linux-kernel - Re: 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc

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Date:	Wed, 30 Jan 2008 12:15:59 +0100
From:	Luotao Fu <l.fu@...gutronix.de>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Wolfgang Grandegger <wg@...ndegger.com>,
	Luotao Fu <l.fu@...gutronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc - RCU
	issue?

Hi,

On Wed, Jan 30, 2008 at 02:57:16AM -0800, Paul E. McKenney wrote:
......
> > Yes, I used "$ cyclictest -n -t1 -p80 -i1000" to measure the latency. So
> > far, I have not done other tests. Any recommendation?
> > As no-rt load I used "while ls; do ls /bin; done" in one telnet window
> > and "while ./hackbench 10; do ./calibrator 400 32M cali; sleep 30; done"
> > in another. But already "while ls; do ls /bin; done" is enough to
> > trigger the high latencies quickly. Note also, that I work on a root
> > files-ystem mounted via NFS resulting in a lot of network traffic and
> > utilization.
> 
> I have to ask...
> 
> Did you see large latencies when -not- running on NFS?
> 

I cannot speak for Wolfgang but I myself did not get extraordinary high
latencies running tests on system booted from flash. Neither I could produce
high latencies on nfs booted system. If my non-rt workload doesn't do heavy
filesystem/network accesses. i.E. running only hackbench. Hence we were
wondering if the problem is caused by rcu's in network layer or nfs
implementation.

regards
Luotao Fu
-- 
   Dipl.-Ing. Luotao Fu | Phone: +49-5121-206917-3
Pengutronix - Linux Solutions for Science and Industry
Entwicklungszentrum Nord     http://www.pengutronix.de


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