linux-kernel - Re: [PATCH 8/8] ACPI / trace: Add trace interface for eMCA driver

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Date:	Thu, 17 Oct 2013 07:34:43 -0300
From:	Mauro Carvalho Chehab <m.chehab@...sung.com>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
	"Chen, Gong" <gong.chen@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Aristeu Rozanski Filho <arozansk@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 8/8] ACPI / trace: Add trace interface for eMCA driver

Em Wed, 16 Oct 2013 20:47:05 +0000
"Luck, Tony" <tony.luck@...el.com> escreveu:

> > Also, I suspect that, if an error happens to affect more than one DIMM
> > (e. g. part of the location is not available for a given error),
> > that the DIMM label will also not be properly shown.
> 
> There are a couple of cases here:
> 
> 1) There are a number of DIMMs behind some flaky h/w that introduces errors
> that are apparently blamed onto each of those DIMMs.
> 
>   All we can do here is statistical correlations ... each error is reported independently,
>   it is up to some entity to notice the higher level topology connection. There is enough
>   information in the UEFI error record to do that (assuming that BIOS filled out the
>   necessary fields).
> 
> 2) There is a single reported error that spans more than one DIMM.
> 
>   This can happen with a UC error in a pair of lock-step DIMMs.  Since the error is UC
>   we know that two (or more) bits are bad.  But we have no way to tell whether the
>   bad bits came from the same DIMM, or one bit from each (because we don't know
>   which bits are bad - if we knew that, we could fix them :-)   The eMCA case should
>   log two subsections in this case - one for each of the lockstep DIMMs involved. A user
>   seeing this will should probably just replace both DIMMs to be safe.  If they wanted to
>   diagnose further they should swap DIMMs around so this pair are no longer lockstepped
>   and see if they start seeing correctable errors from each of the split pair - or if the UC
>   errors move with one or the other of the DIMMs

There's also a third case: mirrored memories.

As a matter of coherency with hw-based reports, for cases (2) and (3),
the error tracing should be displaying both memories that are affected
by a UC error (or a CE error on a mirrored address space).

Regards,
Mauro
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