linux-kernel - Re: [PATCH 2/7] sched: Update rq clock on nohz CPU before setting fair group shares

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Date:	Wed, 10 Apr 2013 12:06:20 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	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 2/7] sched: Update rq clock on nohz CPU before setting
 fair group shares


* Peter Zijlstra <peterz@...radead.org> wrote:

> I think Mike once tried something along the lines of keeping a per rq state that 
> got cleared at the end of schedule() but that doesn't catch things like the 
> migrate handlers I think.

We'd need a rq->clock.valid debug flag, which is set by a sched-clock update, and 
cleared by the end of all scheduler operations, not just schedule().

Then sched_clock() could have a pretty efficient assert in it. Are there bugs that 
such an approach would not catch?

Thaks,

	Ingo
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