From: Peter Zijlstra <peterz@infradead.org>
To: Chris Redpath <chris.redpath@arm.com>
Cc: "pjt@google.com" <pjt@google.com>,
"mingo@redhat.com" <mingo@redhat.com>,
"alex.shi@linaro.org" <alex.shi@linaro.org>,
Morten Rasmussen <Morten.Rasmussen@arm.com>,
Dietmar Eggemann <Dietmar.Eggemann@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
bsegall@google.com
Subject: Re: [PATCH 2/2] sched: update runqueue clock before migrations away
Date: Tue, 10 Dec 2013 16:14:28 +0100 [thread overview]
Message-ID: <20131210151428.GH12849@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <52A71605.5090509@arm.com>
On Tue, Dec 10, 2013 at 01:24:21PM +0000, Chris Redpath wrote:
> What happens is that if you have a task which sleeps for a while and wakes
> on a different CPU and the previous CPU hasn't had a tick for a while, then
> that sleep time is lost.
/me more confused now.
Where does update_cfs_rq_blocked_load() account sleep time? Its only
concerned with the blocked decay.
Or is it the decay_count <= 0 case in enqueue_entity_load_avg() that's
screwing you over?
That's guestimating the last_runnable_update based on decay_count, and
per the previous the decay count can get slightly out of sync.
If so, we should look to cure the issue enqueue_entity_load_avg() is
trying to work around, namely the fact that we cannot assume synced
clocks, nor can we read remote clocks atomically.
next prev parent reply other threads:[~2013-12-10 15:14 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-09 12:59 [PATCH 0/2] Per-task load tracking errors Chris Redpath
2013-12-09 12:59 ` [PATCH 1/2] sched: reset blocked load decay_count during synchronization Chris Redpath
2013-12-09 17:59 ` bsegall
2013-12-09 12:59 ` [PATCH 2/2] sched: update runqueue clock before migrations away Chris Redpath
2013-12-09 18:13 ` bsegall
2013-12-10 11:48 ` Peter Zijlstra
2013-12-10 13:24 ` Chris Redpath
2013-12-10 15:14 ` Peter Zijlstra [this message]
2013-12-10 15:55 ` Chris Redpath
2013-12-12 18:24 ` Peter Zijlstra
2013-12-13 8:48 ` Vincent Guittot
2013-12-17 14:09 ` Chris Redpath
2013-12-17 15:51 ` Peter Zijlstra
2013-12-17 18:03 ` bsegall
2013-12-18 10:13 ` Chris Redpath
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