linux-kernel - Re: Threaded irqs + 100% CPU RT task = RCU stall

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Date:	Wed, 6 Mar 2013 09:16:48 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Paul Gortmaker <paul.gortmaker@...driver.com>,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Threaded irqs + 100% CPU RT task = RCU stall

On Wed, Mar 06, 2013 at 04:58:54PM +0100, Thomas Gleixner wrote:
> On Wed, 6 Mar 2013, Paul Gortmaker wrote:
> > So, I guess the question is, whether we want to try and make the system
> > fail in a more meaningful way -- kind of like the rt throttling message
> > does - as it lets users know they've hit the wall?  Something watching
> 
> That Joe Doe should have noticed the throttler message, which came
> before the stall, shouldn't he?
> 
> > for kstat_incr_softirqs traffic perhaps?  Or other options?
> 
> The rcu stall detector could use the softirq counter and if it did not
> change in the stall period print: "Caused by softirq starvation" or
> something like that.

The idea is to (at grace-period start) take a snapshot of the CPU's
value of kstat.softirqs[RCU_SOFTIRQ], then check it at stall time, right?

Or do I have the wrong softirq counter?

							Thanx, Paul

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