From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Ricardo Leitner Subject: Re: [PATCH 3/3] docs: segmentation-offloads.txt: add SCTP info Date: Wed, 14 Feb 2018 11:00:43 -0200 Message-ID: <20180214130043.GA4625@localhost.localdomain> References: <20180214070533.28377-1-dja@axtens.net> <20180214070533.28377-4-dja@axtens.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, linux-sctp@vger.kernel.org To: Daniel Axtens Return-path: Received: from mail-qk0-f195.google.com ([209.85.220.195]:35726 "EHLO mail-qk0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750925AbeBNNAs (ORCPT ); Wed, 14 Feb 2018 08:00:48 -0500 Content-Disposition: inline In-Reply-To: <20180214070533.28377-4-dja@axtens.net> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Feb 14, 2018 at 06:05:33PM +1100, Daniel Axtens wrote: > Most of this is extracted from 90017accff61 ("sctp: Add GSO support"), > with some extra text about GSO_BY_FRAGS and the need to check for it. > > Cc: Marcelo Ricardo Leitner > Signed-off-by: Daniel Axtens Acked-by: Marcelo Ricardo Leitner > --- > Documentation/networking/segmentation-offloads.txt | 26 ++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > diff --git a/Documentation/networking/segmentation-offloads.txt b/Documentation/networking/segmentation-offloads.txt > index b247471a183c..d47480b61ac6 100644 > --- a/Documentation/networking/segmentation-offloads.txt > +++ b/Documentation/networking/segmentation-offloads.txt > @@ -13,6 +13,7 @@ The following technologies are described: > * Generic Segmentation Offload - GSO > * Generic Receive Offload - GRO > * Partial Generic Segmentation Offload - GSO_PARTIAL > + * SCTP accelleration with GSO - GSO_BY_FRAGS > > TCP Segmentation Offload > ======================== > @@ -132,3 +133,28 @@ values for if the header was simply duplicated. The one exception to this > is the outer IPv4 ID field. It is up to the device drivers to guarantee > that the IPv4 ID field is incremented in the case that a given header does > not have the DF bit set. > + > +SCTP accelleration with GSO > +=========================== > + > +SCTP - despite the lack of hardware support - can still take advantage of > +GSO to pass one large packet through the network stack, rather than > +multiple small packets. > + > +This requires a different approach to other offloads, as SCTP packets > +cannot be just segmented to (P)MTU. Rather, the chunks must be contained in > +IP segments, padding respected. So unlike regular GSO, SCTP can't just > +generate a big skb, set gso_size to the fragmentation point and deliver it > +to IP layer. > + > +Instead, the SCTP protocol layer builds an skb with the segments correctly > +padded and stored as chained skbs, and skb_segment() splits based on those. > +To signal this, gso_size is set to the special value GSO_BY_FRAGS. > + > +Therefore, any code in the core networking stack must be aware of the > +possibility that gso_size will be GSO_BY_FRAGS and handle that case > +appropriately. (For size checks, the skb_gso_validate_*_len family of > +helpers do this automatically.) > + > +This also affects drivers with the NETIF_F_FRAGLIST & NETIF_F_GSO_SCTP bits > +set. Note also that NETIF_F_GSO_SCTP is included in NETIF_F_GSO_SOFTWARE. > -- > 2.14.1 >