From: Wanpeng Li <kernellwp@gmail.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
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>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH 2/3] sched: Correctly handle nohz ticks cpu load accounting
Date: Wed, 20 Apr 2016 15:59:43 +0800 [thread overview]
Message-ID: <CANRm+CyZtgAXEvnX76Jh5uJwvbYuJnKrkzUXa4jFKnBLSvtb1Q@mail.gmail.com> (raw)
In-Reply-To: <1460555812-25375-3-git-send-email-fweisbec@gmail.com>
Hi Frederic,
2016-04-13 21:56 GMT+08:00 Frederic Weisbecker <fweisbec@gmail.com>:
> Ticks can happen while the CPU is in dynticks-idle or dynticks-singletask
> mode. In fact "nohz" or "dynticks" only mean that we exit the periodic
> mode and we try to minimize the ticks as much as possible. The nohz
> subsystem uses a confusing terminology with the internal state
> "ts->tick_stopped" which is also available through its public interface
> with tick_nohz_tick_stopped(). This is a misnomer as the tick is instead
> reduced with the best effort rather than stopped. In the best case the
> tick can indeed be actually stopped but there is no guarantee about that.
> If a timer needs to fire one second later, a tick will fire while the
> CPU is in nohz mode and this is a very common scenario.
>
> Now this confusion happens to be a problem with cpu load updates:
> cpu_load_update_active() doesn't handle nohz ticks correctly because it
> assumes that ticks are completely stopped in nohz mode and that
> cpu_load_update_active() can't be called in dynticks mode. When that
> happens, the whole previous tickless load is ignored and the function
> just records the load for the current tick, ignoring potentially long
> idle periods behind.
This is for one timer interrupt per second scenario, right?
Regards,
Wanpeng Li
next prev parent reply other threads:[~2016-04-20 7:59 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-13 13:56 [PATCH 0/3] sched: Fix/improve nohz cpu load updates v3 Frederic Weisbecker
2016-04-13 13:56 ` [PATCH 1/3] sched: Gather cpu load functions under a more conventional namespace Frederic Weisbecker
2016-04-23 12:58 ` [tip:sched/core] sched/fair: Gather CPU " tip-bot for Frederic Weisbecker
2016-04-13 13:56 ` [PATCH 2/3] sched: Correctly handle nohz ticks cpu load accounting Frederic Weisbecker
2016-04-18 8:22 ` Byungchul Park
2016-04-18 9:17 ` Byungchul Park
2016-04-18 13:35 ` Frederic Weisbecker
2016-04-19 0:01 ` Byungchul Park
2016-04-19 14:01 ` Frederic Weisbecker
2016-04-20 7:59 ` Wanpeng Li [this message]
2016-04-23 12:59 ` [tip:sched/core] sched/fair: Correctly handle nohz ticks CPU " tip-bot for Frederic Weisbecker
2016-04-13 13:56 ` [PATCH 3/3] sched: Optimize !CONFIG_NO_HZ_COMMON cpu load updates Frederic Weisbecker
2016-04-18 13:36 ` Frederic Weisbecker
2016-04-19 15:36 ` [PATCH v2] " Frederic Weisbecker
2016-04-23 12:59 ` [tip:sched/core] sched/fair: Optimize !CONFIG_NO_HZ_COMMON CPU " tip-bot for Frederic Weisbecker
-- strict thread matches above, loose matches on Subject: below --
2016-04-08 1:07 [PATCH 0/3] sched: Fix/improve nohz cpu load updates v2 Frederic Weisbecker
2016-04-08 1:07 ` [PATCH 2/3] sched: Correctly handle nohz ticks cpu load accounting Frederic Weisbecker
2016-04-08 9:41 ` Peter Zijlstra
2016-04-08 12:53 ` Frederic Weisbecker
2016-04-08 17:40 ` Peter Zijlstra
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