From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=38508 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OHbso-0004r8-2e for qemu-devel@nongnu.org; Thu, 27 May 2010 08:08:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OHbsm-0000q3-Pv for qemu-devel@nongnu.org; Thu, 27 May 2010 08:08:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34703) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OHbsm-0000pL-I6 for qemu-devel@nongnu.org; Thu, 27 May 2010 08:08:16 -0400 Message-ID: <4BFE6098.9010000@redhat.com> Date: Thu, 27 May 2010 15:07:52 +0300 From: Avi Kivity MIME-Version: 1.0 References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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, Rusty Russell , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org On 05/26/2010 10:50 PM, 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. > > Generally, the Host end of the virtio ring doesn't need to see where > Guest is up to in consuming the ring. However, to completely understand > what's going on from the outside, this information must be exposed. > For example, host can reduce the number of interrupts by detecting > that the guest is currently handling previous buffers. > > We add a feature bit so the guest can tell the host that it's writing > out the current value there, if it wants to use that. > > This differs from original approach in that the used index > is put after avail index (they are typically written out together). > To avoid cache bounces on descriptor access, > and make future extensions easier, we put the ring itself at start of > page, and move the control after it. > I missed the spec patch, can you repost it? -- error compiling committee.c: too many arguments to function