netdev - Re: all syscalls initially taking 4usec on a P4? Re: nonblocking UDPv4 recvfrom() taking 4usec @ 3GHz?

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Date:	Tue, 20 Feb 2007 19:41:25 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	bert hubert <bert.hubert@...herlabs.nl>
Cc:	Andi Kleen <andi@...stfloor.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: all syscalls initially taking 4usec on a P4? Re: nonblocking UDPv4 recvfrom() taking 4usec @ 3GHz?

On Tue, Feb 20, 2007 at 05:27:14PM +0100, bert hubert (bert.hubert@...herlabs.nl) wrote:
> I've done so, with some interesting results. Source on
> http://ds9a.nl/tmp/recvtimings.c - be careful to adjust the '3000' divider
> to your CPU frequency if you care about absolute numbers!
> 
> These are two groups, each consisting of 10 consecutive nonblocking UDP
> recvfroms, with 10 packets preloaded. Reported is the number of microseconds
> per recvfrom call which yielded a packet:
> 
> $ ./recvtimings
> 4.142333

It can be recvfrom only problem - syscall overhead on my p4 (core duo,
debian testing) is bout 300 usec - to test I ran 
read('dev/zero', &data, 0)
in a loop.

Could you try to hack recvfrom() for your socket to always copy some
empty buffer and check the results without waiting for packet?

If you are not hurry I can test it myself tomorrow.

-- 
	Evgeniy Polyakov
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