From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:36856) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UIj33-0007so-4F for qemu-devel@nongnu.org; Thu, 21 Mar 2013 13:13:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UIj31-00071S-Kk for qemu-devel@nongnu.org; Thu, 21 Mar 2013 13:13:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:63240) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UIj31-00071J-Bl for qemu-devel@nongnu.org; Thu, 21 Mar 2013 13:13:03 -0400 Message-ID: <514B3F9A.107@redhat.com> Date: Thu, 21 Mar 2013 18:12:58 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <1363881940-27505-1-git-send-email-owasserm@redhat.com> In-Reply-To: <1363881940-27505-1-git-send-email-owasserm@redhat.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v3 0/9] Migration: Remove copying of guest ram pages List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Orit Wasserman Cc: mst@redhat.com, chegu_vinod@hp.com, qemu-devel@nongnu.org, quintela@redhat.com Il 21/03/2013 17:05, Orit Wasserman ha scritto: > In migration all data is copied to a static buffer in QEMUFile, > this hurts our network bandwidth and CPU usage especially with large guests. > We switched to iovec for storing different buffers to send (even a byte field is > considered as a buffer) and use writev to send the iovec. > writev was chosen (as apposed to sendmsg) because it supprts non socket fds. > > Guest memory pages are not copied by calling a new function > qemu_put_buffer_no_copy. > The page header data and device state data are still copied into the static > buffer. This data consists of a lot of bytes and integer fields and the static > buffer is used to store it during batching. > Another improvement is changing qemu_putbe64/32/16 to create a single > buffer instead of several byte sized buffer. > > git repository: git://github.com/oritwas/qemu.git sendv_v2 > > Change from v2: > Always send data for the iovec even if writev_buffer is not implemented. > Coalesce adjacent iovecs to create one big buffer from small adjacent buffer. > > Changes from v1: > Use iov_send for socket. > Make writev_buffer optional and if it is not implemented use put_buffer I didn't review it too closely, so I don't feel like giving my Reviewed-by. Still, I must say it is a very nice and simple solution. Kudos! Just one question: patch 6 is not strictly needed anymore now that you have coalescing, no? Should Juan leave it out? Paolo