linux-kernel - Re: [Patch V1 1/3] x86, mce: MCE log size not enough for high core parts

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Date:	Thu, 24 Sep 2015 17:47:22 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Ashok Raj <ashok.raj@...el.com>
Cc:	linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [Patch V1 1/3] x86, mce: MCE log size not enough for high core
 parts

On Thu, Sep 24, 2015 at 01:48:38AM -0400, Ashok Raj wrote:
> MCE_LOG_LEN appears to be short for high core count parts. Especially when
> handling fatal errors, we don't clear MCE banks. Socket level MC banks
> are visible to all CPUs that share banks.
> 
> Assuming 18 core part, 2 threads per core 2 banks per thread and couple uncore
> MSRs. Rounding to 128 with some fudge to grow in future.
> 
> Signed-off-by: Ashok Raj <ashok.raj@...el.com>
> Suggested-by: Tony Luck <tony.luck@...el.com>
> ---
>  arch/x86/include/asm/mce.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/mce.h b/arch/x86/include/asm/mce.h
> index 2dbc0bf..4293ae7 100644
> --- a/arch/x86/include/asm/mce.h
> +++ b/arch/x86/include/asm/mce.h
> @@ -88,7 +88,7 @@
>  #define MCE_EXTENDED_BANK	128
>  #define MCE_THERMAL_BANK	(MCE_EXTENDED_BANK + 0)
>  
> -#define MCE_LOG_LEN 32
> +#define MCE_LOG_LEN 		128
>  #define MCE_LOG_SIGNATURE	"MACHINECHECK"

Hmm, I don't think this is what I meant when we talked about it
previously. So let me try again:

Now that we have this shiny 2-pages sized lockless gen_pool, why are we
still dealing with struct mce_log mcelog? Why can't we rip it out and
kill it finally? And switch to the gen_pool?

All code that reads from mcelog - /dev/mcelog chrdev - should switch to
the lockless buffer and will iterate through the logged MCEs there.

I think this way we're much better prepared for future machine sizes.
We can even use memblock to allocate appropriate memory at boot for the
gen_pool if the 2 pages are not enough.

Hmmm?

-- 
Regards/Gruss,
    Boris.

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