linux-kernel - Re: [PATCH 3/3] mce: acpi/apei: trace: Enable ghes memory error trace event

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Date:	Thu, 15 Aug 2013 18:11:53 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Mauro Carvalho Chehab <m.chehab@...sung.com>
Cc:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
	tony.luck@...el.com, bhelgaas@...gle.com, rostedt@...dmis.org,
	rjw@...k.pl, lance.ortiz@...com, linux-pci@...r.kernel.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mce: acpi/apei: trace: Enable ghes memory error
 trace event

On Thu, Aug 15, 2013 at 11:14:07AM -0300, Mauro Carvalho Chehab wrote:
> I don't see why should we have those two alternatives, as, at worse
> case (e. g. if ghes_edac can't enrich the APEI data with labels),
> they'll basically provide the very same data to userspace, and the
> EDAC extra overhead is small, on its error report logic.

Well, a couple of reasons.

The first and foremost one is having another layer which needs
registration, etc. because ghes_edac pulls the whole edac core stuff
with it. The thinner we are, the less overhead we cause. And this is
a must for RAS.

Actually, this is a must for all kernel code - the faster we can get
done and the thinner we are, the better. We absolutely definitely don't
want to have a useless layer in the error reporting path just because it
is easier.

This short path will pay out later in error storms and other
resources-constrained situations.

Furthermore, dealing with another edac driver is not trivial for
distros, like going around and telling people that all of a sudden
they need to enable ghes_edac. This is tangential to the issue which
Naveen raised that on some machines, you want not only ghes_edac but the
platform-specific one. Which doesn't work currently and we don't have a
clear solution on how to get it working yet.

Finally, userspace doesn't care where it gets its TP data from as long
as it is there.

> The risk of doing the very same thing on two different places is that
> the logic to encapsulate APEI data into trace_mc_event() would be on
> two separate places. It risks that someone would change one of the
> drivers and forget to apply the very same change on the other, causing
> parse errors on userspace, depending on the source.

We'll make sure that doesn't happen.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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