linux-kernel - Re: + stupid-hack-to-make-mainline-build.patch added to -mm tree

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Message-Id: <1173253716.24738.540.camel@localhost.localdomain>
Date:	Wed, 07 Mar 2007 08:48:36 +0100
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dan Hecht <dhecht@...are.com>
Cc:	Zachary Amsden <zach@...are.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org, ak@...e.de,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	LKML <linux-kernel@...r.kernel.org>,
	john stultz <johnstul@...ibm.com>
Subject: Re: + stupid-hack-to-make-mainline-build.patch added to -mm tree

On Tue, 2007-03-06 at 17:44 -0800, Dan Hecht wrote:
> >>> 2) As I said above. The time accounting for virtualization needs to be
> >>> fixed in a generic way.
> >>>
> >>> I'm not going to accept some weird hackery for virtualization, which is
> >>> of exactly ZERO value for the kernel itself. Quite the contrary it will
> >>> make the cleanup harder and introduce another hard to remove thing,
> >>> which will in the worst case last for ever.
> >>>
> >> Okay, to confirm I'm on the same page as you, you want to move process 
> >> time accounting from being periodic sampled based to being trace based? 
> >> i.e. at the system-call/interrupt boundaries, read clocksource and 
> >> compute directly the amount of system/user/process time?
> > 
> > At least for the paravirt guests this is the correct approach. Once the
> > CPU vendors come up with a sane solution for a reliable and fast clock
> > source we might use that on real hardware as well.
> > 
> 
> I thought your preference was to not do things differently from real 
> hardware?  I guess this case you are okay with since you'd like to see 
> the real hardware case follow eventually?

Real hardware _IS_ broken and slow. If we add the facilities for
virtualization we want it in a way, which is usable by real hardware as
well.

> > Yes, with todays hardware it is simply a PITA. PowerPC has some basic
> > support for this though, IIRC.
> > 
> 
> I think S390 maybe too.

One more reason to make it a generic solution rather than some extra
hackery.

	tglx


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