linux-kernel - Re: [2.6.28-rc5] RCU detected CPU 0 stall (t=4294893165/750 jiffies)

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Message-ID: <20081121173800.GS24427@vanheusden.com>
Date:	Fri, 21 Nov 2008 18:38:00 +0100
From:	Folkert van Heusden <folkert@...heusden.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org
Subject: Re: [2.6.28-rc5] RCU detected CPU 0 stall (t=4294893165/750
	jiffies)

> > > > I'm afraid there's no script for that: it happens during boot.
> > > This is a HZ=250 machine, correct?  If so, please try the following
> > > patch (already in -tip), which helps suppress boot-time false positives.
> > That's correct, 250Hz.
> > > -#define RCU_SECONDS_TILL_STALL_CHECK	( 3 * HZ) /* for rcp->jiffies_stall */
> > > +#define RCU_SECONDS_TILL_STALL_CHECK	(10 * HZ) /* for rcp->jiffies_stall */
> > Isn't it better to let the define depend on the value of CONFIG_HZ?
> > E.g.
> The stalls occur when CPUs spin in the kernel with preemption (or irqs
> or whatever) disabled.  So while I suppose that there is some
> possibility that such a spin might be a function of HZ, I have never
> seen this happen.
> The reason I asked for your HZ value was to make sure that the stall
> detection was 3 seconds (750 jiffies).  If you had been running a
> 75HZ system (admittedly unlikely) you would have seen a 10-second stall,
> and the patch would not help.  In that case, the right thing to do would
> have been to work out why the system was spinning for 10 seconds during
> boot -- tough to get a 5-second boot when the system spins for 10
> seconds coming up, right?  ;-)

That patch fixes the rcu error.

odr:/# grep -i rcu t
[    0.000000] RCU-based detection of stalled CPUs is enabled.



Folkert van Heusden

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