linux-kernel - Re: 'global' rq->clock

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Message-Id: <1209766054.6929.29.camel@lappy>
Date:	Sat, 03 May 2008 00:07:34 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	David Miller <davem@...emloft.net>
Cc:	efault@....de, elendil@...net.nl, parag.warudkar@...il.com,
	mingo@...e.hu, linux-kernel@...r.kernel.org, guichaz@...oo.fr,
	andi@...stfloor.org
Subject: Re: 'global' rq->clock

On Fri, 2008-05-02 at 14:48 -0700, David Miller wrote:
> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Fri, 02 May 2008 21:56:26 +0200
> 
> > Ok, the the below would need something that relates tick_timestamp's to
> > one another.. probably sucks without it..
> > 
> > OTOH, Andi said he was working on a fastish global sched_clock() thingy,
> > Andi got a link to that code?
> 
> While I'm fine with this kind of stuff being added to constantly cope
> with x86's joke of a TSC register implementation, it's starting to
> become an enormous burdon for platforms where the TICK source actually
> works properly.
> 
> Heck, on my Niagara2 chips, all 64 cpus use the same physical register
> for the TICK source, it physically can't get desynchronized :-)
> 
> So, a way to turn all of this muck off would be much appreciated.
> I'm happy to test anything on sparc64, and I'm sure the powerpc
> folks are as well.
> 
> And I also heard a rumor that Peter has access to a machine with a
> stable tick source for testing :-)

Yeah, I was thinking of a way for architectures to signify how much help
they need building the various clocks. Sparc, power and s390 would not
need any help.

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