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

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Message-ID: <20201222172158.4b266ljlwtsyrvcj@bsd-mbp.dhcp.thefacebook.com>
Date:   Tue, 22 Dec 2020 09:21:58 -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 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 also prefer not to rename flags that some of us are familiar with,
> if it's not needed.

Ack.
--
Jonathan