From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH net-next 2/2] openvswitch: Use zerocopy if applicable when performing the upcall Date: Fri, 24 May 2013 14:57:01 -0700 Message-ID: <1369432621.3301.445.camel@edumazet-glaptop> References: <064a09fffe48540b66a3ee503860ed9e8a1eb5f1.1369406826.git.tgraf@suug.ch> <1369421900.3301.431.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Thomas Graf , netdev , "dev@openvswitch.org" To: Jesse Gross Return-path: Received: from mail-pa0-f49.google.com ([209.85.220.49]:45885 "EHLO mail-pa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755400Ab3EXV5D (ORCPT ); Fri, 24 May 2013 17:57:03 -0400 Received: by mail-pa0-f49.google.com with SMTP id bi5so4723031pad.8 for ; Fri, 24 May 2013 14:57:02 -0700 (PDT) In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Fri, 2013-05-24 at 14:23 -0700, Jesse Gross wrote: > On Fri, May 24, 2013 at 11:58 AM, Eric Dumazet wrote: > > On Fri, 2013-05-24 at 10:24 -0700, Jesse Gross wrote: > > > >> Does this have any impact on small packets? Those are usually the > >> common case (i.e. TCP SYN) and I think this is slightly less optimal > >> for those. > > > > No difference at all, small packets are copied anyway in skb->head > > Yes, but it makes the Open vSwitch code slightly worse - for example, > currently checksumming and copying are done in a single step but this > prevents that. Actually, I'm also curious about the test case that was > used for large packets and the full profile output since checksumming > and GSO aren't listed in the one that Thomas gave. > GSO is fully supported in nfnetlink, I see no reason why Open vSwitch would not allow that. > My guess is that there isn't a real different for small packets since > everything will be in the cache but it seems worth checking given that > this is optimizing a rare case at the expense of the common one. I really doubt checksumming a SYN/ACK packet is that a performance issue. Do you have performance numbers ? You could always provide a patch to restore this copy/checksum if it really gives a benefit, and if people still use NIC not doing this checksum.