From: Mel Gorman <mgorman@techsingularity.net>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Juri Lelli <juri.lelli@redhat.com>
Subject: Re: [PATCH 2/3] sched/numa: Allow a floating imbalance between NUMA nodes
Date: Tue, 17 Nov 2020 14:44:38 +0000 [thread overview]
Message-ID: <20201117144438.GA3371@techsingularity.net> (raw)
In-Reply-To: <CAKfTPtBj1nJhQrsAoH0mBrc9Md+_icNJuWx7P=yQbqM2fYCAwg@mail.gmail.com>
On Tue, Nov 17, 2020 at 03:24:56PM +0100, Vincent Guittot wrote:
> On Tue, 17 Nov 2020 at 14:42, Mel Gorman <mgorman@techsingularity.net> wrote:
> >
> > Currently, an imbalance is only allowed when a destination node
> > is almost completely idle. This solved one basic class of problems
> > and was the cautious approach.
> >
> > This patch revisits the possibility that NUMA nodes can be imbalanced
> > until 25% of the CPUs are occupied. The reasoning behind 25% is somewhat
> > superficial -- it's half the cores when HT is enabled. At higher
> > utilisations, balancing should continue as normal and keep things even
> > until scheduler domains are fully busy or over utilised.
>
> This reminds me previous discussions on the same topic: how much
> imbalance is allowed that will not screw up the bandwidth of the node
> I'm worried that there is no topology insight in the decision like
> hyperthreading, or number of cpus in the LLC
>
We still don't have a good answer for that. It could be a tunable I guess
but it would be horrible to tune properly.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2020-11-17 14:44 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-17 13:42 [RFC PATCH 0/3] Revisit NUMA imbalance tolerance and fork balancing Mel Gorman
2020-11-17 13:42 ` [PATCH 1/3] sched/numa: Rename nr_running and break out the magic number Mel Gorman
2020-11-17 13:42 ` [PATCH 2/3] sched/numa: Allow a floating imbalance between NUMA nodes Mel Gorman
2020-11-17 14:16 ` Peter Zijlstra
2020-11-17 14:43 ` Mel Gorman
2020-11-17 14:24 ` Vincent Guittot
2020-11-17 14:44 ` Mel Gorman [this message]
2020-11-17 13:42 ` [PATCH 3/3] sched/numa: Limit the amount of imbalance that can exist at fork time Mel Gorman
2020-11-17 14:18 ` Peter Zijlstra
2020-11-17 14:31 ` Vincent Guittot
2020-11-17 15:17 ` Mel Gorman
2020-11-17 15:53 ` Vincent Guittot
2020-11-17 17:28 ` Mel Gorman
2020-11-18 16:06 ` Vincent Guittot
2020-11-18 16:50 ` Mel Gorman
2020-11-22 15:04 ` [sched/numa] e7f28850ea: unixbench.score 1.5% improvement kernel test robot
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