From: Mel Gorman <mgorman@suse.de>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
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 16/18] sched: Avoid overloading CPUs on a preferred NUMA node
Date: Thu, 1 Aug 2013 16:42:28 +0100 [thread overview]
Message-ID: <20130801154228.GE2296@suse.de> (raw)
In-Reply-To: <20130801071013.GG4880@linux.vnet.ibm.com>
On Thu, Aug 01, 2013 at 12:40:13PM +0530, Srikar Dronamraju wrote:
> > +static int task_numa_find_cpu(struct task_struct *p, int nid)
> > +{
> > + int node_cpu = cpumask_first(cpumask_of_node(nid));
> > + int cpu, src_cpu = task_cpu(p), dst_cpu = src_cpu;
> > + unsigned long src_load, dst_load;
> > + unsigned long min_load = ULONG_MAX;
> > + struct task_group *tg = task_group(p);
> > + s64 src_eff_load, dst_eff_load;
> > + struct sched_domain *sd;
> > + unsigned long weight;
> > + bool balanced;
> > + int imbalance_pct, idx = -1;
> >
> > + /* No harm being optimistic */
> > + if (idle_cpu(node_cpu))
> > + return node_cpu;
>
> Cant this lead to lot of imbalance across nodes? Wont this lead to lot
> of ping-pong of tasks between different nodes resulting in performance
> hit?
Ideally it wouldn't because if we are trying to migrate the task to here in
the first place then it must have been scheduled there for long enough to
accumulate those faults. Now, there might be a ping-pong effect because a
tasks gets moved off by the load balancer because the CPUs are overloaded and
now we're trying to move it back. If we can detect that this is happening
then one way of dealing with it would be to clear p->numa_faults[] when
a task is moved off a node due to compute overload.
> Lets say the system is not fully loaded, something like a numa01
> but with far lesser number of threads probably nr_cpus/2 or nr_cpus/4,
> then all threads will try to move to single node as we can keep seeing
> idle threads. No? Wont it lead all load moving to one node and load
> balancer spreading it out...
>
I cannot be 100% certain. I'm not strong enough on the scheduler yet and
the compute overloading handling is currently too weak.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2013-08-01 15:42 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-15 15:20 [PATCH 0/18] Basic scheduler support for automatic NUMA balancing V5 Mel Gorman
2013-07-15 15:20 ` [PATCH 01/18] mm: numa: Document automatic NUMA balancing sysctls Mel Gorman
2013-07-15 15:20 ` [PATCH 02/18] sched: Track NUMA hinting faults on per-node basis Mel Gorman
2013-07-17 10:50 ` Peter Zijlstra
2013-07-31 7:54 ` Mel Gorman
2013-07-29 10:10 ` Peter Zijlstra
2013-07-31 7:54 ` Mel Gorman
2013-07-15 15:20 ` [PATCH 03/18] mm: numa: Account for THP numa hinting faults on the correct node Mel Gorman
2013-07-17 0:33 ` Hillf Danton
2013-07-15 15:20 ` [PATCH 04/18] mm: numa: Do not migrate or account for hinting faults on the zero page Mel Gorman
2013-07-17 11:00 ` Peter Zijlstra
2013-07-31 8:11 ` Mel Gorman
2013-07-15 15:20 ` [PATCH 05/18] sched: Select a preferred node with the most numa hinting faults Mel Gorman
2013-07-15 15:20 ` [PATCH 06/18] sched: Update NUMA hinting faults once per scan Mel Gorman
2013-07-15 15:20 ` [PATCH 07/18] sched: Favour moving tasks towards the preferred node Mel Gorman
2013-07-25 10:40 ` [PATCH] sched, numa: migrates_degrades_locality() Peter Zijlstra
2013-07-31 8:44 ` Mel Gorman
2013-07-31 8:50 ` Peter Zijlstra
2013-07-15 15:20 ` [PATCH 08/18] sched: Reschedule task on preferred NUMA node once selected Mel Gorman
2013-07-17 1:31 ` Hillf Danton
2013-07-31 9:07 ` Mel Gorman
2013-07-31 9:38 ` Srikar Dronamraju
2013-08-01 4:47 ` Srikar Dronamraju
2013-08-01 15:38 ` Mel Gorman
2013-07-15 15:20 ` [PATCH 09/18] sched: Add infrastructure for split shared/private accounting of NUMA hinting faults Mel Gorman
2013-07-17 2:17 ` Hillf Danton
2013-07-31 9:08 ` Mel Gorman
