From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH] net: update the usage of CHECKSUM_UNNECESSARY Date: Thu, 10 May 2012 09:00:18 +0300 Message-ID: <20120510060018.GA23665@redhat.com> References: <20120319211241.11291.53271.stgit@localhost6.localdomain6> <20120508174831.GA27406@redhat.com> <1336501258.2749.3.camel@bwh-desktop.uk.solarflarecom.com> <20120509060308.GA13522@redhat.com> <1336608301.2499.12.camel@bwh-desktop.uk.solarflarecom.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Miller , Yi Zou , netdev@vger.kernel.org, devel@open-fcoe.org, jeffrey.t.kirsher@intel.com To: Ben Hutchings Return-path: Received: from mx1.redhat.com ([209.132.183.28]:42750 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752449Ab2EJGAg (ORCPT ); Thu, 10 May 2012 02:00:36 -0400 Content-Disposition: inline In-Reply-To: <1336608301.2499.12.camel@bwh-desktop.uk.solarflarecom.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, May 10, 2012 at 01:05:01AM +0100, Ben Hutchings wrote: > On Wed, 2012-05-09 at 09:03 +0300, Michael S. Tsirkin wrote: > > On Tue, May 08, 2012 at 07:20:58PM +0100, Ben Hutchings wrote: > > > On Tue, 2012-05-08 at 20:48 +0300, Michael S. Tsirkin wrote: > > > > On Mon, Mar 19, 2012 at 02:12:41PM -0700, Yi Zou wrote: > > > > > As suggested by Ben, this adds the clarification on the usage of > > > > > CHECKSUM_UNNECESSARY on the outgoing patch. Also add the usage > > > > > description of NETIF_F_FCOE_CRC and CHECKSUM_UNNECESSARY > > > > > for the kernel FCoE protocol driver. > > > > > > > > > > This is a follow-up to the following: > > > > > http://patchwork.ozlabs.org/patch/147315/ > > > > > > > > > > Signed-off-by: Yi Zou > > > > > Cc: Ben Hutchings > > > > > Cc: Jeff Kirsher > > > > > Cc: www.Open-FCoE.org > > > > > --- > > > > > > > > > > include/linux/skbuff.h | 7 +++++++ > > > > > 1 files changed, 7 insertions(+), 0 deletions(-) > > > > > > > > > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h > > > > > index 8dc8257..a2b9953 100644 > > > > > --- a/include/linux/skbuff.h > > > > > +++ b/include/linux/skbuff.h > > > > > @@ -94,6 +94,13 @@ > > > > > * about CHECKSUM_UNNECESSARY. 8) > > > > > * NETIF_F_IPV6_CSUM about as dumb as the last one but does IPv6 instead. > > > > > * > > > > > + * UNNECESSARY: device will do per protocol specific csum. Protocol drivers > > > > > + * that do not want net to perform the checksum calculation should use > > > > > + * this flag in their outgoing skbs. > > > > > + * NETIF_F_FCOE_CRC this indicates the device can do FCoE FC CRC > > > > > + * offload. Correspondingly, the FCoE protocol driver > > > > > + * stack should use CHECKSUM_UNNECESSARY. > > > > > + * > > > > > * Any questions? No questions, good. --ANK > > > > > */ > > > > > > > > > > > > > So just to make sure I understand, you never get > > > > UNNECESSARY packets on tx unless you declared NETIF_F_FCOE_CRC? > > > > > > > > Maybe the comment says this somehow but could not figure it out. > > > > > > That's what should happen now. In future CHECKSUM_UNNECESSARY could be > > > used on output by other protocols which don't use TCP/IP-style > > > checksums, but always dependent on the output device supporting the > > > relevant offload feature. > > > > > > Ben. > > > > Isn't there another case: a device passes UNNECESSARY in on rx, > > and the skb is forwarded to another device? > > For example it is handled this way by tun, giving a nice > > performance boost for VMs, see 10a8d94a95742bb15b4e617ee9884bb4381362be > > Hmm... I thought UNNECESSARY was supposed to be replaced by NONE on > output, but I don't see where that would happen. Which would mean we > had an undocumented case here, and now we have ambiguity. :-( > > Ben. Ambiguity with FCoE? Why doesn't that use PARTIAL btw? Simply to avoid teaching net core about that protocol and NETIF_F_FCOE_CRC? > -- > Ben Hutchings, Staff Engineer, Solarflare > Not speaking for my employer; that's the marketing department's job. > They asked us to note that Solarflare product names are trademarked.