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

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Date:	Thu, 05 Apr 2007 14:50:34 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Daniel Walker <dwalker@...sta.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu
Subject: Re: [PATCH] timekeeping: drop irq-context clocksource polling

On Thu, 2007-04-05 at 14:36 -0700, Andrew Morton wrote:
> On Thu, 05 Apr 2007 14:25:19 -0700
> john stultz <johnstul@...ibm.com> wrote:
> 
> > On Thu, 2007-04-05 at 14:03 -0700, Daniel Walker 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.
> > > 
> > > This also has a few small space and line cleanups.
> > > 
> > > Boot tested on i386, compile tested on x86_64 .. However, I couldn't
> > > find a !GENERIC_TIME that compiled without this change so it's untested..
> > > 
> > > Signed-Off-By: Daniel Walker <dwalker@...sta.com>
> > 
> > Err.. I think you need to be holding a write on the xtime_lock (as is
> > done before calling update_wall_time()) when changing the clocksource.
> 
> The patch does add the appropriate locking to change_clocksource(),
> doesn't it?

Yep. Sorry for the confusion, reading too hastily. 

> It looks like a good change to me - we avoid taking the kernel-wide
> clocksource_lock every tick?

Agreed.

Acked-by: John Stultz <johnstul@...ibm.com>

-john


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