linux-kernel - Re: [BUG] 2.6.37-rc3 massive interactivity regression on ARM

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Message-ID: <1291917330.6803.7.camel@twins>
Date:	Thu, 09 Dec 2010 18:55:30 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Venkatesh Pallipadi <venki@...gle.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Mikael Pettersson <mikpe@...uu.se>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	John Stultz <johnstul@...ibm.com>
Subject: Re: [BUG] 2.6.37-rc3 massive interactivity regression on ARM

On Thu, 2010-12-09 at 09:43 -0800, Venkatesh Pallipadi wrote:
> 
> The same problem will be there with below code, with irq_delta >
> delta, clock_task can go backwards which is not good.
> +       delta -= irq_delta;
> +       rq->clock_task += delta;
> 
> The reason for this is rq->clock and irqtime updates kind of happen
> independently and specifically, if a rq->clock update happens while we
> are in a softirq, we may have this case of going backwards on the next
> update.

But how can irq_delta > delta?, we measure it using the same clock.
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