->max_cpu_capacity - prev_cap; > > + > > + /* prev_cpu is fairly close to max, no need to abort wake_affine */ > > + if (delta < prev_cap >> 3) > > + return 0; > > delta can be negative? still return 0? I could add an abs() around delta. Do you have a specific scenario in mind? Under normal circumstances, I don't think it can be negative?