linux-kernel - Re: [RFC] clocksouce implementation for powerpc

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Date:	Fri, 22 Jun 2007 16:23:05 +1000
From:	tony@...eyournoodle.com (Tony Breeds)
To:	Daniel Walker <dwalker@...sta.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>,
	john stultz <johnstul@...ibm.com>,
	LinuxPPC-dev <linuxppc-dev@...abs.org>
Subject: Re: [RFC] clocksouce implementation for powerpc

On Wed, Jun 20, 2007 at 07:57:19AM -0700, Daniel Walker wrote:

Hi Daniel.

> As I said in our private thread, I do think you should be using
> update_vsyscall() .. update_vsyscall() is just called when the time is
> set, usually that happens in the timer interrupt and sometimes that
> happens in settimeofday() ..

Well I've taken another look at the code and I think I can probably
restructure my code to use update_vsyscall().  I thought I needed a
hook that was called /only/ from settimeofday() (which as you say
doesn't match update_vsyscall()'s usage).

I'll try again and see what problems I hit.
 
> At least some of your code is duplications over what is already being
> worked on inside the powerpc community.. For instance, I know there is
> already a timebase clocksource,
> 
> http://people.redhat.com/~mingo/realtime-preempt/patch-2.6.21.5-rt17

Thanks. The one in -rt doesn't seem to support the VDSO.  however I see
that there is duplication of effort there.
 
> Hmm .. This doesn't look like it's taking into account that the time has
> changed .. Your time has effectively incremented by one jiffie .. The
> vdso_data doesn't appear to be updated ..

Unless I miss your meaning, the vdso is updated in
timer_recalc_offset()/update_gtod() when needed.

Yours Tony

  linux.conf.au        http://linux.conf.au/ || http://lca2008.linux.org.au/
  Jan 28 - Feb 02 2008 The Australian Linux Technical Conference!

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