linux-kernel - Re: [RFC][PATCH v2 4/7] taskstats: Add per task steal time accounting

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Message-ID: <20101116170549.05d9e5c6@mschwide.boeblingen.de.ibm.com>
Date:	Tue, 16 Nov 2010 17:05:49 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Shailabh Nagar <nagar1234@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...hat.com>,
	John stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	"jeremy.fitzhardinge" <jeremy.fitzhardinge@...rix.com>,
	Avi Kivity <avi@...hat.com>
Subject: Re: [RFC][PATCH v2 4/7] taskstats: Add per task steal time
 accounting

On Tue, 16 Nov 2010 16:45:29 +0100
Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> > > Except that the per-task steal time gives you lot less detail, being
> > > able to profile on vcpu exit/enter gives you a much more powerfull
> > > performance tool. Aside from being able to measure the steal-time it
> > > allows you to instantly find hypercalls (both explicit as well as
> > > implicit), so you can also measure the hypercall induced steal-time as
> > > well.
> > 
> > Yes and no. The tracepoint idea looks interesting in itself. But that does
> > not completely replace the per-task steal time. The hypervisor can take
> > away the cpu anytime, it is still interesting to know which task was hit
> > hardest by that. You could view the cpu time lost by a hypercall as
> > "synchronous" steal time for the task, the remaining delta to the total
> > per-task steal time as "asynchronous" steal time. 
> 
> Right, so there is no way the guest knows about the vcpu getting
> scheduled, it can only derive the fact from hardware clocks after the
> fact?

Correct.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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