netdev - Re: [PATCH net-next] r8169: use netif_receive_skb

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Date:   Mon, 1 Apr 2019 18:31:39 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     David Miller <davem@...emloft.net>, <eric.dumazet@...il.com>
CC:     <hkallweit1@...il.com>, <nic_swsd@...ltek.com>,
        <netdev@...r.kernel.org>, <brouer@...hat.com>
Subject: Re: [PATCH net-next] r8169: use netif_receive_skb_list batching

On 01/04/2019 18:14, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Mon, 1 Apr 2019 02:17:12 -0700
>
>> This means no GRO at all
> I do not think that is true as the SKB list layer does queue up to
> GRO.
No, Eric is right; the current list layer bypasses GRO completely.

netif_receive_skb_list() ends up doing the same things netif_receive_skb()
would do on each SKB in the list, and that does not include GRO.
(For this reason the sfc driver only uses netif_receive_skb_list() for
non-TCP packets; TCP packets go to napi_gro_frags().)
I had a patch series to add napi_gro_receive_list() which would use the
SKB list layer to handle the packets GRO didn't coalesce ([1]) but the
performance tests I ran were inconclusive and it never got applied.

-Ed

[1]: https://marc.info/?l=linux-netdev&m=154221888012410&w=2