Re: [PATCH v1 2/3] io: Add zerocopy and errqueue

[Peter Xu]

On Wed, Sep 08, 2021 at 05:25:50PM -0300, Leonardo Bras Soares Passos wrote:
> On Tue, Sep 7, 2021 at 8:06 AM Dr. David Alan Gilbert
> <dgilbert@redhat.com> wrote:
> > > Possibly, yes. This really need David G's input since he understands
> > > the code in way more detail than me.
> >
> > Hmm I'm not entirely sure why we have the sync after each iteration;
> > the case I can think of is if we're doing async sending, we could have
> > two versions of the same page in flight (one from each iteration) -
> > you'd want those to get there in the right order.
> >
> > Dave
> 
> Well, that's the thing: as we don't copy the buffer in MSG_ZEROCOPY,  we will 
> in
> fact have the same page in flight twice, instead of two versions,
> given the buffer is
> sent as it is during transmission.

That's an interesting point, which looks even valid... :)

There can still be two versions depending on when the page is read and feed to
the NICs as the page can be changing during the window, but as long as the
latter sent page always lands later than the former page on dest node then it
looks ok.

-- 
Peter Xu