From mboxrd@z Thu Jan  1 00:00:00 1970
From: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Subject: Re: all syscalls initially taking 4usec on a P4? Re: nonblocking UDPv4 recvfrom() taking 4usec @ 3GHz?
Date: Tue, 20 Feb 2007 21:48:59 +0300
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Cc: bert hubert <bert.hubert@netherlabs.nl>,
	Andi Kleen <andi@firstfloor.org>, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
To: Josef Sipek <jsipek@fsl.cs.sunysb.edu>
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On Tue, Feb 20, 2007 at 01:42:42PM -0500, Josef Sipek (jsipek@fsl.cs.sunysb.edu) wrote:
> A better thing would be to use getuid - it turns into just a return with a
> memory dereference). I ran it on my 3.06GHz P4 (HT, but only UP kernel),
> PREEMPT, HZ=1000...
> 
> 3.290196 0.470588 0.402614 0.396078 0.393464 0.396078 0.386928 0.386928 0.386928 0.386928
> 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928
> 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928
> 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928 0.386928

I got following.

delta for syscall: 9112 cycles = 2.977778 us
delta for syscall: 1224 cycles = 0.400000 us
delta for syscall: 1071 cycles = 0.350000 us
delta for syscall: 1054 cycles = 0.344444 us
delta for syscall: 1054 cycles = 0.344444 us

Likely first overhead related to cache population or gamma-ray radiation.
If it happens only one (it does in my test), then everything is ok I
think. Bert, how frequently you get that long recvfrom()?

-- 
	Evgeniy Polyakov