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From: Peter Zijlstra <peterz@infradead.org>
To: Mike Galbraith <mgalbraith@suse.de>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@elte.hu>, Paul Turner <pjt@google.com>
Subject: Re: [patch 4/7] sched: convert rq->avg_idle to rq->avg_event
Date: Wed, 23 Nov 2011 13:27:26 +0100	[thread overview]
Message-ID: <1322051246.14799.58.camel@twins> (raw)
In-Reply-To: <1322050165.7041.5.camel@marge.simson.net>

On Wed, 2011-11-23 at 13:09 +0100, Mike Galbraith wrote:
> On Wed, 2011-11-23 at 12:55 +0100, Peter Zijlstra wrote:
> > On Tue, 2011-11-22 at 15:22 +0100, Mike Galbraith wrote:
> > > We update rq->clock only at points of interest to the scheduler.
> > > Using this distance has the same effect as measuring idle time
> > > for idle_balance() throttling, and allows other uses as well. 
> > 
> > I'm not sure I follow, suppose we're happily context switching away, how
> > is the avg distance between context switches related to idle time?
> 
> Average idle time can't be larger.

True :-)

But it can be _much MUCH_ smaller. So the value is a fair upper limit on
the idle time, but has no relation to the actual idle duration.

Now this value seems to be used in 5 to throttle select_idle_sibling(),
which is again something unrelated to actual idle duration, but also
unrelated to the avg update_rq_clock() interval.

In patch 6 we use this value to guestimate if we should enter nohz,
since its a wild over estimation of the actual idle duration it'll be
less effective and might not hard much.

Also, patch 6's use of sched_migration_cost to reflect the nohz
enter/exit cost is somewhat iffy, but that's another issue.


Now I'm not saying this all isn't worth it, just saying my brain is
having difficulty seeing how it all makes sense :-)

Anyway, I picked up 1,2,3,7 and will give the missing patches another
stare a bit later.

  reply	other threads:[~2011-11-23 12:27 UTC|newest]

