linux-kernel - RE: [PATCH v2 0/2] Update mce

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Date: Thu, 25 Jan 2024 19:19:22 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: Borislav Petkov <bp@...en8.de>, Avadhut Naik <avadhut.naik@....com>
CC: "linux-trace-kernel@...r.kernel.org" <linux-trace-kernel@...r.kernel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>, "x86@...nel.org"
	<x86@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "yazen.ghannam@....com"
	<yazen.ghannam@....com>, "avadnaik@....com" <avadnaik@....com>
Subject: RE: [PATCH v2 0/2] Update mce_record tracepoint

> > The first patch adds PPIN (Protected Processor Inventory Number) field to
> > the tracepoint.
> >
> > The second patch adds the microcode field (Microcode Revision) to the
> > tracepoint.
>
> This is a lot of static information to add to *every* MCE.

8 bytes for PPIN, 4 more for microcode.

Number of recoverable machine checks per system .... I hope the monthly rate should
be countable on my fingers. If a system is getting more than that, then people should
be looking at fixing the underlying problem.

Corrected errors are much more common. Though Linux takes action to limit the
rate when storms occur. So maybe hundreds or small numbers of thousands of
error trace records? Increase in trace buffer consumption still measured in Kbytes
not Mbytes. Server systems that do machine check reporting now start at tens of
GBytes memory.

> And where does it end? Stick full dmesg in the tracepoint too?

Seems like overkill.

> What is the real-life use case here?

Systems using rasdaemon to track errors will be able to track both of these
(I assume that Naik has plans to update rasdaemon to capture and save these
new fields).

PPIN is useful when talking to the CPU vendor about patterns of similar errors
seen across a cluster.

MICROCODE - gives a fast path to root cause problems that have already
been fixed in a microcode update.

-Tony