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From: Vincent Guittot <vincent.guittot@linaro.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Phil Auld <pauld@redhat.com>, Hillf Danton <hdanton@sina.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v3
Date: Mon, 17 Feb 2020 17:15:32 +0100	[thread overview]
Message-ID: <CAKfTPtDEFvYv3oOAzDHZE5BLE0AByvvHB+67yL=SfAQgEotbGw@mail.gmail.com> (raw)
In-Reply-To: <20200217151412.GK3466@techsingularity.net>

On Mon, 17 Feb 2020 at 16:14, Mel Gorman <mgorman@techsingularity.net> wrote:
>
> On Mon, Feb 17, 2020 at 02:49:11PM +0100, Vincent Guittot wrote:
> > On Mon, 17 Feb 2020 at 11:44, Mel Gorman <mgorman@techsingularity.net> wrote:
> > >
> > > Changelog since V2:
> > > o Rebase on top of Vincent's series again
> > > o Fix a missed rcu_read_unlock
> > > o Reduce overhead of tracepoint
> > >
> > > Changelog since V1:
> > > o Rebase on top of Vincent's series and rework
> > >
> > > Note: The baseline for this series is tip/sched/core as of February
> > >         12th rebased on top of v5.6-rc1. The series includes patches from
> > >         Vincent as I needed to add a fix and build on top of it. Vincent's
> > >         series on its own introduces performance regressions for *some*
> > >         but not *all* machines so it's easily missed. This series overall
> > >         is close to performance-neutral with some gains depending on the
> > >         machine. However, the end result does less work on NUMA balancing
> > >         and the fact that both the NUMA balancer and load balancer uses
> > >         similar logic makes it much easier to understand.
> > >
> > > The NUMA balancer makes placement decisions on tasks that partially
> > > take the load balancer into account and vice versa but there are
> > > inconsistencies. This can result in placement decisions that override
> > > each other leading to unnecessary migrations -- both task placement
> > > and page placement. This series reconciles many of the decisions --
> > > partially Vincent's work with some fixes and optimisations on top to
> > > merge our two series.
> > >
> > > The first patch is unrelated. It's picked up by tip but was not present in
> > > the tree at the time of the fork. I'm including it here because I tested
> > > with it.
> > >
> > > The second and third patches are tracing only and was needed to get
> > > sensible data out of ftrace with respect to task placement for NUMA
> > > balancing. The NUMA balancer is *far* easier to analyse with the
> > > patches and informed how the series should be developed.
> > >
> > > Patches 4-5 are Vincent's and use very similar code patterns and logic
> > > between NUMA and load balancer. Patch 6 is a fix to Vincent's work that
> > > is necessary to avoid serious imbalances being introduced by the NUMA
> >
> > Yes the test added in load_too_imbalanced() by patch 5 doesn't seem to
> > be a good choice.
>
> But it *did* make sense intuitively!

Yes. In fact, one difference compared to your fix is that
load_too_imbalance() is also called by task_numa_compare() whereas
node_type only is only tested in task_numa_find_cpu() in your patch

>
> > I haven't remove it as it was done by your patch 6 but it might worth
> > removing it directly if a new version is needed
> >
>
> They could be folded together or part folded together but I did not see
> much value in that. I felt that keeping them seperate both preserved the
> development history and acted as a historical reference on why using a
> spare CPU can be hazardous. I do not believe it is a bisection hazard
> as performance is roughly equivalent before and after the series (so
> far at least). LKP might trip up on it and if so, we'll simply ask for
> confirmation that patch 6 fixes it.

that's fine for me

>
> --
> Mel Gorman
> SUSE Labs

  reply	other threads:[~2020-02-17 16:15 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-17 10:43 [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v3 Mel Gorman
2020-02-17 10:43 ` [PATCH 01/13] sched/fair: Allow a per-CPU kthread waking a task to stack on the same CPU, to fix XFS performance regression Mel Gorman
2020-02-17 10:43 ` [PATCH 02/13] sched/numa: Trace when no candidate CPU was found on the preferred node Mel Gorman
2020-02-17 10:43 ` [PATCH 03/13] sched/numa: Distinguish between the different task_numa_migrate failure cases Mel Gorman
2020-02-17 10:43 ` [PATCH 04/13] sched/fair: Reorder enqueue/dequeue_task_fair path Mel Gorman
2020-02-17 10:43 ` [PATCH 05/13] sched/numa: Replace runnable_load_avg by load_avg Mel Gorman
2020-02-17 10:43 ` [PATCH 06/13] sched/numa: Use similar logic to the load balancer for moving between domains with spare capacity Mel Gorman
2020-02-17 10:43 ` [PATCH 07/13] sched/pelt: Remove unused runnable load average Mel Gorman
2020-02-17 10:43 ` [PATCH 08/13] sched/pelt: Add a new runnable average signal Mel Gorman
2020-02-17 10:43 ` [PATCH 09/13] sched/fair: Take into account runnable_avg to classify group Mel Gorman
2020-02-17 10:43 ` [PATCH 10/13] sched/numa: Prefer using an idle cpu as a migration target instead of comparing tasks Mel Gorman
2020-02-17 10:44 ` [PATCH 11/13] sched/numa: Find an alternative idle CPU if the CPU is part of an active NUMA balance Mel Gorman
2020-02-17 10:44 ` [PATCH 12/13] sched/numa: Bias swapping tasks based on their preferred node Mel Gorman
2020-02-17 10:44 ` [PATCH 13/13] sched/numa: Stop an exhastive search if a reasonable swap candidate or idle CPU is found Mel Gorman
2020-02-17 13:49 ` [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v3 Vincent Guittot
2020-02-17 14:52   ` Peter Zijlstra
2020-02-17 15:31     ` Mel Gorman
2020-02-17 15:14   ` Mel Gorman
2020-02-17 16:15     ` Vincent Guittot [this message]
     [not found] ` <20200217132019.6684-1-hdanton@sina.com>
2020-02-17 15:06   ` [PATCH 06/13] sched/numa: Use similar logic to the load balancer for moving between domains with spare capacity Mel Gorman
     [not found]   ` <20200218033244.6860-1-hdanton@sina.com>
2020-02-18  8:47     ` Mel Gorman
     [not found]     ` <20200218095915.844-1-hdanton@sina.com>
2020-02-18 10:53       ` Mel Gorman

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