Re: THP broken on OCTEON?

[Joshua Kinard <kumba@gentoo.org>]

On 05/23/2016 14:52, Aaro Koskinen wrote:
> On Mon, May 23, 2016 at 09:21:22AM -0700, David Daney wrote:
>> On 05/23/2016 08:20 AM, Ralf Baechle wrote:
>>> On Mon, May 23, 2016 at 06:13:46PM +0300, Aaro Koskinen wrote:
>>>> I'm getting kernel crashes (see below) reliably when building Perl in
>>>> parallel (make -j16) on OCTEON EBH5600 board (8 cores, 4 GB RAM) with
>>>> Linux 4.6.
>>>>
>>>> It seems that CONFIG_TRANSPARENT_HUGEPAGE has something to do with the
>>>> issue - disabling it makes build go through fine.
>>>>
>>>> Any ideas?
>>>
>>> I thought it was working except on SGI Origin 200/2000 aka IP27 where
>>> Joshua Kinard (added to cc) was hitting issues as well.
>>>
>>> Joshua, does that similar to the issues you were hitting?
>>
>> There is nothing OCTEON specific in the THP code, or huge pages in general.
>>
>> That said, we have seen other THP related failures, and have never been able
>> to find the cause.
>>
>> If someone can come up with a reproducible test case that triggers quickly,
>> we can run it in our simulator and easily find the problem.
> 
> Trying to build Perl is a reliable reproducer. Is that too heavyweight
> for your simulator?
> 
> I was able to reproduce this also on EdgeRouter Pro, but there the kernel
> does not fail, only compiler dies with SIGBUS:
> 
> [  315.095264] Data bus error, epc == 0000000000a801c4, ra == 0000000000a80624
> 
> And without THP the build is fine.
> 
> I also tried CN68XX board with 16 GB RAM and also there I get SIGBUS failure
> instead of Machine Check.

SIGBUS is closer to what I was seeing on IP30/IP27, but there's two different
SIGBUS errors in MIPS, a Data Bus Error (DBE) and Instruction Bus Error (IBE).
 I've only seen IBEs result from using THP on Octane/IP30 and Origin/Onyx2/IP27.

Also CC'ing Alastair Bridgewater (nyef), who was working on bringing up the
IP35 hardware (Origin 300/350), as he had been working on tracing down some
possible issues in the TLB code.  He had a small test case at the below address
(use annotation #2), but I don't know if he got any further on debugging it.

http://paste.lisp.org/display/305809#2

-- 
Joshua Kinard
Gentoo/MIPS
kumba@gentoo.org
6144R/F5C6C943 2015-04-27
177C 1972 1FB8 F254 BAD0 3E72 5C63 F4E3 F5C6 C943

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