netdev - Re: [PATCH v4 net-next 1/5] ethtool: Add support for configuring tx_push_buf

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Message-ID: <20230313120942.75599b8e@kernel.org>
Date:   Mon, 13 Mar 2023 12:09:42 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Gal Pressman <gal@...dia.com>
Cc:     Shay Agroskin <shayagr@...zon.com>,
        David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        "Woodhouse, David" <dwmw@...zon.com>,
        "Machulsky, Zorik" <zorik@...zon.com>,
        "Matushevsky, Alexander" <matua@...zon.com>,
        Saeed Bshara <saeedb@...zon.com>,
        "Wilson, Matt" <msw@...zon.com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        "Bshara, Nafea" <nafea@...zon.com>,
        "Belgazal, Netanel" <netanel@...zon.com>,
        "Saidi, Ali" <alisaidi@...zon.com>,
        "Herrenschmidt, Benjamin" <benh@...zon.com>,
        "Kiyanovski, Arthur" <akiyano@...zon.com>,
        "Dagan, Noam" <ndagan@...zon.com>,
        "Arinzon, David" <darinzon@...zon.com>,
        "Itzko, Shahar" <itzko@...zon.com>,
        "Abboud, Osama" <osamaabb@...zon.com>
Subject: Re: [PATCH v4 net-next 1/5] ethtool: Add support for configuring
 tx_push_buf_len

On Sun, 12 Mar 2023 14:41:39 +0200 Gal Pressman wrote:
> On 10/03/2023 8:53, Jakub Kicinski wrote:
> > On Thu, 9 Mar 2023 19:15:43 +0200 Gal Pressman wrote:  
> >> I know Jakub prefers the new parameter, but the description of this
> >> still sounds extremely similar to TX copybreak to me..
> >> TX copybreak was traditionally used to copy packets to preallocated DMA
> >> buffers, but this could be implemented as copying the packet to the
> >> (preallocated) WQE's inline part. That usually means DMA memory, but
> >> could also be device memory in this ENA LLQ case.
> >>
> >> Are we drawing a line that TX copybreak is the threshold for DMA memory
> >> and tx_push_buf_len is the threshold for device memory?  
> > 
> > Pretty much, yes. Not an amazing distinction but since TX copybreak can
> > already mean two different things (inline or DMA buf) I'd err on 
> > the side of not overloading it with another one.   
> 
> Can we document that please?

Shay, could you add a paragraph in the docs regarding copybreak in v5?