From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 2/2] KVM: Convert read-only users of vm_list to RCU Date: Thu, 10 Feb 2011 14:57:13 +0200 Message-ID: <4D53E0A9.2030501@redhat.com> References: <4D512EF7.8040409@siemens.com> <4D512F3B.1080107@siemens.com> <4D53BB02.20206@redhat.com> <4D53CCAB.8040204@siemens.com> <4D53DB54.90605@redhat.com> <4D53DDD3.5020704@siemens.com> <4D53E063.1040004@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , kvm , Zachary Amsden To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:1558 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752268Ab1BJM5S (ORCPT ); Thu, 10 Feb 2011 07:57:18 -0500 In-Reply-To: <4D53E063.1040004@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 02/10/2011 02:56 PM, Avi Kivity wrote: >> What's the benefit? The downside is a bit more complexity as you need an >> additional callback handler. > > > synchronize_rcu() can be very slow (its a systemwide operation), and > mmu_shrink() can be called often on a loaded system. > In fact this just shows that vm_list is not a good candidate for rcu; rcu is useful where most operations are reads, but if we discount stats, most operations on vm_list are going to be writes. -- error compiling committee.c: too many arguments to function