netdev - RE: zero copy for relay server

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Date:	Mon, 28 Mar 2011 20:34:17 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Viral Mehta <Viral.Mehta@...infotech.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: zero copy for relay server

Le lundi 28 mars 2011 à 23:48 +0530, Viral Mehta a écrit :

> Still, these are two system calls.

Yes. Is it a problem ? What kind ?

> In addition to this, many things to handle,
> 1. if the incoming_fd is blocking, then it will block till 64K data read. Why so ?

I dont think so. Try it, like read() of recv().

> 2. I believe underlying PIPE that we are using will also have some size limit
>     (like in user space 4K or 64K, not sure)

What kind of socket is able to deliver more than 64K frames ?

> 
> So, all in all
> Why cant we have just one system call which really transfers "length"
> bytes of data form one socket to another ? Recv "length" bytes of data
> from socket A and send to socket B.
> 
> I wanted to understand if there are any limitations or concerns that we still do
> not have any such system call .... ?
> 

The answer is : Once you try to implement this, you'll discover it'll be
splice() based, using pipe as a buffer between the sockets.

sendfile() is based on top of splice(), but it's faster to use splice().



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