linux-kernel - Re: [PATCH] RAS: Add a tracepoint for reporting memory controller events

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Message-ID: <20120531172018.GO14515@aftab.osrc.amd.com>
Date:	Thu, 31 May 2012 19:20:18 +0200
From:	Borislav Petkov <bp@...64.org>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Linux Edac Mailing List <linux-edac@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Aristeu Rozanski <arozansk@...hat.com>,
	Doug Thompson <norsk5@...oo.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] RAS: Add a tracepoint for reporting memory controller
 events

On Thu, May 31, 2012 at 04:51:27PM +0000, Luck, Tony wrote:
> No, it's a 6-bit field used as a shift ... so if it has value "6", it
> means cache line granularity. Value "12" would mean 4K granularity.
> Architecturally it could say "30" to mean gigabyte, or even "63" to
> mean "everything is gone".

Right, 0x3f are 6 bits, correct, doh!

> >> while a few (IIRC patrol scrub) will report with page (4K)
> >> granularity. Linux doesn't really care - they all have to get rounded
> >> up to page size because we can't take away just one cache line from a
> >> process.
> >
> > I'd like to see that :-)
> 
> Patrol scrub works inside the depths of the memory controller on rank/row
> addresses, not on system physical addresses. When it finds a problem, a
> reverse translation is needed to be able to report a system physical
> address in MCi_ADDR. Getting all the bits right is apparently a hard thing
> to do, so the MCI_MISC_ADDR_LSB bits are used to indicate that some low
> order bits are not valid.

Ok, thus the dynamic granularity. But we're going to end up reporting
rank and row too so that it can be matched to the DIMM. I consider
physical address a bonus in such cases and it is only of importance to
those who like to replace single DRAM chips or single MOSFET transistors
:-) :-) :-).

-- 
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Boris.

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