From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756275Ab0EaHqx (ORCPT ); Mon, 31 May 2010 03:46:53 -0400 Received: from ozlabs.org ([203.10.76.45]:60614 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754981Ab0EaHqv (ORCPT ); Mon, 31 May 2010 03:46:51 -0400 From: Rusty Russell To: "Michael S. Tsirkin" Subject: Re: [PATCHv2-RFC 0/2] virtio: put last seen used index into ring itself Date: Mon, 31 May 2010 17:16:42 +0930 User-Agent: KMail/1.13.2 (Linux/2.6.32-21-generic; KDE/4.4.2; i686; ; ) Cc: linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, qemu-devel@nongnu.org References: In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201005311716.43573.rusty@rustcorp.com.au> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 27 May 2010 05:20:35 am Michael S. Tsirkin wrote: > Here's a rewrite of the original patch with a new layout. > I haven't tested it yet so no idea how this performs, but > I think this addresses the cache bounce issue raised by Avi. > Posting for early flames/comments. Sorry, not without some evidence that it'll actually reduce cacheline bouncing. I *think* it will, but it's not obvious: the host may keep looking at avail_idx as we're updating last_seen. Or does qemu always look at both together anyway? Can someone convince me this is a win? Rusty. From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=47438 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OIzi4-0004OV-CV for qemu-devel@nongnu.org; Mon, 31 May 2010 03:46:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OIzi3-0003bq-CD for qemu-devel@nongnu.org; Mon, 31 May 2010 03:46:56 -0400 Received: from ozlabs.org ([203.10.76.45]:54153) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OIzi3-0003bT-20 for qemu-devel@nongnu.org; Mon, 31 May 2010 03:46:55 -0400 From: Rusty Russell Date: Mon, 31 May 2010 17:16:42 +0930 References: In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201005311716.43573.rusty@rustcorp.com.au> Subject: [Qemu-devel] Re: [PATCHv2-RFC 0/2] virtio: put last seen used index into ring itself List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org On Thu, 27 May 2010 05:20:35 am Michael S. Tsirkin wrote: > Here's a rewrite of the original patch with a new layout. > I haven't tested it yet so no idea how this performs, but > I think this addresses the cache bounce issue raised by Avi. > Posting for early flames/comments. Sorry, not without some evidence that it'll actually reduce cacheline bouncing. I *think* it will, but it's not obvious: the host may keep looking at avail_idx as we're updating last_seen. Or does qemu always look at both together anyway? Can someone convince me this is a win? Rusty.