From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [Xen-devel] [RFC PATCHv1 net-next] xen-netback: always fully coalesce guest Rx packets Date: Mon, 19 Jan 2015 17:36:10 +0000 Message-ID: <54BD408A.6080405@citrix.com> References: <1421157917-31333-1-git-send-email-david.vrabel@citrix.com> <20150113143033.GN4226@zion.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 8bit Cc: , Ian Campbell , , Jonathan Davies To: Wei Liu , David Vrabel Return-path: Received: from smtp02.citrix.com ([66.165.176.63]:14713 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751772AbbASRvb (ORCPT ); Mon, 19 Jan 2015 12:51:31 -0500 In-Reply-To: <20150113143033.GN4226@zion.uk.xensource.com> Sender: netdev-owner@vger.kernel.org List-ID: On 13/01/15 14:30, Wei Liu wrote: > On Tue, Jan 13, 2015 at 02:05:17PM +0000, David Vrabel wrote: >> Always fully coalesce guest Rx packets into the minimum number of ring >> slots. Reducing the number of slots per packet has significant >> performance benefits (e.g., 7.2 Gbit/s to 11 Gbit/s in an off-host >> receive test). >> > > Good number. > >> However, this does increase the number of grant ops per packet which >> decreases performance with some workloads (intrahost VM to VM) > > Do you have figures before and after this change? Some better (more rigorous) results done by Jonathan Davies shows no regressions with full coalescing even without the grant copy optimization, and a big improvement to single stream receive. baseline Full coalesce Interhost aggregate 24 Gb/s 24 Gb/s Interhost VM receive 7.2 Gb/s 11 Gb/s Intrahost single stream 14 Gb/s 14 Gb/s Intrahost aggregate 34 Gb/s 34 Gb/s We do not measure the performance of dom0 to guest traffic but my ad-hoc measurements suggest this may be 5-10% slower. I don't think this is a very important use case though. So... >> /unless/ grant copy has been optimized for adjacent ops with the same >> source or destination (see "grant-table: defer releasing pages >> acquired in a grant copy"[1]). >> >> Do we need to retain the existing path and make the always coalesce >> path conditional on a suitable version of Xen? ...I think the answer to this is no. >> --- >> drivers/net/xen-netback/common.h | 1 - >> drivers/net/xen-netback/netback.c | 106 ++----------------------------------- >> 2 files changed, 3 insertions(+), 104 deletions(-) > > Love the diffstat! Yes, it's always nice when you delete code and it goes faster... :) David