linux-kernel - Re: [PATCH 5/7] KVM-GST: KVM Steal time accounting

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Message-ID: <1308130102.15315.17.camel@twins>
Date:	Wed, 15 Jun 2011 11:28:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Glauber Costa <glommer@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Rik van Riel <riel@...hat.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Avi Kivity <avi@...hat.com>,
	Anthony Liguori <aliguori@...ibm.com>,
	Eric B Munson <emunson@...bm.net>
Subject: Re: [PATCH 5/7] KVM-GST: KVM Steal time accounting

On Tue, 2011-06-14 at 22:08 -0300, Glauber Costa wrote:
> >> +               while (steal>  TICK_NSEC) {
> >
> >                       /* really, if we wanted a division we'd have
> written one */
> >                       asm("" : "+rm" (steal));
> 
> Out of curiosity, have we seen any compiler de-optimize it to a 
> division, or are you just being careful ?
> 
> >> +                       steal -= TICK_NSEC;
> >> +                       st++;
> >> +               } 

No that really happened a number of times, there's one in
sched_avg_period() that actually triggered and __iter_div_u64_rem() that
started it all iirc.
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