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From: Valentin Schneider <valentin.schneider@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Sistare <steven.sistare@oracle.com>,
	mingo@redhat.com, subhra.mazumdar@oracle.com,
	dhaval.giani@oracle.com, rohit.k.jain@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 07/10] sched/fair: Provide can_migrate_task_llc
Date: Thu, 1 Nov 2018 11:16:37 +0000	[thread overview]
Message-ID: <10491016-9eec-846f-9632-f6de965508b6@arm.com> (raw)
In-Reply-To: <20181031191459.GA3141@hirez.programming.kicks-ass.net>

On 31/10/2018 19:14, Peter Zijlstra wrote:
> On Mon, Oct 29, 2018 at 07:34:50PM +0000, Valentin Schneider wrote:
>> On a sidenote, I find it a bit odd that the exec_start threshold depends on
>> sysctl_sched_migration_cost, which to me is more about idle_balance() cost
>> than "how long does it take for a previously run task to go cache cold".
> 
> A long long (think 2.6.20 long ago) there was code that did boot-time
> measurement of the various cache topology costs and that threshold was
> related to that.
> 
> That code got killed because of boot to boot variance and dubious
> benefits.
> 
> The migration cost is what it was replaced with as a single measure.
> 
> migration cost was then later abused in the newidle balance because it
> was over eager.


Thanks! I tried following the blame rabbit hole but got a bit lost along
the way.

> Ideally we'd get rid of it there, because we've now got
> that much more elaborate accounting, but Rohit tried and found some
> regression because of that.
> 
> Maybe we should remove it from newidle anyway.
> 

Well, if we ditch idle_balance() in favor of stealing, that would "solve"
it...

  reply	other threads:[~2018-11-01 11:16 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 [this message]
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
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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