From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Byungchul Park <byungchul.park@lge.com>,
Chris Metcalf <cmetcalf@ezchip.com>,
Thomas Gleixner <tglx@linutronix.de>,
Luiz Capitulino <lcapitulino@redhat.com>,
Christoph Lameter <cl@linux.com>,
"Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
Mike Galbraith <efault@gmx.de>, Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH 1/4] sched: Don't account tickless CPU load on tick
Date: Tue, 19 Jan 2016 17:22:11 +0100 [thread overview]
Message-ID: <20160119162210.GA5317@lerouge> (raw)
In-Reply-To: <20160119130857.GC6344@twins.programming.kicks-ass.net>
On Tue, Jan 19, 2016 at 02:08:57PM +0100, Peter Zijlstra wrote:
> On Wed, Jan 13, 2016 at 05:01:28PM +0100, Frederic Weisbecker wrote:
> > The cpu load update on tick doesn't care about dynticks and as such is
> > buggy when occuring on nohz ticks (including idle ticks) as it resets
> > the jiffies snapshot that was recorded on nohz entry. We eventually
> > ignore the potentially long tickless load that happened before the
> > tick.
>
> I don't get it, how can we call scheduler_tick() while
> tick_nohz_tick_stopped() ?
tick_nohz_tick_stopped() (which is ts->tick_stopped == 1) doesn't actually
mean that the tick is really stopped. It just means that the tick fires only
when it's really needed (timer list expired, RCU stuff, irq_work, ...). So
if you're lucky, the tick is really stopped because there is nothing that needs
the tick in the future, otherwise (and it's probably most of the time) there is
some tick that may well be programmed some time ahead in the future.
So that's the kind of tick that can break the accounting of a whole long tickless
load that just ran.
next prev parent reply other threads:[~2016-01-19 16:22 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-13 16:01 [RFC PATCH 0/4] sched: Improve cpu load accounting with nohz Frederic Weisbecker
2016-01-13 16:01 ` [PATCH 1/4] sched: Don't account tickless CPU load on tick Frederic Weisbecker
2016-01-19 13:08 ` Peter Zijlstra
2016-01-19 16:22 ` Frederic Weisbecker [this message]
2016-01-19 18:56 ` Peter Zijlstra
2016-01-19 22:33 ` Frederic Weisbecker
2016-01-20 5:43 ` Byungchul Park
2016-01-20 10:26 ` Byungchul Park
2016-01-28 16:01 ` Frederic Weisbecker
2016-01-29 9:50 ` Peter Zijlstra
2016-02-01 10:05 ` Byungchul Park
2016-02-01 10:09 ` [PATCH] sched: calculate sched_clock_cpu without tick handling during nohz Byungchul Park
2016-02-01 10:34 ` [PATCH 1/4] sched: Don't account tickless CPU load on tick Peter Zijlstra
2016-02-01 23:51 ` Byungchul Park
2016-02-02 0:50 ` Byungchul Park
2016-02-01 6:33 ` Byungchul Park
2016-01-20 8:42 ` Thomas Gleixner
2016-01-20 17:36 ` Frederic Weisbecker
2016-01-22 8:40 ` Byungchul Park
2016-01-13 16:01 ` [PATCH 2/4] sched: Consolidate nohz CPU load update code Frederic Weisbecker
2016-01-14 2:30 ` Byungchul Park
2016-01-19 13:13 ` Peter Zijlstra
2016-01-20 0:51 ` Byungchul Park
2016-01-14 5:18 ` Byungchul Park
2016-01-19 13:13 ` Peter Zijlstra
2016-01-19 16:49 ` Frederic Weisbecker
2016-01-20 1:41 ` Byungchul Park
2016-02-29 11:14 ` [tip:sched/core] sched/fair: " tip-bot for Frederic Weisbecker
2016-01-13 16:01 ` [RFC PATCH 3/4] sched: Move cpu load stats functions above fair queue callbacks Frederic Weisbecker
2016-01-13 16:01 ` [RFC PATCH 4/4] sched: Upload nohz full CPU load on task enqueue/dequeue Frederic Weisbecker
2016-01-19 13:17 ` Peter Zijlstra
2016-01-19 17:03 ` Frederic Weisbecker
2016-01-20 9:09 ` Peter Zijlstra
2016-01-20 14:54 ` Frederic Weisbecker
2016-01-20 15:11 ` Thomas Gleixner
2016-01-20 15:19 ` Christoph Lameter
2016-01-20 16:52 ` Frederic Weisbecker
2016-01-20 16:45 ` Frederic Weisbecker
2016-01-20 16:56 ` Peter Zijlstra
2016-01-20 17:21 ` Frederic Weisbecker
2016-01-20 18:25 ` Peter Zijlstra
2016-01-21 13:25 ` Frederic Weisbecker
2016-01-20 9:03 ` Thomas Gleixner
2016-01-20 14:31 ` Frederic Weisbecker
2016-01-20 14:43 ` Thomas Gleixner
2016-01-20 16:40 ` Frederic Weisbecker
2016-01-20 16:42 ` Christoph Lameter
2016-01-20 16:47 ` Frederic Weisbecker
2016-01-14 21:19 ` [RFC PATCH 0/4] sched: Improve cpu load accounting with nohz Dietmar Eggemann
2016-01-14 21:27 ` Peter Zijlstra
2016-01-14 22:23 ` Dietmar Eggemann
2016-01-15 7:07 ` Byungchul Park
2016-01-15 16:56 ` Dietmar Eggemann
2016-01-18 0:23 ` Byungchul Park
2016-01-19 13:04 ` Peter Zijlstra
2016-01-20 0:48 ` Byungchul Park
2016-01-20 13:04 ` Dietmar Eggemann
2016-02-29 11:14 ` [tip:sched/core] sched/fair: Avoid using decay_load_missed() with a negative value tip-bot for Byungchul Park
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