linux-kernel - Re: [PATCH 3/3] ghes_edac: add platform check to enable ghes

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Message-ID: <20170721172344.GA11316@nazgul.tnic>
Date:   Fri, 21 Jul 2017 19:23:45 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Mauro Carvalho Chehab <mchehab@...pensource.com>
Cc:     "Kani, Toshimitsu" <toshi.kani@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "srinivas.pandruvada@...ux.intel.com" 
        <srinivas.pandruvada@...ux.intel.com>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>
Subject: Re: [PATCH 3/3] ghes_edac: add platform check to enable ghes_edac

On Fri, Jul 21, 2017 at 02:01:31PM -0300, Mauro Carvalho Chehab wrote:
> I see the value of having a threshold in BIOS, provided that it is
> well documented, and whose value can be adjusted, if needed.
> 
> One of the things I wanted to implement in ras-daemon were an
> algorithm that would be doing such threshold in software.

We have that now in the kernel: drivers/ras/cec.c

We did it exactly for that purpose - not upsetting users unnecessarily.

> The thing with a BIOS threshold is that the user has no way to
> audit the algorithm. So, when BIOS start reporting such errors,
> it may be already too late: the systems may be in the verge of 
> losing data (or some data was already lost).

Not only that: thresholds depend on the DIMM types which means, BIOS
must know what DIMM types are in there which I doubt. So exposing that
to configuration instead of "deciding" for people would be better.

> That's critical on cluster systems with thousands of machines:
> while the impact of disabling a cluster node to do some maintainance
> is marginal, the impact of an uncorrected error on a single
> machine may compromise weeks of expensive processing.
> 
> That's why some users prefer to monitor every single corrected
> error, and compare with the probability distribution they
> know that the risk of uncorrected errors is acceptable.

Yap, you need to have stuff like that configurable - BIOS can't predict
all possible use cases.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--