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

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Message-ID: <38932eb1-921f-55f7-10c8-358f9aae32b2@comcast.net>
Date:   Wed, 26 Sep 2018 19:38:09 -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:
>>
>> Other than RTFM, or please build a bunch of kernels from source on your slow
>> machine, using differing config options to help track down the cause of
>> this...any thoughts about a solution?
> 
> 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.

OK.  Followup on AMD performance counter problem in 4.18.7

The Dell machine I was experiencing the problem on had a lot of ACPI
issues.  One of the invalid ACPI entries was for a system timer.
dmesg suggests that the broken timer was used in calculating the
Athlon performance value.  So no, 32/64 bit math was not the issue.

ACPI=off in the kernel boot line fixed the issue completely. Machine
still functions well as a file/web/postgresql dev server so it's all
good.

tanks!