netdev - Re: [PATCH 01/12 v2 RFC] net: group skb_shinfo zerocopy related bits together.

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Message-ID: <CAF=yD-Ky9RSZUhEFxz2SPdq6CGS-kfbUZc29=AmtzY--3SjZmA@mail.gmail.com>
Date:   Tue, 22 Dec 2020 17:26:15 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jonathan Lemon <jonathan.lemon@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH 01/12 v2 RFC] net: group skb_shinfo zerocopy related bits together.

On Tue, Dec 22, 2020 at 12:22 PM Jonathan Lemon
<jonathan.lemon@...il.com> wrote:
>
> On Tue, Dec 22, 2020 at 09:43:15AM -0500, Willem de Bruijn wrote:
> > On Mon, Dec 21, 2020 at 7:09 PM Jonathan Lemon <jonathan.lemon@...il.com> wrote:
> > >
> > > From: Jonathan Lemon <bsd@...com>
> > >
> > > In preparation for expanded zerocopy (TX and RX), move
> > > the ZC related bits out of tx_flags into their own flag
> > > word.
> > >
> > > Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
> >
> > I think it's better to expand tx_flags to a u16 and add the two new
> > flags that you need.
>
> Okay, but in that case, tx_flags is now wrong, since some of these flags
> will also be checked on the rx path.
>
>
> > That allows the additional 7 bits to be used for arbitrary flags, not
> > stranding 8 bits exactly only for zerocopy features.
> >
> > Moving around a few u8's in the same cacheline won't be a problem.
>
> How about rearranging them to form 16 bits, and just calling it 'flags'?

I thought that would be a good idea, but tx_flags is used in a lot
more places than I expected. That will be a lot of renaming. Let's
just either keep the name or add a new field.