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

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Message-ID: <20070220204505.GB8800@outpost.ds9a.nl>
Date:	Tue, 20 Feb 2007 21:45:05 +0100
From:	bert hubert <bert.hubert@...herlabs.nl>
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	Evgeniy Polyakov <johnpol@....mipt.ru>,
	Josef Sipek <jsipek@....cs.sunysb.edu>,
	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 02:40:40PM -0500, Benjamin LaHaise wrote:

> Make sure your system is idle.  Userspace bloat means that *lots* of idle 
> activity occurs in between timer ticks on recent distributions -- all those 

You hit the nail on the head. I had previously measured with X shut down,
but the effect didn't disappear.

With init=/bin/bash, recvfrom suddenly takes from 900nsec to 1.3usec, with
only slight correlation between inter-call delay and cycles spent.

I'm investigating this further as it appears this has a real life effect on
my P4 - a drastic one!

processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 4
model name      : Intel(R) Pentium(R) 4 CPU 3.00GHz
stepping        : 1
cpu MHz         : 3000.131
cache size      : 1024 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 5
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx
constant_tsc pni monitor ds_cpl cid xtpr
bogomips        : 6003.91
clflush size    : 64

Thanks for your help!

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