linux-kernel - Re: [PATCH 3/7] sched: Update rq clock on tickless CPUs before calling check_preempt

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Message-ID: <CAFTL4hzx5ctiEDh2Q77D+09XuQsZkajbf_bN4BJKdwgBkmCLZw@mail.gmail.com>
Date:	Tue, 9 Apr 2013 18:53:13 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung.kim@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>, Mike Galbraith <efault@....de>
Subject: Re: [PATCH 3/7] sched: Update rq clock on tickless CPUs before
 calling check_preempt_curr()

2013/4/9 Peter Zijlstra <peterz@...radead.org>:
> On Sat, 2013-04-06 at 18:45 +0200, Frederic Weisbecker wrote:
>> check_preempt_wakeup() of fair class needs an uptodate sched clock
>> value to update runtime stats of the current task.
>>
>> When a task is woken up, activate_task() is usually called right
>> before
>> ttwu_do_wakeup() unless the task is still in the runqueue. In this
>> case we need to update the rq clock manually in case the CPU runs
>> tickless because ttwu_do_wakeup() calls check_preempt_wakeup().
>
> again, same story.. I think the entire nohz specific clock update stuff
> is completely broken and you're finding sites that are simply missing
> clock updates.
>

Agreed!
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