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Message-ID: <e4bbe997-326f-b6cf-b6d6-f0a24f5aef39@intel.com> Date: Thu, 5 Oct 2023 18:58:33 +0200 From: Alexander Lobakin <aleksander.lobakin@...el.com> To: Jakub Kicinski <kuba@...nel.org> CC: Larysa Zaremba <larysa.zaremba@...el.com>, <bpf@...r.kernel.org>, <ast@...nel.org>, <daniel@...earbox.net>, <andrii@...nel.org>, <martin.lau@...ux.dev>, <song@...nel.org>, <yhs@...com>, <john.fastabend@...il.com>, <kpsingh@...nel.org>, <sdf@...gle.com>, <haoluo@...gle.com>, <jolsa@...nel.org>, David Ahern <dsahern@...il.com>, Willem de Bruijn <willemb@...gle.com>, Jesper Dangaard Brouer <brouer@...hat.com>, Anatoly Burakov <anatoly.burakov@...el.com>, "Alexander Lobakin" <alexandr.lobakin@...el.com>, Magnus Karlsson <magnus.karlsson@...il.com>, Maryam Tahhan <mtahhan@...hat.com>, <xdp-hints@...-project.net>, <netdev@...r.kernel.org>, Willem de Bruijn <willemdebruijn.kernel@...il.com>, Alexei Starovoitov <alexei.starovoitov@...il.com>, Simon Horman <simon.horman@...igine.com>, Tariq Toukan <tariqt@...lanox.com>, Saeed Mahameed <saeedm@...lanox.com>, Maciej Fijalkowski <maciej.fijalkowski@...el.com> Subject: Re: [xdp-hints] Re: [RFC bpf-next v2 09/24] xdp: Add VLAN tag hint From: Jakub Kicinski <kuba@...nel.org> Date: Wed, 4 Oct 2023 11:08:50 -0700 > On Tue, 3 Oct 2023 15:09:39 +0200 Alexander Lobakin wrote: >>> Sorry for a random chime-in but was there any discussion about >>> the validity of VLAN stripping as an offload? >>> >>> I always thought this is a legacy "Windows" thing which allowed >>> Windows drivers to operate on VLAN-tagged networks even before >>> the OS itself understood VLANs... Do people actually care about >>> having it enabled? >> >> On MIPS routers, I actually have some perf gains from having it enabled. >> So they do, I'd say. Mediatek even has DSA tag stripping. Both save you >> some skb->data push-pulls, csum corrections when CHECKSUM_COMPLETE, skb >> unsharing in some cases, reduce L3/L4 headers cacheline spanning etc. > > No unsharing - you can still strip it in the driver. Nobody manually strips VLAN tags in the drivers. You either have HW stripping or pass VLAN-tagged skb to the stack, so that skb_vlan_untag() takes care of it. > Do you really think that for XDP kfunc call will be cheaper? Wait, you initially asked: * discussion about the validity of VLAN stripping as an offload? * Do people actually care about having it enabled? I did read this as "do we still need HW VLAN stripping in general?", not only for XDP. So I replied for "in general" -- yes. Forcefully disabling stripping when XDP is active is obscure IMO, let the user decide. Thanks, Olek
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