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SubjectRe: [PATCH 8/8] ACPI / trace: Add trace interface for eMCA driver
Em Wed, 16 Oct 2013 20:47:05 +0000
"Luck, Tony" <tony.luck@intel.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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