From: Mel Gorman <mgorman@suse.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 08/16] sched: Reschedule task on preferred NUMA node once selected
Date: Thu, 11 Jul 2013 14:03:22 +0100 [thread overview]
Message-ID: <20130711130322.GC2355@suse.de> (raw)
In-Reply-To: <20130711123038.GH25631@dyad.programming.kicks-ass.net>
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
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next prev parent reply other threads:[~2013-07-11 13:03 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-11 9:46 [PATCH 0/16] Basic scheduler support for automatic NUMA balancing V4 Mel Gorman
2013-07-11 9:46 ` [PATCH 01/16] mm: numa: Document automatic NUMA balancing sysctls Mel Gorman
2013-07-11 9:46 ` [PATCH 02/16] sched: Track NUMA hinting faults on per-node basis Mel Gorman
2013-07-11 9:46 ` [PATCH 03/16] mm: numa: Account for THP numa hinting faults on the correct node Mel Gorman
2013-07-11 9:46 ` [PATCH 04/16] mm: numa: Do not migrate or account for hinting faults on the zero page Mel Gorman
2013-07-11 11:21 ` Peter Zijlstra
2013-07-11 12:42 ` Mel Gorman
2013-07-11 9:46 ` [PATCH 05/16] sched: Select a preferred node with the most numa hinting faults Mel Gorman
2013-07-11 11:23 ` Peter Zijlstra
2013-07-11 12:53 ` Mel Gorman
2013-07-11 9:46 ` [PATCH 06/16] sched: Update NUMA hinting faults once per scan Mel Gorman
2013-07-11 9:46 ` [PATCH 07/16] sched: Favour moving tasks towards the preferred node Mel Gorman
2013-07-11 9:46 ` [PATCH 08/16] sched: Reschedule task on preferred NUMA node once selected Mel Gorman
2013-07-11 12:30 ` Peter Zijlstra
2013-07-11 13:03 ` Mel Gorman [this message]
2013-07-11 13:11 ` Peter Zijlstra
2013-07-11 14:09 ` Mel Gorman
2013-07-12 10:14 ` Peter Zijlstra
2013-07-12 10:28 ` Mel Gorman
2013-07-11 9:46 ` [PATCH 09/16] sched: Add infrastructure for split shared/private accounting of NUMA hinting faults Mel Gorman
2013-07-11 9:46 ` [PATCH 10/16] sched: Increase NUMA PTE scanning when a new preferred node is selected Mel Gorman
2013-07-11 9:46 ` [PATCH 11/16] sched: Check current->mm before allocating NUMA faults Mel Gorman
2013-07-11 9:46 ` [PATCH 12/16] sched: Set the scan rate proportional to the size of the task being scanned Mel Gorman
2013-07-11 9:46 ` [PATCH 13/16] mm: numa: Scan pages with elevated page_mapcount Mel Gorman
2013-07-11 9:46 ` [PATCH 14/16] sched: Remove check that skips small VMAs Mel Gorman
2013-07-11 9:46 ` [PATCH 15/16] sched: Set preferred NUMA node based on number of private faults Mel Gorman
2013-07-11 9:47 ` [PATCH 16/16] sched: Select least loaded CPU on preferred NUMA node Mel Gorman
2013-07-11 12:39 ` Peter Zijlstra
2013-07-11 13:24 ` Mel Gorman
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