Re: Memory-mapping TCP/UDP send/recv buffer?

From: Stanley Feng \(MSFT\) (sfeng_at_microsoft_dot_com)
Date: 03/30/04 

Date: Tue, 30 Mar 2004 12:32:15 -0800

Setting send buffer size to zero can give you zero copy on the send side.
Setting receive buffer size to zero can *not* give you zero copy on the
receive side. If data comes in and there is no pre-posted receive request,
TCP will have to buffer data in its receive window.

Article http://msdn.microsoft.com/msdnmag/issues/1000/Winsock/default.aspx,
section "Who managers the buffers" give you some brief ideas of what is
going on.

RE Memory mapping technique to achieve zero copy -

This has been widely deemed as a "software" solution to zero-copy along with
other techniques like "indicate-and-post", etc. They all have their
restrictions and limitations.

To obtain true zero copy, you will need hardware support. There are two
active tech. communities working on this -

www.rdmaconsortium.org

and the Rddp work group of IETF. 

-- 
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"Olaf van der Spek" <OvdSpek@LIACS.NL> wrote in message
news:%23m8kdtZFEHA.3424@tk2msftngp13.phx.gbl...
>
> "Louis Solomon [SteelBytes]" <louis@steelbytes.spam-is-bad.com> schreef in
> bericht news:O1C9$abEEHA.3568@tk2msftngp13.phx.gbl...
> > from memory, setting the socket buffer size to 0 has this affect.
> >
> But that has other effects as well and you still have to manage the
buffers
> at the application level.
>
> One reason memory-mapping looked nice is that you could map the buffer
> twice, so that you can always do a full sequential read in a circular
buffer
> without dealing with the wrapping yourself.
>
> > -- 
> > Louis Solomon
> > www.steelbytes.com
> >
> >
> > "Olaf van der Spek" <OvdSpek@LIACS.NL> wrote in message
> > news:u8qjPXaEEHA.3672@TK2MSFTNGP09.phx.gbl...
> > > Hi,
> > >
> > > I'm wondering, is it possible to somehow memory-map the TCP/UDP
> send/recv
> > > buffers so the kernel does not have to copy data from kernel- to
> > > user-space
> > > and the other way around?
> > >
> > > -- 
> > >
> > > Olaf van der Spek
> > > Almere, Holland
> > > http://xccu.sourceforge.net/
> > >
> > >
> >
> >
>
>

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