From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: Re: Performance of 40-way guest running 2.6.32-220 (RHEL6.2) vs. 3.3.1 OS Date: Thu, 12 Apr 2012 14:21:06 -0400 Message-ID: <4F871D12.3060006@redhat.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, Gleb Natapov To: Chegu Vinod Return-path: Received: from mx1.redhat.com ([209.132.183.28]:26256 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932317Ab2DLSU6 (ORCPT ); Thu, 12 Apr 2012 14:20:58 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 04/11/2012 01:21 PM, Chegu Vinod wrote: > > Hello, > > While running an AIM7 (workfile.high_systime) in a single 40-way (or a single > 60-way KVM guest) I noticed pretty bad performance when the guest was booted > with 3.3.1 kernel when compared to the same guest booted with 2.6.32-220 > (RHEL6.2) kernel. > For the 40-way Guest-RunA (2.6.32-220 kernel) performed nearly 9x better than > the Guest-RunB (3.3.1 kernel). In the case of 60-way guest run the older guest > kernel was nearly 12x better ! > Turned on function tracing and found that there appears to be more time being > spent around the lock code in the 3.3.1 guest when compared to the 2.6.32-220 > guest. Looks like you may be running into the ticket spinlock code. During the early RHEL 6 days, Gleb came up with a patch to automatically disable ticket spinlocks when running inside a KVM guest. IIRC that patch got rejected upstream at the time, with upstream developers preferring to wait for a "better solution". If such a better solution is not on its way upstream now (two years later), maybe we should just merge Gleb's patch upstream for the time being?