linux-kernel - Re: [PATCH] timekeeping: drop irq-context clocksource polling

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Date:	Sat, 07 Apr 2007 10:43:59 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, johnstul@...ibm.com, mingo@...e.hu
Subject: Re: [PATCH] timekeeping: drop irq-context clocksource polling

On Sat, 2007-04-07 at 03:19 -0700, Andrew Morton wrote:
> On Thu, 05 Apr 2007 14:03:16 -0700 Daniel Walker <dwalker@...sta.com> wrote:
> 
> > Before this change the timekeeping code would poll the clocksource
> > list every interrupt. This changes that so the clocksource list is
> > only checked when there has been and update, and no longer checks
> > in interrupt context.
> 
> I get a complete lockup on i386 SMP - before the kernel has printed anything.
> 
> I'm suspecting a recursive taking of xtime_lock.

Looks like this path ,

arch/i386/kernel/tsc.c: time_cpufreq_notifier(); <-- takes xtime_lock
			 mark_tsc_unstable();
            		  clocksource_change_rating(&clocksource_tsc, 0);
			   timekeeping_change_clocksource(); <-- takes xtime_lock


I'm not sure why the time_cpufreq_notifier is taking the xtime_lock tho .

Daniel

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