From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO Date: Wed, 22 Aug 2018 11:10:24 +0200 Message-ID: <20180822091024.GU24124@hirez.programming.kicks-ass.net> References: <20180801151958.32590-1-hannes@cmpxchg.org> <20180801151958.32590-9-hannes@cmpxchg.org> <20180803172139.GE2494@hirez.programming.kicks-ass.net> <20180821201115.GB24538@cmpxchg.org> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=YbdDDn0LmMntOvsDynUtkB+mSIAFRIE4RGQzJvC3h5Q=; b=jSiz0SUqgjqtYAL67S8Lqar0i p0b7Y7CW10WpXS0NNVGlBubKM8EeCLv1Jaaou8dQCVTcElzguUN/Qs0+SlAHfcnF/mIHfVGmqsyLT s93/sZxhQwWIwqwVs7MNBaOsFZm5hyd6ROK5gaL2lOBo982Ww+U0YqRMmdSV9UarpPQfzV6XNWn6m 0Nqq20kfiGNXzjtfK3hvjtA3dUXVqMMne8QJ4AijNqnL2KzK8YneUDZ8Yi9wiC2eZE6cOJYRs+rgo SMdhHO15+3XIi073bSguMNAihmCZ709twxhLzv26WYHo5bMKi3vPi+YOwbljVTFkyYzXRxRTHssL2 Content-Disposition: inline In-Reply-To: <20180821201115.GB24538@cmpxchg.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Johannes Weiner Cc: Ingo Molnar , Andrew Morton , Linus Torvalds , Tejun Heo , Suren Baghdasaryan , Daniel Drake , Vinayak Menon , Christopher Lameter , Mike Galbraith , Shakeel Butt , Peter Enderborg , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com On Tue, Aug 21, 2018 at 04:11:15PM -0400, Johannes Weiner wrote: > On Fri, Aug 03, 2018 at 07:21:39PM +0200, Peter Zijlstra wrote: > > On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote: > > > + time = READ_ONCE(groupc->times[s]); > > > + /* > > > + * In addition to already concluded states, we > > > + * also incorporate currently active states on > > > + * the CPU, since states may last for many > > > + * sampling periods. > > > + * > > > + * This way we keep our delta sampling buckets > > > + * small (u32) and our reported pressure close > > > + * to what's actually happening. > > > + */ > > > + if (test_state(groupc->tasks, cpu, s)) { > > > + /* > > > + * We can race with a state change and > > > + * need to make sure the state_start > > > + * update is ordered against the > > > + * updates to the live state and the > > > + * time buckets (groupc->times). > > > + * > > > + * 1. If we observe task state that > > > + * needs to be recorded, make sure we > > > + * see state_start from when that > > > + * state went into effect or we'll > > > + * count time from the previous state. > > > + * > > > + * 2. If the time delta has already > > > + * been added to the bucket, make sure > > > + * we don't see it in state_start or > > > + * we'll count it twice. > > > + * > > > + * If the time delta is out of > > > + * state_start but not in the time > > > + * bucket yet, we'll miss it entirely > > > + * and handle it in the next period. > > > + */ > > > + smp_rmb(); > > > + time += cpu_clock(cpu) - groupc->state_start; > > > + } > > > > As is, groupc->state_start needs a READ_ONCE() above and a WRITE_ONCE() > > below. But like stated earlier, doing an update in scheduler_tick() is > > probably easier. > > I've wrapped these in READ_ONCE/WRITE_ONCE. I just realized, these are u64, so READ_ONCE/WRITE_ONCE will not work correct on 32bit.