linux-kernel - Re: AMD Athlon bogus performance value causing RCU stalls?

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Date:   Sun, 23 Sep 2018 17:54:22 -0400
From:   Rob Prowel <rprowel@...cast.net>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: AMD Athlon bogus performance value causing RCU stalls?

On 09/23/18 17:19, Thomas Gleixner wrote:

>>
>> What is that value for the second Athlon core (seems extremely bogus), and
>> would/could that be the reason for the schedule_timeouts?  This bogus value
>> also shows up in the bootup log when the second core is activated.  Seems to
>> be AMD specific, as the values are correct on my Xeon machines.
> 
> That's a 32bit machine I assume.

No.  Actually it is a 64 bit AMD Athlon.  Might need to check the math being a
problem in the 64 bit domain as well.

> 
> Yes. This was decoded recently as an issue on 32bit due to a calculation
> which is based on 'unsigned long' but requires to be 64bit wide.
> 
> It's in the 4.18.8 stable kernel, which should be available from your
> fedora repo anytime soon.
> 

Will check with the newer kernel when it's available but please do double check if this
problem might exist on 64 bit architectures as well...and of course I'm interested to
know whether it is the likely cuprit of my RCU problem.