linux-kernel - Re: rcu self-detected stall messages on OMAP3, 4 boards

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Message-ID: <20120921220302.GF2454@linux.vnet.ibm.com>
Date:	Fri, 21 Sep 2012 15:03:03 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Tony Lindgren <tony@...mide.com>
Cc:	Paul Walmsley <paul@...an.com>, "Bruce, Becky" <bbruce@...com>,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	"<linux-kernel@...r.kernel.org>" <linux-kernel@...r.kernel.org>,
	"<linux-omap@...r.kernel.org>" <linux-omap@...r.kernel.org>,
	"<linux-arm-kernel@...ts.infradead.org>" 
	<linux-arm-kernel@...ts.infradead.org>,
	"Hilman, Kevin" <khilman@...com>,
	"Shilimkar, Santosh" <santosh.shilimkar@...com>,
	"Hunter, Jon" <jon-hunter@...com>,
	"<snijsure@...d-net.com>" <snijsure@...d-net.com>,
	fweisbec@...il.com
Subject: Re: rcu self-detected stall messages on OMAP3, 4 boards

On Fri, Sep 21, 2012 at 01:31:49PM -0700, Tony Lindgren wrote:
> * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> [120921 12:58]:
> > 
> > Just to make sure I understand the combinations:
> > 
> > o	All stalls have happened when running a minimal userspace.
> > o	CONFIG_NO_HZ=n suppresses the stalls.
> > o	CONFIG_RCU_FAST_NO_HZ (which depends on CONFIG_NO_HZ=y) has
> > 	no observable effect on the stalls.
> 
> The reason why you may need minimal userspace is to cut down
> the number of timers waking up the system with NO_HZ.
> Booting with init=/bin/sh might also do the trick for that.

Good point!  This does make for a very quiet system, but does not
reproduce the problem under kvm, even after waiting for four minutes.
I will leave it for more time, but it looks like I really might need to
ask Linaro for remote access to a Panda.

							Thanx, Paul

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