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

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Message-Id: <1176021199.28263.529.camel@localhost.localdomain>
Date:	Sun, 08 Apr 2007 10:33:19 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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 14:30 -0700, Daniel Walker wrote:
> On Sat, 2007-04-07 at 22:50 +0200, Thomas Gleixner wrote:
> > On Sat, 2007-04-07 at 10:43 -0700, Daniel Walker wrote:
> > > 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 .
> > 
> > Simply because it fiddles with variables which are relevant for
> > timekeeping.
> 
> loops_per_jiffy perhaps?

Oh well, this is a leftover from the days where we tried to use TSC
despite of frequency changes. It still modifies the scale factor of the
tsc clocksource. 

I agree that it can be removed as we switch off TSC anyway in that case.

	tglx


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