Support for zero copy sockets

[Alan Cox]

The send path used an ad hoc copy-on-write mechanism, i.e., it was not the
mechanism used by fork, etc.  This mechanism was broken (and as I'll argue
in a few sentences not worth fixing).  The receive path used page flipping
and required support from the NIC.  Neither copy-on-write nor page flipping
are viable approaches on today's multicore machines because their
implementation entails interprocessor TLB shootdowns.  Let them rest in
peace.




On Mon, Aug 11, 2014 at 1:04 PM, Adrian Chadd <adrian at freebsd.org> wrote:

> On 11 August 2014 01:26, Victor Balada Diaz <victor at bsdes.net> wrote:
> > On Mon, Aug 04, 2014 at 10:00:16AM -0700, Sushanth Rai via
> freebsd-hackers wrote:
> >> Hello,
> >>
> >> FreeBSD 10 release sources doesn't seem to have zero copy socket code
> anymore. What's is alternative to do zero_copy ?
> >>
> >> Thanks,
> >> Sushanth
> >
> > You need to use sendfile(2). In the man page is stated that the
> implementation in FreeBSD
> > is zero copy.
> >
> > You can also check:
> >
> > http://svnweb.freebsd.org/base?view=revision&revision=255608
> >
>
> I'd like to reintroduce a zero copy socket IO method for at least
> write that doesn't rely on sendfile.
>
> The zero-copy socket page flipping thing was interesting because IIRC
> tried to work for both sending and receiving socket data. Doing that
> via an API would be nicer.
>
> So, if people have an idea for how it could be done / what the API
> looks like then I'm all ears.
>
>
>
> -a
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