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Subject: Re: max_clock of the patch "sched_clock: fix cpu_clock()"
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Lin Ming <ming.m.lin@intel.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
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Date: Tue, 16 Sep 2008 06:48:30 +0200
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On Tue, 2008-09-16 at 11:01 +0800, Lin Ming wrote:
> Hi, Peter,
> 
> I have a question of the max_clock in below patch,
> commit 354879bb977e06695993435745f06a0f6d39ce2b
> Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Date:   Mon Aug 25 17:15:34 2008 +0200
> 
>     sched_clock: fix cpu_clock()
> 
> The original code to calculate min_clock and max_clock is,
> min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC;
> max_clock = min_clock + TICK_NSEC;
> 
> Now it's changed to,
> min_clock = wrap_max(scd->tick_gtod, scd->clock);
> max_clock = scd->tick_gtod + TICK_NSEC;
> 
> Is this max_clock still correct if, in a rare case, irq is disabled for
> many ticks?

Nope, it wont (nor would the old), but having irqs disabled for that
long would be something worth fixing.