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

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Message-ID: <CACKFLikUM=Vt1EeYEs_-amCmahak3nQPSbwz_v4T1pB=UShQ3w@mail.gmail.com>
Date: Thu, 19 Dec 2024 15:41:17 -0800
From: Michael Chan <michael.chan@...adcom.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Andy Gospodarek <andrew.gospodarek@...adcom.com>, Taehee Yoo <ap420073@...il.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 12:18 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 19 Dec 2024 14:33:44 -0500 Andy Gospodarek wrote:
> > > 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                 }
>
> Yes, that and my interpretation of the previous discussion let me to
> believe that the BNXT_FLAG_JUMBO does not enable header-data split.
> And speculating further I thought that perhaps the buffer split with
> jumbo > 4k is to fill first buffer completely, header+however much
> data fits.
>
> I could have misread the previous conversation (perhaps Michael meant
> XDP SB / PAGE_MODE when he was referring to XDP limitations?)

To clarify, my review comment applied to XDP SB and MB modes.  Andy's
MB implementation from 2022 disables HWGRO/LRO and HDS in XDP MB mode.
My comment was to preserve this implementation.

>
> Or maybe the HDS does happen with XDP MB but there is another
> limitation in the code?

HW doesn't know whether we're in XDP mode or not and can definitely do
HDS.  But again, HDS is disabled currently in any XDP mode.  Andy will
respond to discuss this further.  Long term, we may be able to enable
HDS in XDP MB mode, but for now I think we should disable it just to
keep it unchanged.

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