From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:56248 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932570AbeEIKq3 (ORCPT ); Wed, 9 May 2018 06:46:29 -0400 Date: Wed, 9 May 2018 12:46:18 +0200 From: Peter Zijlstra To: Johannes Weiner Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, cgroups@vger.kernel.org, Ingo Molnar , Andrew Morton , Tejun Heo , Balbir Singh , Mike Galbraith , Oliver Yang , Shakeel Butt , xxx xxx , Taras Kondratiuk , Daniel Walker , Vinayak Menon , Ruslan Ruslichenko , kernel-team@fb.com Subject: Re: [PATCH 6/7] psi: pressure stall information for CPU, memory, and IO Message-ID: <20180509104618.GP12217@hirez.programming.kicks-ass.net> References: <20180507210135.1823-1-hannes@cmpxchg.org> <20180507210135.1823-7-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20180507210135.1823-7-hannes@cmpxchg.org> Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On Mon, May 07, 2018 at 05:01:34PM -0400, Johannes Weiner wrote: > @@ -2038,6 +2038,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags); > if (task_cpu(p) != cpu) { > wake_flags |= WF_MIGRATED; > + psi_ttwu_dequeue(p); > set_task_cpu(p, cpu); > } > > +static inline void psi_ttwu_dequeue(struct task_struct *p) > +{ > + /* > + * Is the task being migrated during a wakeup? Make sure to > + * deregister its sleep-persistent psi states from the old > + * queue, and let psi_enqueue() know it has to requeue. > + */ > + if (unlikely(p->in_iowait || (p->flags & PF_MEMSTALL))) { > + struct rq_flags rf; > + struct rq *rq; > + int clear = 0; > + > + if (p->in_iowait) > + clear |= TSK_IOWAIT; > + if (p->flags & PF_MEMSTALL) > + clear |= TSK_MEMSTALL; > + > + rq = __task_rq_lock(p, &rf); > + update_rq_clock(rq); > + psi_task_change(p, rq_clock(rq), clear, 0); > + p->sched_psi_wake_requeue = 1; > + __task_rq_unlock(rq, &rf); > + } > +} Yeah, no... not happening. We spend a lot of time to never touch the old rq->lock on wakeups. Mason was the one pushing for that, so he should very well know this. The one cross-cpu atomic (iowait) is already a problem (the whole iowait accounting being useless makes it even worse), adding significant remote prodding is just really bad.