linux-kernel - RE: [PATCH] x86/mce: count the number of occurrences of each MCE severity

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Message-ID: <SJ1PR11MB6083E1173846A5C8B4529D25FCC82@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Thu, 20 Jun 2024 16:20:20 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "$(name)" <qirui.001@...edance.com>
CC: "bp@...en8.de" <bp@...en8.de>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "hpa@...or.com" <hpa@...or.com>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "x86@...nel.org" <x86@...nel.org>
Subject: RE: [PATCH] x86/mce: count the number of occurrences of each MCE
 severity

You seem to have problems with the e-mail infrastructure. I got a few extra copies
of this in HTML format. This one is in plain text, but the From: header says "$(name)"

> > So you either covered a case in the severities table, or you didn't. Does it
> > help to know that you covered a case multiple times?
> >
>
> In the fault injection test in the laboratory, we inject errors multiple
> times and need a counter to tell us how many times each case has
> occurred and compare it with the expected number to determine the test
> results

In my testing on Intel/x86 I don't always see a 1:1 mapping between my
test, and the severities rule. This is because of a h/w race between the
memory controller reporting the error when it sees an uncorrectable ECC
issue, and the core trying to consume the poisoned data. If the memory
controller signal wins the race, Linux takes the page offline and there isn't
a poison consumption error, just a page fault.

> In the production environment, the counter can reflect the actual number
> of times each MCE error type occurs, which can help us detect the MCE
> error distribution of large-scale Data center infrastructure

That could be useful.

> >> Due to the limitation of char type, the maximum supported statistics are
> >> currently 255 times
> >>
>
> How about changing char to u64, which is enough for real-world
> situations and won't waste a lot of memory?

u64 seems like serious overkill. A change from "unsigned char" to "unsigned int"
would keep track of 4 billion errors. That seems like plenty :-)

-Tony