netdev - Re: [RFC 1/6] net: extend ubuf_info callback to ops structure

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Message-ID: <661d428c4c454_1073d2945f@willemb.c.googlers.com.notmuch>
Date: Mon, 15 Apr 2024 11:06:52 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Pavel Begunkov <asml.silence@...il.com>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 io-uring@...r.kernel.org, 
 netdev@...r.kernel.org
Cc: Jens Axboe <axboe@...nel.dk>, 
 "David S . Miller" <davem@...emloft.net>, 
 Jakub Kicinski <kuba@...nel.org>, 
 David Ahern <dsahern@...nel.org>, 
 Eric Dumazet <edumazet@...gle.com>
Subject: Re: [RFC 1/6] net: extend ubuf_info callback to ops structure

Pavel Begunkov wrote:
> On 4/14/24 18:07, Willem de Bruijn wrote:
> > Pavel Begunkov wrote:
> >> We'll need to associate additional callbacks with ubuf_info, introduce
> >> a structure holding ubuf_info callbacks. Apart from a more smarter
> >> io_uring notification management introduced in next patches, it can be
> >> used to generalise msg_zerocopy_put_abort() and also store
> >> ->sg_from_iter, which is currently passed in struct msghdr.
> > 
> > This adds an extra indirection for all other ubuf implementations.
> > Can that be avoided?
> 
> It could be fitted directly into ubuf_info, but that doesn't feel
> right. It should be hot, so does it even matter?

That depends on the workload (working set size)?

> On the bright side,
> with the patch I'll also ->sg_from_iter from msghdr into it, so it
> doesn't have to be in the generic path.

I don't follow this: is this suggested future work?

> 
> I think it's the right approach, but if you have a strong opinion
> I can fit it as a new field in ubuf_info.

If there is a significant cost, I suppose we could use
INDIRECT_CALL or go one step further and demultiplex
based on the new ops

    if (uarg->ops == &msg_zerocopy_ubuf_ops)
        msg_zerocopy_callback(..);