netdev - Re: [PATCH net-next v6 3/9] bnxt_en: add support for tcp-data-split ethtool command

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Message-ID: <Z2R1GFOg1hapdfl-@JRM7P7Q02P.dhcp.broadcom.net>
Date: Thu, 19 Dec 2024 14:33:44 -0500
From: Andy Gospodarek <andrew.gospodarek@...adcom.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Taehee Yoo <ap420073@...il.com>, davem@...emloft.net, pabeni@...hat.com,
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Subject: Re: [PATCH net-next v6 3/9] bnxt_en: add support for tcp-data-split
 ethtool command

On Thu, Dec 19, 2024 at 07:25:19AM -0800, Jakub Kicinski wrote:
> On Fri, 20 Dec 2024 00:14:01 +0900 Taehee Yoo wrote:
> > > > The bnxt_en disallows setting up both single and multi buffer XDP, but core
> > > > checks only single buffer XDP. So, if multi buffer XDP is attaching to
> > > > the bnxt_en driver when HDS is enabled, the core can't filter it.  
> > >
> > > Hm. Did you find this in the code, or did Broadcom folks suggest it?
> > > AFAICT bnxt supports multi-buf XDP. Is there something in the code
> > > that special-cases aggregation but doesn't work for pure HDS?  
> > 
> > There were some comments about HDS with XDP in the following thread.
> > https://lore.kernel.org/netdev/20241022162359.2713094-1-ap420073@gmail.com/T/
> > I may misunderstand reviews from Broadcom folks.
> 
> I see it now in bnxt_set_rx_skb_mode. I guess with high MTU
> the device splits in some "dumb" way, at a fixed offset..
> You're right, we have to keep the check in the driver, 
> at least for now.

The mutlti-buffer implementation followed what was done at the time in
other drivers.  Is the 'dumb way' you mention this check?

 4717                 if (dev->mtu > BNXT_MAX_PAGE_MODE_MTU) {
 4718                         bp->flags |= BNXT_FLAG_JUMBO;
 4719                         bp->rx_skb_func = bnxt_rx_multi_page_skb;
 4720                 } else {
 4721                         bp->flags |= BNXT_FLAG_NO_AGG_RINGS;
 4722                         bp->rx_skb_func = bnxt_rx_page_skb;
 4723                 }