Date: Wed, 30 Jan 2008 12:15:59 +0100
From: Luotao Fu <l.fu@pengutronix.de>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Wolfgang Grandegger <wg@grandegger.com>, Luotao Fu <l.fu@pengutronix.de>,
       Steven Rostedt <rostedt@goodmis.org>,
       LKML <linux-kernel@vger.kernel.org>,
       RT <linux-rt-users@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>
Subject: Re: 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc - RCU
	issue?
Message-ID: <20080130111559.GC20089@pengutronix.de>
Mail-Followup-To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Wolfgang Grandegger <wg@grandegger.com>,
	Luotao Fu <l.fu@pengutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	LKML <linux-kernel@vger.kernel.org>,
	RT <linux-rt-users@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
	Thomas Gleixner <tglx@linutronix.de>
References: <47976D06.1010900@grandegger.com> <479DF0A1.3000906@pengutronix.de> <479DF711.5090406@grandegger.com> <479F186A.4020004@pengutronix.de> <479F2C3C.1020203@grandegger.com> <20080130010716.GB16069@linux.vnet.ibm.com> <47A032E9.4080105@grandegger.com> <20080130102255.GA24890@linux.vnet.ibm.com> <47A0552D.20605@grandegger.com> <20080130105715.GE24890@linux.vnet.ibm.com>
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Hi,

On Wed, Jan 30, 2008 at 02:57:16AM -0800, Paul E. McKenney wrote:
=2E.....
> > 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.
>=20
> I have to ask...
>=20
> Did you see large latencies when -not- running on NFS?
>=20

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
--=20
   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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