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

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Date: Tue, 18 Jun 2024 17:35:33 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "$(name)" <qirui.001@...edance.com>, "bp@...en8.de" <bp@...en8.de>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com"
	<mingo@...hat.com>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "hpa@...or.com" <hpa@...or.com>
CC: "x86@...nel.org" <x86@...nel.org>, "linux-edac@...r.kernel.org"
	<linux-edac@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] x86/mce: count the number of occurrences of each MCE
 severity


> In the current implementation, we can only know whether each MCE
> severity has occurred, and cannot know how many times it has occurred
> accurately. This submission supports viewing how many times each MCE
> severity has occurred.

Is know how many times each case was hit useful? The original commit
for this code said it was just to check coverage for the mce-test suite.

4611a6fa4b37 ("x86, mce: export MCE severities coverage via debugfs")

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?

> Due to the limitation of char type, the maximum supported statistics are
> currently 255 times
>
> Signed-off-by: Rui Qi<qirui.001@...edance.com>
> ---
>  arch/x86/kernel/cpu/mce/severity.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
> index dac4d64dfb2a..a81e34c6e3ee 100644
> --- a/arch/x86/kernel/cpu/mce/severity.c
> +++ b/arch/x86/kernel/cpu/mce/severity.c
> @@ -405,7 +405,7 @@ static noinstr int mce_severity_intel(struct mce *m, struct pt_regs *regs, char
>                       continue;
>               if (msg)
>                       *msg = s->msg;
> -             s->covered = 1;
> +             s->covered++;

Wraparound sets this back to zero. Should this be:

	if (s->covered < 255)
		s->covered++;

[Is there a #define for max value in an unsigned char? I could find one. If there is,
then use that instead of hard coded 255]

>
>               return s->sev;
>       }-- 

-Tony