linux-kernel - Re: [PATCH v3 1/1] gro: decrease size of CB

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Date:   Mon, 26 Jun 2023 11:55:47 +0300
From:   Gal Pressman <gal@...dia.com>
To:     Richard Gobert <richardbgobert@...il.com>, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        aleksander.lobakin@...el.com, lixiaoyan@...gle.com,
        lucien.xin@...il.com, alexanderduyck@...com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] gro: decrease size of CB

On 01/06/2023 19:14, Richard Gobert wrote:
> The GRO control block (NAPI_GRO_CB) is currently at its maximum size.
> This commit reduces its size by putting two groups of fields that are
> used only at different times into a union.
> 
> Specifically, the fields frag0 and frag0_len are the fields that make up
> the frag0 optimisation mechanism, which is used during the initial
> parsing of the SKB.
> 
> The fields last and age are used after the initial parsing, while the
> SKB is stored in the GRO list, waiting for other packets to arrive.
> 
> There was one location in dev_gro_receive that modified the frag0 fields
> after setting last and age. I changed this accordingly without altering
> the code behaviour.
> 
> Signed-off-by: Richard Gobert <richardbgobert@...il.com>

Hello Richard,

I believe this commit broke gro over udp tunnels.
I'm running iperf tcp traffic over geneve interfaces and the bandwidth
is pretty much zero.

Turning off gro on the receiving side (or reverting this commit)
resolves the issue.