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

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Message-ID: <BC00F5384FCFC9499AF06F92E8B78A9E026FAC6185@shsmsx502.ccr.corp.intel.com>
Date:	Mon, 19 Apr 2010 09:32:12 +0800
From:	"Zhang, Xiantao" <xiantao.zhang@...el.com>
To:	"vatsa@...ibm.com" <vatsa@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Avi Kivity <avi@...hat.com>,
	Srivatsa Vaddagiri <vatsa.ml@...il.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>
Subject: RE: VM performance issue in KVM guests.

Srivatsa Vaddagiri wrote:
> On Thu, Apr 15, 2010 at 03:33:18PM +0200, 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. Para virt
>> kernels could possibly extend the thing by also checking to see if
>> the owner's vcpu is running.
> 
> I suspect we will need a combination of both approaches, given that
> we will not be able to avoid preempting guests in their critical
> section always (too long critical sections or real-time tasks wanting
> to preempt). Other idea is to gang-schedule VCPUs of the same guest
> as much as possible? 
Gang-scheduling maybe the ideal solution to solve the issue, and has to change host's scheduler a lot to implement it, and it maybe hard to be upstream.  So can we figure out an easy way(maybe not best) for this ? 
Xiantao
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