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

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Message-ID: <20201222224011.tk6iykdcg4d5f4yb@bsd-mbp.dhcp.thefacebook.com>
Date:   Tue, 22 Dec 2020 14:40:11 -0800
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...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 05:26:15PM -0500, Willem de Bruijn wrote:
> 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.

Hmm, which?  I went with "add new field" = zc_flags.  I can rename this
to something else if that's too specific.  Suggestions?
-- 
Jonathan   "naming is hard!"