From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCHv1 net-next] xen-netback: remove unconditional pull_skb_tail in guest Tx path Date: Wed, 5 Nov 2014 09:53:05 +0000 Message-ID: <1415181185.11486.65.camel@citrix.com> References: <1415035431-27485-1-git-send-email-david.vrabel@citrix.com> <20141104.164113.2265592775058059992.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: , , , , To: David Miller Return-path: Received: from smtp.citrix.com ([66.165.176.89]:50679 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751396AbaKEJxI (ORCPT ); Wed, 5 Nov 2014 04:53:08 -0500 In-Reply-To: <20141104.164113.2265592775058059992.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 2014-11-04 at 16:41 -0500, David Miller wrote: > From: David Vrabel > Date: Mon, 3 Nov 2014 17:23:51 +0000 > > > From: Malcolm Crossley > > > > Unconditionally pulling 128 bytes into the linear buffer is not > > required. Netback has already grant copied up-to 128 bytes from the > > first slot of a packet into the linear buffer. The first slot normally > > contain all the IPv4/IPv6 and TCP/UDP headers. > > > > The unconditional pull would often copy frag data unnecessarily. This > > is a performance problem when running on a version of Xen where grant > > unmap avoids TLB flushes for pages which are not accessed. TLB > > flushes can now be avoided for > 99% of unmaps (it was 0% before). > > > > Grant unmap TLB flush avoidance will be available in a future version > > of Xen (probably 4.6). > > > > Signed-off-by: Malcolm Crossley > > Signed-off-by: David Vrabel > > Now that this has been discussed a bit, it is possible to get an ack or two? I'd like to see the commit message expanded to explain why this isn't introducing a (security) bug by not pulling enough stuff into the header (IOW the conclusion of the discussion). Ian.