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

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Message-ID: <8b0aba42-627a-f5f5-a9ec-237b69b3b03f@nvidia.com>
Date:   Sun, 13 Nov 2022 11:48:37 +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 11/11/2022 19:07, Jakub Kicinski wrote:
> On Wed,  9 Nov 2022 19:02:47 +0100 Daniele Palmas wrote:
>> Add the following ethtool tx aggregation parameters:
>>
>> ETHTOOL_A_COALESCE_TX_MAX_AGGR_SIZE
>> Maximum size of an aggregated block of frames in tx.
> perhaps s/size/bytes/ ? Or just mention bytes in the doc? I think it's
> the first argument in coalescing expressed in bytes, so to avoid
> confusion we should state that clearly.
>
>> ETHTOOL_A_COALESCE_TX_MAX_AGGR_FRAMES
>> Maximum number of frames that can be aggregated into a block.
>>
>> ETHTOOL_A_COALESCE_TX_USECS_AGGR_TIME
>> Time in usecs after the first packet arrival in an aggregated
>> block for the block to be sent.
> Can we add this info to the ethtool-netlink.rst doc?
>
> Can we also add a couple of sentences describing what aggregation is?
> Something about copying the packets into a contiguous buffer to submit
> as one large IO operation, usually found on USB adapters?
>
> People with very different device needs will read this and may pattern
> match the parameters to something completely different like just
> delaying ringing the doorbell. So even if things seem obvious they are
> worth documenting.

Seems like I am these people, I was under the impression this is kind of
a threshold for xmit more or something?
What is this contiguous buffer? Isn't this the same as TX copybreak? TX
copybreak for multiple packets?