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

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Message-ID: <51376B5D.7040108@windriver.com>
Date:	Wed, 6 Mar 2013 11:14:21 -0500
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	<linux-rt-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: Threaded irqs + 100% CPU RT task = RCU stall

On 13-03-06 10:58 AM, 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?

Actually it isn't showing up at all -- just the RCU stall itself.
Now that you mention it, I do wonder why the throttler message 
isn't tripped though...

Paul.
--

> 
>> 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.
> 
> Thanks,
> 
> 	tglx
> 
> 
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