Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755415AbdLOMDn (ORCPT ); Fri, 15 Dec 2017 07:03:43 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:54860 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755031AbdLOMDj (ORCPT ); Fri, 15 Dec 2017 07:03:39 -0500 Date: Fri, 15 Dec 2017 12:03:31 +0000 From: Patrick Bellasi To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Paul Turner , Dietmar Eggemann , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes Subject: Re: [PATCH v2 2/4] sched/fair: add util_est on top of PELT Message-ID: <20171215120331.GA19821@e110439-lin> References: <20171205171018.9203-1-patrick.bellasi@arm.com> <20171205171018.9203-3-patrick.bellasi@arm.com> <20171213161922.qbxq2ko5q6ttzu2p@hirez.programming.kicks-ass.net> <20171213163653.GD8264@e110439-lin> <20171213170309.5yk62ipzo3ckpw6o@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171213170309.5yk62ipzo3ckpw6o@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6057 Lines: 118 On 13-Dec 18:03, Peter Zijlstra wrote: > On Wed, Dec 13, 2017 at 04:36:53PM +0000, Patrick Bellasi wrote: > > On 13-Dec 17:19, Peter Zijlstra wrote: > > > On Tue, Dec 05, 2017 at 05:10:16PM +0000, Patrick Bellasi wrote: > > > > @@ -562,6 +577,12 @@ struct task_struct { > > > > > > > > const struct sched_class *sched_class; > > > > struct sched_entity se; > > > > + /* > > > > + * Since we use se.avg.util_avg to update util_est fields, > > > > + * this last can benefit from being close to se which > > > > + * also defines se.avg as cache aligned. > > > > + */ > > > > + struct util_est util_est; > > The thing is, since sched_entity has a member with cacheline alignment, > the whole structure must have cacheline alignment, and this util_est > _will_ start on a new line. Right, I was not considering that "aligned" affects also the start of the following data. Thus > See also: > > $ pahole -EC task_struct defconfig/kernel/sched/core.o > > ... > struct sched_avg { > /* typedef u64 */ long long unsigned int last_update_time; /* 576 8 */ > /* typedef u64 */ long long unsigned int load_sum; /* 584 8 */ > /* typedef u32 */ unsigned int util_sum; /* 592 4 */ > /* typedef u32 */ unsigned int period_contrib; /* 596 4 */ > long unsigned int load_avg; /* 600 8 */ > long unsigned int util_avg; /* 608 8 */ > } avg; /* 576 40 */ > /* --- cacheline 6 boundary (384 bytes) --- */ > } se; /* 192 448 */ > /* --- cacheline 8 boundary (512 bytes) was 24 bytes ago --- */ > struct util_est { > long unsigned int last; /* 640 8 */ > long unsigned int ewma; /* 648 8 */ > } util_est; /* 640 16 */ > ... > > The thing is somewhat confused on which cacheline is which, but you'll > see sched_avg landing at 576 (cacheline #9) and util_est at 640 (line > #10). > > > > > struct sched_rt_entity rt; > > > > #ifdef CONFIG_CGROUP_SCHED > > > > struct task_group *sched_task_group; > > > One goal was to keep util_est variables close to the util_avg used to > > load the filter, for caches affinity sakes. > > > > The other goal was to have util_est data only for Tasks and CPU's > > RQ, thus avoiding unused data for TG's RQ and SE. > > > > Unfortunately the first goal does not allow to achieve completely the > > second and, you right, the solution looks a bit inconsistent. > > > > Do you think we should better disregard cache proximity and move > > util_est_runnable to rq? > > proximity is likely important; I'd suggest moving util_est into > sched_entity. So, by moving util_est right after sched_avg, here is what we get (with some lines to better highlight 64B boundaries): const struct sched_class * sched_class; /* 152 8 */ struct sched_entity { [...] ---[ Line 9 ]------------------------------------------------------------------------------- struct sched_avg { /* typedef u64 */ long long unsigned int last_update_time; /* 576 8 */ /* typedef u64 */ long long unsigned int load_sum; /* 584 8 */ /* typedef u64 */ long long unsigned int runnable_load_sum; /* 592 8 */ /* typedef u32 */ unsigned int util_sum; /* 600 4 */ /* typedef u32 */ unsigned int period_contrib; /* 604 4 */ long unsigned int load_avg; /* 608 8 */ long unsigned int runnable_load_avg; /* 616 8 */ long unsigned int util_avg; /* 624 8 */ } avg; /* 576 56 */ /* --- cacheline 6 boundary (384 bytes) was 24 bytes ago --- */ struct util_est { long unsigned int last; /* 632 8 */ ---[ Line 10 ]------------------------------------------------------------------------------ long unsigned int ewma; /* 640 8 */ } util_est; /* 632 16 */ } se; /* 192 512 */ ---[ Line 11 ]------------------------------------------------------------------------------ /* --- cacheline 9 boundary (576 bytes) was 24 bytes ago --- */ struct sched_rt_entity { struct list_head { struct list_head * next; /* 704 8 */ struct list_head * prev; /* 712 8 */ } run_list; /* 704 16 */ As you can see we still end up with util_est spanning acrosss two cache and even worst with an almost empty Line 10. The point is that sched_avg already uses 56B... which leave just 8bytes left. So, I can to move util_est there and use unsigned int for "last" and "ewma" storage. This should fix the cache alignment but only until we do not add other stuff to sched_avg. BTW, should not be possible to use a similar "fasting" approach for load_avg and runnable_load_avg? Given their range a u32 should be just good enough, isn't it? Cheers Patrick -- #include Patrick Bellasi