Thread overview: 79+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-11-15  9:46 sched: Avoid SMT siblings in select_idle_sibling() if possible Peter Zijlstra
2011-11-16  1:14 ` Suresh Siddha
2011-11-16  9:24   ` Mike Galbraith
2011-11-16 18:37     ` Suresh Siddha
2011-11-17  1:59       ` Mike Galbraith
2011-11-17 15:38         ` Mike Galbraith
2011-11-17 15:56           ` Peter Zijlstra
2011-11-17 16:38             ` Mike Galbraith
2011-11-17 17:36               ` Suresh Siddha
2011-11-18 15:14                 ` Mike Galbraith
2011-11-18 15:17                   ` [patch 1/6] sched: use rt.nr_cpus_allowed to recover select_task_rq() cycles Mike Galbraith
2011-11-18 15:35                     ` Peter Zijlstra
2011-11-18 17:34                       ` Mike Galbraith
2011-11-22 14:17                       ` Mike Galbraith
2011-11-22 14:18                         ` [patch 1/7] " Mike Galbraith
2011-12-06  9:50                           ` [tip:sched/core] sched: Use " tip-bot for Mike Galbraith
2011-11-22 14:20                         ` [patch 2/7] sched: save some hrtick_start_fair cycles Mike Galbraith
2011-12-06 20:20                           ` [tip:sched/core] sched: Save " tip-bot for Mike Galbraith
2011-11-22 14:21                         ` [patch 3/7] sched: set skip_clock_update in yield_task_fair() Mike Galbraith
2011-11-23 11:53                           ` Peter Zijlstra
2011-11-23 12:06                             ` Mike Galbraith
2011-11-23 14:48                           ` Peter Zijlstra
2011-11-24  3:50                             ` Mike Galbraith
2011-11-24 10:12                               ` Peter Zijlstra
2011-11-25  6:39                                 ` Mike Galbraith
2011-12-06  9:51                           ` [tip:sched/core] sched: Set " tip-bot for Mike Galbraith
2011-11-22 14:22                         ` [patch 4/7] sched: convert rq->avg_idle to rq->avg_event Mike Galbraith
2011-11-23 11:55                           ` Peter Zijlstra
2011-11-23 12:09                             ` Mike Galbraith
2011-11-23 12:27                               ` Peter Zijlstra [this message]
2011-11-23 12:57                                 ` Mike Galbraith
2011-11-23 14:21                                   ` Mike Galbraith
2011-11-22 14:23                         ` [patch 5/7] sched: ratelimit select_idle_sibling()for sync wakeups Mike Galbraith
2011-11-22 14:24                         ` [patch 6/7] sched: use rq->avg_event to resurrect nohz ratelimiting Mike Galbraith
2011-11-23 11:57                           ` Peter Zijlstra
2011-11-23 12:35                           ` Mike Galbraith
2011-11-22 14:26                         ` [patch 7/7] sched: only use TTWU_QUEUE when waker/wakee CPUs do not share top level cache Mike Galbraith
2011-11-23 12:08                           ` Peter Zijlstra
2011-11-18 15:39                     ` [patch 1/6] sched: use rt.nr_cpus_allowed to recover select_task_rq() cycles Hillf Danton
2011-11-18 15:18                   ` [patch 2/6] sched: convert rq->avg_idle to rq->avg_event Mike Galbraith
2011-11-18 15:19                   ` [patch 3/6] sched: use rq->avg_event to resurrect nohz ratelimiting Mike Galbraith
2011-11-18 15:36                     ` Peter Zijlstra
2011-11-18 17:42                       ` Mike Galbraith
2011-11-19  0:51                         ` Van De Ven, Arjan
2011-11-19  4:15                           ` Mike Galbraith
2011-11-18 15:20                   ` [patch 4/6] sched: ratelimit select_idle_sibling()for sync wakeups Mike Galbraith
2011-11-18 15:22                   ` [patch 5/6] sched: save some hrtick_start_fair cycles Mike Galbraith
2011-11-18 15:23                   ` [patch 6/6] sched: set skip_clock_update in yield_task_fair() Mike Galbraith
2012-02-20 14:41                   ` sched: Avoid SMT siblings in select_idle_sibling() if possible Peter Zijlstra
2012-02-20 15:03                     ` Srivatsa Vaddagiri
2012-02-20 18:25                       ` Mike Galbraith
2012-02-21  0:06                         ` Srivatsa Vaddagiri
2012-02-21  6:37                           ` Mike Galbraith
2012-02-21  8:09                             ` Srivatsa Vaddagiri
2012-02-20 18:14                     ` Mike Galbraith
2012-02-20 18:15                       ` Peter Zijlstra
2012-02-20 19:07                       ` Peter Zijlstra
2012-02-21  5:43                         ` Mike Galbraith
2012-02-21  8:32                           ` Srivatsa Vaddagiri
2012-02-21  9:21                             ` Mike Galbraith
2012-02-21 10:37                               ` Peter Zijlstra
2012-02-21 14:58                                 ` Srivatsa Vaddagiri
2012-02-23 10:49                       ` Srivatsa Vaddagiri
2012-02-23 11:19                         ` Ingo Molnar
2012-02-23 12:18                           ` Srivatsa Vaddagiri
2012-02-23 11:20                         ` Srivatsa Vaddagiri
2012-02-23 11:26                           ` Ingo Molnar
2012-02-23 11:32                             ` Srivatsa Vaddagiri
2012-02-23 16:17                               ` Ingo Molnar
2012-02-23 11:21                         ` Mike Galbraith
2012-02-25  6:54                           ` Srivatsa Vaddagiri
2012-02-25  8:30                             ` Mike Galbraith
2012-02-27 22:11                               ` Suresh Siddha
2012-02-28  5:05                                 ` Mike Galbraith
2011-11-17 19:08             ` Suresh Siddha
2011-11-18 15:12               ` Peter Zijlstra
2011-11-18 15:26                 ` Mike Galbraith
2011-12-06  9:49               ` [tip:sched/core] sched: Clean up domain traversal in select_idle_sibling() tip-bot for Suresh Siddha
2011-11-18 23:40 ` [tip:sched/core] sched: Avoid SMT siblings in select_idle_sibling() if possible tip-bot for Peter Zijlstra

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