Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756372Ab2BANyZ (ORCPT ); Wed, 1 Feb 2012 08:54:25 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45014 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754370Ab2BANyW (ORCPT ); Wed, 1 Feb 2012 08:54:22 -0500 Date: Wed, 1 Feb 2012 11:43:47 -0200 From: Marcelo Tosatti To: Avi Kivity Cc: Takuya Yoshikawa , Peter Zijlstra , paulmck@linux.vnet.ibm.com, Oleg Nesterov , linux-kernel , KVM list Subject: Re: [RFC][PATCH] srcu: Implement call_srcu() Message-ID: <20120201134347.GA18998@amt.cnet> References: <1328016724.2446.229.camel@twins> <4F27F0E6.1040309@redhat.com> <1328017807.2446.230.camel@twins> <20120131222447.GH2391@linux.vnet.ibm.com> <1328091749.2760.34.camel@laptop> <4F29178A.1090306@redhat.com> <4F2918D5.4050104@redhat.com> <4F291B56.30600@oss.ntt.co.jp> <4F291B92.8070402@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F291B92.8070402@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1289 Lines: 46 On Wed, Feb 01, 2012 at 01:01:38PM +0200, Avi Kivity wrote: > On 02/01/2012 01:00 PM, Takuya Yoshikawa wrote: > > > >> rcu_assign_pointer), and use atomic operations to copy and clear: > >> > >> word = bitmap[i] > >> put_user(word) > >> atomic_and(&bitmap[i], ~word) > >> > >> > > > > This kind of this was really slow IIRC. > > > > > > How about just doing: > > > > take a spin_lock > > copy the entire (or some portions of) bitmap locally > > clear the bitmap > > unlock > > > > That means that vcpus dirtying memory also have to take that lock, and > spin while the bitmap is being copied. So kvm_vm_ioctl_get_dirty_log() > will become faster, at the expense of vcpus, which I think is a bad > tradeoff. > > > write protect the dirty pages based on the copied dirty data > > > > copy_to_user > > > > > > > > I can show you some performance numbers, this weekend, if you like. > > That'll be great, numbers are better than speculation. get dirty log: 5634134 ns for 262144 dirty pages 5ms (for the entire operation). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/