From: Peter Zijlstra <peterz@infradead.org>
To: Steven Sistare <steven.sistare@oracle.com>
Cc: mingo@redhat.com, subhra.mazumdar@oracle.com,
dhaval.giani@oracle.com, daniel.m.jordan@oracle.com,
pavel.tatashin@microsoft.com, matt@codeblueprint.co.uk,
umgwanakikbuti@gmail.com, riel@redhat.com, jbacik@fb.com,
juri.lelli@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/10] steal tasks to improve CPU utilization
Date: Tue, 23 Oct 2018 00:09:35 +0200 [thread overview]
Message-ID: <20181022220935.GD3109@worktop.c.hoisthospitality.com> (raw)
In-Reply-To: <8e38ce84-ec1a-aef7-4784-462ef754f62a@oracle.com>
On Mon, Oct 22, 2018 at 03:07:10PM -0400, Steven Sistare wrote:
> On 10/22/2018 1:04 PM, Peter Zijlstra wrote:
> > On Mon, Oct 22, 2018 at 07:59:31AM -0700, Steve Sistare wrote:
> >> When a CPU has no more CFS tasks to run, and idle_balance() fails to
> >> find a task, then attempt to steal a task from an overloaded CPU in the
> >> same LLC. Maintain and use a bitmap of overloaded CPUs to efficiently
> >> identify candidates. To minimize search time, steal the first migratable
> >> task that is found when the bitmap is traversed. For fairness, search
> >> for migratable tasks on an overloaded CPU in order of next to run.
> >>
> >> This simple stealing yields a higher CPU utilization than idle_balance()
> >> alone, because the search is cheap, so it may be called every time the CPU
> >> is about to go idle. idle_balance() does more work because it searches
> >> widely for the busiest queue, so to limit its CPU consumption, it declines
> >> to search if the system is too busy. Simple stealing does not offload the
> >> globally busiest queue, but it is much better than running nothing at all.
> >
> > Why I don't dislike the idea; I feel it is unfortunate to have two
> > different mechanisms to do effectively the same thing.
> >
> > Can't we improve idle_balance() instead of building this parallel
> > functionality?
>
> We could delete idle_balance() and use stealing exclusively for handling
> new idle. For each sd level, stealing would look for an overloaded CPU
> in the overloaded bitmap(s) that overlap that level. I played with that
> a little but it is not ready for prime time, and I did not want to hold
> the patch series for it. Also, I would like folks to get some production
> experience with stealing on a variety of architectures before considering
> a radical step like replacing idle_balance().
Fair enough. And yes, it might make sense to fully replace the current
newidle balance with something along these lines.
> We could remove the core and socket levels from idle_balance() and let
> stealing handle those levels. I think that makes sense after stealing
> performance is validated on more architectures, but we would still have
> two different mechanisms.
Yes, this would be a fairly simple change and make sense until we have a
full replacement.
> We could merge the stealing code into the idle_balance() code to get a
> union of the two, but IMO that would be less readable.
Agreed; I don't think that'll be pretty.
next prev parent reply other threads:[~2018-10-22 22:17 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-22 14:59 [PATCH 00/10] steal tasks to improve CPU utilization Steve Sistare
2018-10-22 14:59 ` [PATCH 01/10] sched: Provide sparsemask, a reduced contention bitmap Steve Sistare
2018-10-22 14:59 ` [PATCH 02/10] sched/topology: Provide hooks to allocate data shared per LLC Steve Sistare
2018-10-22 14:59 ` [PATCH 03/10] sched/topology: Provide cfs_overload_cpus bitmap Steve Sistare
2018-10-22 14:59 ` [PATCH 04/10] sched/fair: Dynamically update cfs_overload_cpus Steve Sistare
2018-10-22 16:56 ` Peter Zijlstra
2018-10-22 18:43 ` Steven Sistare
2018-10-22 14:59 ` [PATCH 05/10] sched/fair: Hoist idle_stamp up from idle_balance Steve Sistare
2018-10-25 13:47 ` Valentin Schneider
2018-10-25 14:04 ` Steven Sistare
2018-10-22 14:59 ` [PATCH 06/10] sched/fair: Generalize the detach_task interface Steve Sistare
2018-10-22 14:59 ` [PATCH 07/10] sched/fair: Provide can_migrate_task_llc Steve Sistare
2018-10-26 18:04 ` Valentin Schneider
2018-10-26 18:28 ` Steven Sistare
2018-10-29 19:34 ` Valentin Schneider
2018-10-31 15:43 ` Steven Sistare
2018-10-31 18:48 ` Valentin Schneider
2018-10-31 19:14 ` Peter Zijlstra
2018-11-01 11:16 ` Valentin Schneider
2018-10-22 14:59 ` [PATCH 08/10] sched/fair: Steal work from an overloaded CPU when CPU goes idle Steve Sistare
2018-10-25 13:48 ` Valentin Schneider
2018-10-25 14:07 ` Steven Sistare
2018-10-22 14:59 ` [PATCH 09/10] sched/fair: disable stealing if too many NUMA nodes Steve Sistare
2018-10-22 17:06 ` Peter Zijlstra
2018-10-22 18:47 ` Steven Sistare
2018-10-22 19:21 ` Steven Sistare
2018-10-22 22:05 ` Peter Zijlstra
2018-10-23 13:18 ` Steven Sistare
2018-10-22 14:59 ` [PATCH 10/10] sched/fair: Provide idle search schedstats Steve Sistare
2018-10-22 17:04 ` [PATCH 00/10] steal tasks to improve CPU utilization Peter Zijlstra
2018-10-22 19:07 ` Steven Sistare
2018-10-22 22:09 ` Peter Zijlstra [this message]
2018-10-24 15:34 ` Valentin Schneider
2018-10-24 19:27 ` Steven Sistare
2018-10-25 11:31 ` Valentin Schneider
2018-10-25 12:21 ` Steven Sistare
2018-10-25 7:50 ` Vincent Guittot
2018-10-25 11:28 ` Steven Sistare
2018-10-25 12:43 ` Vincent Guittot
2018-10-25 14:19 ` Steven Sistare
2018-10-31 19:35 ` Steven Sistare
2018-11-01 11:56 ` Steven Sistare
2018-11-02 23:39 ` Subhra Mazumdar
2018-11-05 20:08 ` Steven Sistare
2019-01-04 13:37 ` Shijith Thotton
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