linux-kernel - Re: Unix sockets via TCP on localhost: is TCP slower?

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Date:	Fri, 14 Nov 2008 10:06:57 +0100
From:	"Olaf van der Spek" <olafvdspek@...il.com>
To:	"Eric Dumazet" <dada1@...mosbay.com>
Cc:	"J.R. Mauro" <jrm8005@...il.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: Unix sockets via TCP on localhost: is TCP slower?

On Fri, Nov 14, 2008 at 9:54 AM, Eric Dumazet <dada1@...mosbay.com> wrote:
>> I expected the kernel to copy data directly from user-space of the
>> sending process to a kernel buffer of the receiving process, much like
>> UNIX sockets.
>>
>
> localhost uses a standard network device, and whole network stack
> is used, no 'special kludges'. You can add iptables rules, you
> can do trafic shaping, trafic sniffing (tcpdump), limiting
> memory used by all sockets (controlling memory pressure on the
> machine)
>
> Doing what you suggest would slow down AF_INET stack.

Why?

> You probably can expect AF_UNIX to be faster, since this one is really
> special and use shortcuts.
>
> Then, you probably can use shared memory instead of AF_UNIX, or
> pipes (and splice()), or ...
>
> Then you probably can use threads and do zero-copy ;)

Hmm, I'd like to avoid running my web server inside of my database
server process. ;)
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