From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC PATCH v1 3/5] KVM: Add paravirt kvm_flush_tlb_others Date: Tue, 01 May 2012 18:33:08 +0300 Message-ID: <4FA00234.1020006@redhat.com> References: <20120427161727.27082.43096.stgit@abhimanyu> <20120427162401.27082.59387.stgit@abhimanyu> <4F9D32B4.8040002@redhat.com> <1335865176.13683.120.camel@twins> <4F9FBF38.2060903@redhat.com> <1335869827.13683.133.camel@twins> <4F9FD337.5010908@redhat.com> <1335885103.13683.147.camel@twins> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Nikunj A. Dadhania" , mingo@elte.hu, jeremy@goop.org, mtosatti@redhat.com, kvm@vger.kernel.org, x86@kernel.org, vatsa@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, hpa@zytor.com To: Peter Zijlstra Return-path: Received: from mx1.redhat.com ([209.132.183.28]:30038 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757111Ab2EAPd3 (ORCPT ); Tue, 1 May 2012 11:33:29 -0400 In-Reply-To: <1335885103.13683.147.camel@twins> Sender: kvm-owner@vger.kernel.org List-ID: On 05/01/2012 06:11 PM, Peter Zijlstra wrote: > On Tue, 2012-05-01 at 15:12 +0300, Avi Kivity wrote: > > We're now moving the freeing of kvm shadow page tables from using rcu to > > using an irq-protected scheme like gup_fast(), because of the > > performance differences. We didn't track it down but I expect the cause > > is less reuse of cache-hot pages. > > It would be good to understand these things.. just doing things because > tends to come back and bite you :-) Agree. Anyway that was only part of the motivation, the other part was establishing a bound on the number of pages under deferred freeing. > If its cache behaviour you should be able to clearly see that using perf > stat. It's hard to see it clearly because the changes are in the order of 1-2% in a very noisy benchmark. -- error compiling committee.c: too many arguments to function