From: Mel Gorman <mgorman@techsingularity.net>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Mike Galbraith <efault@gmx.de>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Aubrey Li <aubrey.li@linux.intel.com>,
Barry Song <song.bao.hua@hisilicon.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] sched/fair: Scale wakeup granularity relative to nr_running
Date: Wed, 22 Sep 2021 19:57:24 +0100 [thread overview]
Message-ID: <20210922185724.GD3959@techsingularity.net> (raw)
In-Reply-To: <CAKfTPtDc39fCLbQqA2BhC6dsb+MyYYMdk9HUvrU0fRqULuQB-g@mail.gmail.com>
On Wed, Sep 22, 2021 at 08:22:43PM +0200, Vincent Guittot wrote:
> > > > > In
> > > > > your case, you want hackbench threads to not preempt each others
> > > > > because they tries to use same resources so it's probably better to
> > > > > let the current one to move forward but that's not a universal policy.
> > > > >
> > > >
> > > > No, but have you a better suggestion? hackbench might be stupid but it's
> > > > an example of where a workload can excessively preempt itself. While
> > > > overloading an entire machine is stupid, it could also potentially occurs
> > > > for applications running within a constrained cpumask.
> > >
> > > But this is property that is specific to each application. Some can
> > > have a lot of running threads but few wakes up which have to preempt
> > > current threads quickly but others just want the opposite
> > > So because it is a application specific property we should define it
> > > this way instead of trying to guess
> >
> > I'm not seeing an alternative suggestion that could be turned into
> > an implementation. The current value for sched_wakeup_granularity
> > was set 12 years ago was exposed for tuning which is no longer
> > the case. The intent was to allow some dynamic adjustment between
> > sysctl_sched_wakeup_granularity and sysctl_sched_latency to reduce
> > over-scheduling in the worst case without disabling preemption entirely
> > (which the first version did).
> >
> > Should we just ignore this problem and hope it goes away or just let
> > people keep poking silly values into debugfs via tuned?
>
> We should certainly not add a bandaid because people will continue to
> poke silly value at the end. And increasing
> sysctl_sched_wakeup_granularity based on the number of running threads
> is not the right solution. According to the description of your
> problem that the current task doesn't get enough time to move forward,
> sysctl_sched_min_granularity should be part of the solution. Something
> like below will ensure that current got a chance to move forward
>
That's a very interesting idea! I've queued it up for further testing
and as a comparison to the bandaid.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2021-09-22 18:57 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-20 14:26 [PATCH 0/2] " Mel Gorman
2021-09-20 14:26 ` [PATCH 1/2] sched/fair: Remove redundant lookup of rq in check_preempt_wakeup Mel Gorman
2021-09-21 7:21 ` Vincent Guittot
2021-09-21 7:53 ` Mel Gorman
2021-09-21 8:12 ` Vincent Guittot
2021-09-21 8:21 ` Peter Zijlstra
2021-09-21 10:03 ` Mel Gorman
2021-09-20 14:26 ` [PATCH 2/2] sched/fair: Scale wakeup granularity relative to nr_running Mel Gorman
2021-09-21 3:52 ` Mike Galbraith
2021-09-21 5:50 ` Mike Galbraith
2021-09-21 7:04 ` Mike Galbraith
2021-09-21 10:36 ` Mel Gorman
2021-09-21 12:32 ` Mike Galbraith
2021-09-21 14:03 ` Mel Gorman
2021-10-05 9:24 ` Peter Zijlstra
2021-09-22 5:22 ` Mike Galbraith
2021-09-22 13:20 ` Mel Gorman
2021-09-22 14:04 ` Mike Galbraith
2021-09-22 14:15 ` Vincent Guittot
2021-09-22 15:04 ` Mel Gorman
2021-09-22 16:00 ` Vincent Guittot
2021-09-22 17:38 ` Mel Gorman
2021-09-22 18:22 ` Vincent Guittot
2021-09-22 18:57 ` Mel Gorman [this message]
2021-09-23 1:47 ` Mike Galbraith
2021-09-23 8:40 ` Vincent Guittot
2021-09-23 9:21 ` Mike Galbraith
2021-09-23 12:41 ` Vincent Guittot
2021-09-23 13:14 ` Mike Galbraith
2021-09-27 11:17 ` Mel Gorman
2021-09-27 14:17 ` Mike Galbraith
2021-10-04 8:05 ` Mel Gorman
2021-10-04 16:37 ` Vincent Guittot
2021-10-05 7:41 ` Mel Gorman
2021-09-27 14:19 ` Vincent Guittot
2021-09-27 15:02 ` Mel Gorman
2021-09-23 12:24 ` Phil Auld
2021-10-05 10:36 ` Peter Zijlstra
2021-10-05 14:12 ` Phil Auld
2021-10-05 14:32 ` Peter Zijlstra
2021-10-05 10:28 ` Peter Zijlstra
2021-10-05 10:23 ` Peter Zijlstra
2021-10-05 9:41 ` Peter Zijlstra
2021-09-22 15:05 ` Vincent Guittot
2021-10-05 9:32 ` Peter Zijlstra
2021-10-03 3:07 ` wakeup_affine_weight() is b0rked - was " Mike Galbraith
2021-10-03 7:34 ` Barry Song
2021-10-03 14:52 ` Mike Galbraith
2021-10-03 21:06 ` Barry Song
2021-10-04 1:49 ` Mike Galbraith
2021-10-04 4:34 ` Mike Galbraith
2021-10-04 9:06 ` Mike Galbraith
2021-10-05 7:47 ` Mel Gorman
2021-10-05 8:42 ` Mike Galbraith
2021-10-05 9:31 ` Mel Gorman
2021-10-06 6:46 ` Mike Galbraith
2021-10-08 5:06 ` Mike Galbraith
2021-09-21 8:03 ` Vincent Guittot
2021-09-21 10:45 ` Mel Gorman
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