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 23:17:20 +0100
From:	bert hubert <bert.hubert@...herlabs.nl>
To:	Rick Jones <rick.jones2@...com>
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 02:02:00PM -0800, Rick Jones wrote:

> The slope appears to be flattening-out the farther out to the right it 
> goes.  Perhaps that is the length of time it takes to take all the 
> requisite cache misses.

The rate of flattening out appears to correlate with the number of processes
running, even though the system is otherwise >99.5% idle during my
measurements.

With only 'gdm' running, things flatten out slowly, iow, it takes longer
delays to see recvfrom slow down. With only 1 process running (init=bash),
the graph is nearly flat.

>From this, it is probable that even an idle GNOME desktop (Ubunty Edgy Eft)
is under fierce cache pressure, enough to blow away my meagre 1MB in a
matter of milliseconds.

I'm trying to figure out which processes have the most impact, I had already
killed anything non-essential. But that still leaves 140 pids.

	Bert

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