From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755697Ab3GKND2 (ORCPT ); Thu, 11 Jul 2013 09:03:28 -0400 Received: from cantor2.suse.de ([195.135.220.15]:44481 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751866Ab3GKND0 (ORCPT ); Thu, 11 Jul 2013 09:03:26 -0400 Date: Thu, 11 Jul 2013 14:03:22 +0100 From: Mel Gorman To: Peter Zijlstra Cc: Srikar Dronamraju , Ingo Molnar , Andrea Arcangeli , Johannes Weiner , Linux-MM , LKML Subject: Re: [PATCH 08/16] sched: Reschedule task on preferred NUMA node once selected Message-ID: <20130711130322.GC2355@suse.de> References: <1373536020-2799-1-git-send-email-mgorman@suse.de> <1373536020-2799-9-git-send-email-mgorman@suse.de> <20130711123038.GH25631@dyad.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20130711123038.GH25631@dyad.programming.kicks-ass.net> 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 Thu, Jul 11, 2013 at 02:30:38PM +0200, Peter Zijlstra wrote: > On Thu, Jul 11, 2013 at 10:46:52AM +0100, Mel Gorman wrote: > > @@ -829,10 +854,29 @@ static void task_numa_placement(struct task_struct *p) > > } > > } > > > > - /* Update the tasks preferred node if necessary */ > > + /* > > + * Record the preferred node as the node with the most faults, > > + * requeue the task to be running on the idlest CPU on the > > + * preferred node and reset the scanning rate to recheck > > + * the working set placement. > > + */ > > if (max_faults && max_nid != p->numa_preferred_nid) { > > + int preferred_cpu; > > + > > + /* > > + * If the task is not on the preferred node then find the most > > + * idle CPU to migrate to. > > + */ > > + preferred_cpu = task_cpu(p); > > + if (cpu_to_node(preferred_cpu) != max_nid) { > > + preferred_cpu = find_idlest_cpu_node(preferred_cpu, > > + max_nid); > > + } > > + > > + /* Update the preferred nid and migrate task if possible */ > > p->numa_preferred_nid = max_nid; > > p->numa_migrate_seq = 0; > > + migrate_task_to(p, preferred_cpu); > > } > > } > > Now what happens if the migrations fails? We set numa_preferred_nid to max_nid > but then never re-try the migration. Should we not re-try the migration every > so often, regardless of whether max_nid changed? We do this load_balance -> active_load_balance_cpu_stop -> move_one_task -> can_migrate_task -> migrate_improves_locality If the conditions are right then it'll move the task to the preferred node for a number of PTE scans. Of course there is no guarantee that the necessary conditions will occur but I was wary of taking more drastic steps in the scheduler such as retrying on every fault until the migration succeeds. -- Mel Gorman SUSE Labs