linux-kernel - 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 14:40:40 -0500
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	bert hubert <bert.hubert@...herlabs.nl>,
	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 08:33:20PM +0100, bert hubert wrote:
> I'm investigating this further for other system calls. It might be that my
> measurements are off, but it appears even a slight delay between calls
> incurs a large penalty.

Make sure your system is idle.  Userspace bloat means that *lots* of idle 
activity occurs in between timer ticks on recent distributions -- all those 
widgets polling the hardware to see if something changed or needs updating 
do a lot of damage to the caches.  Try comparing a run under init=/bin/bash 
with one while logged in to a desktop environment to see just how painful it 
is.

		-ben
-- 
"Time is of no importance, Mr. President, only life is important."
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