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

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Message-Id: <20070405143641.a751f43e.akpm@linux-foundation.org>
Date:	Thu, 5 Apr 2007 14:36:41 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	john stultz <johnstul@...ibm.com>
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, 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?

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

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