From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: VM performance issue in KVM guests.
Date: Sat, 17 Apr 2010 22:04:38 +0300
Message-ID: <4BCA0646.1000603@redhat.com>
References: <EB8593BCECAB3D40A8248BE0B6400A3846903F4C@shzsmsx502.ccr.corp.intel.com>	 <4BC0D125.9050108@redhat.com>	 <EB8593BCECAB3D40A8248BE0B6400A384690419B@shzsmsx502.ccr.corp.intel.com>	 <4BC2C07B.4040607@redhat.com>	 <p2o2eae271004142158xaa5da968ueff0c2afe6894f9d@mail.gmail.com>	 <4BC6CBE3.8020207@redhat.com> <1271338398.1674.13.camel@laptop>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Cc: Srivatsa Vaddagiri <vatsa.ml@gmail.com>,
	"Zhang, Xiantao" <xiantao.zhang@intel.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	"Yang, Xiaowei" <xiaowei.yang@intel.com>,
	"Dong, Eddie" <eddie.dong@intel.com>, "Li, Xin" <xin.li@intel.com>,
	Ingo Molnar <mingo@elte.hu>, Mike Galbraith <efault@gmx.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	vatsa@linux.vnet.ibm.com
To: Peter Zijlstra <peterz@infradead.org>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <1271338398.1674.13.camel@laptop>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

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.