netdev - Re: [PATCH net-next] sctp: define sctp_packet_gso

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Message-ID: <20180614004643.GA12409@neilslaptop.think-freely.org>
Date:   Wed, 13 Jun 2018 20:46:43 -0400
From:   Neil Horman <nhorman@...driver.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        davem@...emloft.net, eric.dumazet@...il.com
Subject: Re: [PATCH net-next] sctp: define sctp_packet_gso_append to build
 GSO frames

On Thu, Jun 14, 2018 at 07:37:02AM +0800, Xin Long wrote:
> Now sctp GSO uses skb_gro_receive() to append the data into head
> skb frag_list. However it actually only needs very few code from
> skb_gro_receive(). Besides, NAPI_GRO_CB has to be set while most
> of its members are not needed here.
> 
> This patch is to add sctp_packet_gso_append() to build GSO frames
> instead of skb_gro_receive(), and it would avoid many unnecessary
> checks and make the code clearer.
> 
> Note that sctp will use page frags instead of frag_list to build
> GSO frames in another patch. But it may take time, as sctp's GSO
> frames may have different size. skb_segment() can only split it
> into the frags with the same size, which would break the border
> of sctp chunks.
> 
> Signed-off-by: Xin Long <lucien.xin@...il.com>
Do you have any performance numbers to compare with and without this patch?
Adding a function like this implies that any fixes that go into skb_gro_receive
now need to be evaluated for this function too, which means theres an implied
overhead in maintaining it.  If we're signing up for that, I'd like to know that
theres a significant performance benefit.

Neil