2013-07-15 15:20 ` [PATCH 10/18] sched: Increase NUMA PTE scanning when a new preferred node is selected Mel Gorman
2013-07-15 15:20 ` [PATCH 11/18] sched: Check current->mm before allocating NUMA faults Mel Gorman
2013-07-15 15:20 ` [PATCH 12/18] sched: Set the scan rate proportional to the size of the task being scanned Mel Gorman
2013-07-15 15:20 ` [PATCH 13/18] mm: numa: Scan pages with elevated page_mapcount Mel Gorman
2013-07-17 5:22 ` Sam Ben
2013-07-31 9:13 ` Mel Gorman
2013-07-15 15:20 ` [PATCH 14/18] sched: Remove check that skips small VMAs Mel Gorman
2013-07-15 15:20 ` [PATCH 15/18] sched: Set preferred NUMA node based on number of private faults Mel Gorman
2013-07-18 1:53 ` [PATCH 15/18] fix compilation with !CONFIG_NUMA_BALANCING Rik van Riel
2013-07-31 9:19 ` Mel Gorman
2013-07-26 11:20 ` [PATCH 15/18] sched: Set preferred NUMA node based on number of private faults Peter Zijlstra
2013-07-31 9:29 ` Mel Gorman
2013-07-31 9:34 ` Peter Zijlstra
2013-07-31 10:10 ` Mel Gorman
2013-07-15 15:20 ` [PATCH 16/18] sched: Avoid overloading CPUs on a preferred NUMA node Mel Gorman
2013-07-15 20:03 ` Peter Zijlstra
2013-07-16 8:23 ` Mel Gorman
2013-07-16 10:35 ` Peter Zijlstra
2013-07-16 15:55 ` Hillf Danton
2013-07-16 16:01 ` Mel Gorman
2013-07-17 10:54 ` Peter Zijlstra
2013-07-31 9:49 ` Mel Gorman
2013-08-01 7:10 ` Srikar Dronamraju
2013-08-01 15:42 ` Mel Gorman [this message]
2013-07-15 15:20 ` [PATCH 17/18] sched: Retry migration of tasks to CPU on a preferred node Mel Gorman
2013-07-25 10:33 ` Peter Zijlstra
2013-07-31 10:03 ` Mel Gorman
2013-07-31 10:05 ` Peter Zijlstra
2013-07-31 10:07 ` Mel Gorman
2013-07-25 10:35 ` Peter Zijlstra
2013-08-01 5:13 ` Srikar Dronamraju
2013-08-01 15:46 ` Mel Gorman
2013-07-15 15:20 ` [PATCH 18/18] sched: Swap tasks when reschuling if a CPU on a target node is imbalanced Mel Gorman
2013-07-15 20:11 ` Peter Zijlstra
2013-07-16 9:41 ` Mel Gorman
2013-08-01 4:59 ` Srikar Dronamraju
2013-08-01 15:48 ` Mel Gorman
2013-07-15 20:14 ` [PATCH 0/18] Basic scheduler support for automatic NUMA balancing V5 Peter Zijlstra
2013-07-16 15:10 ` Srikar Dronamraju
2013-07-25 10:36 ` Peter Zijlstra
2013-07-31 10:30 ` Mel Gorman
2013-07-31 10:48 ` Peter Zijlstra
2013-07-31 11:57 ` Mel Gorman
2013-07-31 15:30 ` Peter Zijlstra
2013-07-31 16:11 ` Mel Gorman
2013-07-31 16:39 ` Peter Zijlstra
2013-08-01 15:51 ` Mel Gorman
2013-07-25 10:38 ` [PATCH] mm, numa: Sanitize task_numa_fault() callsites Peter Zijlstra
2013-07-31 11:25 ` Mel Gorman
2013-07-25 10:41 ` [PATCH] sched, numa: Improve scanner Peter Zijlstra
2013-07-25 10:46 ` [PATCH] mm, sched, numa: Create a per-task MPOL_INTERLEAVE policy Peter Zijlstra
2013-07-26 9:55 ` Peter Zijlstra
2013-08-26 16:10 ` Peter Zijlstra
2013-08-26 16:14 ` Peter Zijlstra
2013-07-30 11:24 ` [PATCH] mm, numa: Change page last {nid,pid} into {cpu,pid} Peter Zijlstra
2013-08-01 22:33 ` Rik van Riel
2013-07-30 11:38 ` [PATCH] sched, numa: Use {cpu, pid} to create task groups for shared faults Peter Zijlstra
2013-07-31 15:07 ` Peter Zijlstra
2013-07-31 15:38 ` Peter Zijlstra
2013-07-31 15:45 ` Don Morris
2013-07-31 16:05 ` Peter Zijlstra
2013-08-02 16:47 ` [PATCH -v3] " Peter Zijlstra
2013-08-02 16:50 ` [PATCH] mm, numa: Do not group on RO pages Peter Zijlstra
2013-08-02 19:56 ` Peter Zijlstra
2013-08-05 19:36 ` [PATCH] numa,sched: use group fault statistics in numa placement Rik van Riel
2013-08-09 13:55 ` Don Morris
2013-08-28 16:41 ` [PATCH -v3] sched, numa: Use {cpu, pid} to create task groups for shared faults Peter Zijlstra
2013-08-28 17:10 ` Rik van Riel
2013-08-01 6:23 ` [PATCH,RFC] numa,sched: use group fault statistics in numa placement Rik van Riel
2013-08-01 10:37 ` Peter Zijlstra
2013-08-01 16:35 ` Rik van Riel
2013-08-01 22:36 ` [RFC PATCH -v2] " Rik van Riel
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