Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754235AbaGPSx2 (ORCPT ); Wed, 16 Jul 2014 14:53:28 -0400 Received: from mail-pa0-f43.google.com ([209.85.220.43]:50911 "EHLO mail-pa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752643AbaGPSx0 (ORCPT ); Wed, 16 Jul 2014 14:53:26 -0400 From: bsegall@google.com To: Morten Rasmussen Cc: Yuyang Du , "mingo\@redhat.com" , "peterz\@infradead.org" , "linux-kernel\@vger.kernel.org" , "pjt\@google.com" , "arjan.van.de.ven\@intel.com" , "len.brown\@intel.com" , "rafael.j.wysocki\@intel.com" , "alan.cox\@intel.com" , "mark.gross\@intel.com" , "fengguang.wu\@intel.com" , "umgwanakikbuti\@gmail.com" Subject: Re: [PATCH 2/2 v3] sched: Rewrite per entity runnable load average tracking References: <1405475447-7783-1-git-send-email-yuyang.du@intel.com> <1405475447-7783-3-git-send-email-yuyang.du@intel.com> <20140716154614.GP26542@e103034-lin> Date: Wed, 16 Jul 2014 11:53:23 -0700 In-Reply-To: <20140716154614.GP26542@e103034-lin> (Morten Rasmussen's message of "Wed, 16 Jul 2014 16:46:14 +0100") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Morten Rasmussen writes: > On Wed, Jul 16, 2014 at 02:50:47AM +0100, Yuyang Du wrote: > > [...] > >> +/* >> + * Update load_avg of the cfs_rq along with its own se. They should get >> + * synchronized: group se's load_avg is used for task_h_load calc, and >> + * group cfs_rq's load_avg is used for task_h_load (and update_cfs_share >> + * calc). >> + */ >> +static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) >> { >> - long old_contrib = se->avg.load_avg_contrib; >> + int decayed; >> >> - if (entity_is_task(se)) { >> - __update_task_entity_contrib(se); >> - } else { >> - __update_tg_runnable_avg(&se->avg, group_cfs_rq(se)); >> - __update_group_entity_contrib(se); >> + if (atomic_long_read(&cfs_rq->removed_load_avg)) { >> + long r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0); >> + cfs_rq->avg.load_avg = subtract_until_zero(cfs_rq->avg.load_avg, r); >> + r *= LOAD_AVG_MAX; >> + cfs_rq->avg.load_sum = subtract_until_zero(cfs_rq->avg.load_sum, r); >> } >> >> - return se->avg.load_avg_contrib - old_contrib; >> -} >> + decayed = __update_load_avg(now, &cfs_rq->avg, cfs_rq->load.weight); >> +#ifndef CONFIG_64BIT >> + if (cfs_rq->avg.last_update_time != cfs_rq->load_last_update_time_copy) >> + sa_q->last_update_time_copy = sa_q->last_update_time; > > This doesn't build on 32 bit. You need: > > - sa_q->last_update_time_copy = sa_q->last_update_time; > + cfs_rq->load_last_update_time_copy = cfs_rq->avg.last_update_time; > > to make it build. But I'm not convinced that this synchronization is > right. > > First let me say that I'm not an expert on synchronization. It seems to > me that there is nothing preventing reordering of the writes in > __update_load_avg() which sets cfs_rq->avg.last_update_time and the > update of cfs_rq->avg.load_last_update_time_copy. You're correct, this needs to be if(...) { smp_wmb(); copy = time; }, the same as update_min_vruntime. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/