linux-kernel - Re: [RFC PATCH 0/3] directed yield for Pause Loop Exiting

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Date:	Mon, 13 Dec 2010 12:02:51 -0500
From:	Rik van Riel <riel@...hat.com>
To:	balbir@...ux.vnet.ibm.com
CC:	Avi Kivity <avi@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Anthony Liguori <aliguori@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 0/3] directed yield for Pause Loop Exiting

On 12/11/2010 08:57 AM, Balbir Singh wrote:

> If the vpcu holding the lock runs more and capped, the timeslice
> transfer is a heuristic that will not help.

That indicates you really need the cap to be per guest, and
not per VCPU.

Having one VCPU spin on a lock (and achieve nothing), because
the other one cannot give up the lock due to hitting its CPU
cap could lead to showstoppingly bad performance.

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