netdev - Re: [PATCH net-next 1/3] ethtool: add tx aggregation parameters

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Date:   Tue, 15 Nov 2022 12:59:47 +0200
From:   Gal Pressman <gal@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>, Daniele Palmas <dnlplm@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Subash Abhinov Kasiviswanathan <quic_subashab@...cinc.com>,
        Sean Tranchetti <quic_stranche@...cinc.com>,
        Jonathan Corbet <corbet@....net>,
        Bjørn Mork <bjorn@...k.no>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next 1/3] ethtool: add tx aggregation parameters

On 15/11/2022 02:42, Jakub Kicinski wrote:
> On Mon, 14 Nov 2022 11:06:19 +0100 Daniele Palmas wrote:
>>> Isn't this the same as TX copybreak? TX
>>> copybreak for multiple packets?  
>> I tried looking at how tx copybreak works to understand your comment,
>> but I could not find any useful document. Probably my fault, but can
>> you please point me to something I can read?
> FWIW it's not exactly copy break, as it applies to all packets.
> But there is indeed an extra copy.
>
> Daniele's explanation is pretty solid, USB devices very often try 
> to pack multiple packets into a single URB for better perf. IIUC Linux
> drivers implement the feature on the Rx side, but fall short of doing
> the same on the Tx side, because there's no API to control it.
>
> I've seen the same thing in the WiFi USB devices I worked on in my
> youth :)

Thanks for the explanation.
How would this apply to a pci netdev driver?