linux-kernel - Re: VM performance issue in KVM guests.

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Message-ID: <4BCA0646.1000603@redhat.com>
Date:	Sat, 17 Apr 2010 22:04:38 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Srivatsa Vaddagiri <vatsa.ml@...il.com>,
	"Zhang, Xiantao" <xiantao.zhang@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	"Yang, Xiaowei" <xiaowei.yang@...el.com>,
	"Dong, Eddie" <eddie.dong@...el.com>, "Li, Xin" <xin.li@...el.com>,
	Ingo Molnar <mingo@...e.hu>, Mike Galbraith <efault@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	vatsa@...ux.vnet.ibm.com
Subject: Re: VM performance issue in KVM guests.

On 04/15/2010 04:33 PM, Peter Zijlstra wrote:
> On Thu, 2010-04-15 at 11:18 +0300, Avi Kivity wrote:
>    
>> Certainly that has even greater potential for Linux guests.  Note that
>> we spin on mutexes now, so we need to prevent preemption while the lock
>> owner is running.
>>      
> either that, or disable spinning on (para) virt kernels.

What would you do instead?

Note we can't disable spinning on Windows or pre 2.6.36 kernels.

> Para virt
> kernels could possibly extend the thing by also checking to see if the
> owner's vcpu is running.
>    

Certainly that's worth doing.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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