Date: Tue, 14 Dec 2010 14:55:35 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: Rik van Riel <riel@redhat.com>
Cc: Avi Kivity <avi@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, Ingo Molnar <mingo@elte.hu>,
        Anthony Liguori <aliguori@linux.vnet.ibm.com>,
        Bharata B Rao <bharata.rao@in.ibm.com>
Subject: Re: [RFC PATCH 0/3] directed yield for Pause Loop Exiting
Message-ID: <20101214092535.GD14178@balbir.in.ibm.com>
Reply-To: balbir@linux.vnet.ibm.com
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 <20101210050344.GR3158@balbir.in.ibm.com>
 <4D0328CC.1020809@redhat.com>
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* Rik van Riel <riel@redhat.com> [2010-12-13 12:02:51]:

> 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.
>

Yes, I personally think so too, but I suspect there needs to be a
larger agreement on the semantics. The VCPU semantics in terms of
power apply to each VCPU as opposed to the entire system (per guest).
 
> 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.

Yes, that seems right!

-- 
	Three Cheers,
	Balbir
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