kernel MCA messages

Jeremy Chadwick freebsd at
Tue Aug 24 23:38:53 UTC 2010

On Tue, Aug 24, 2010 at 07:13:23PM -0400, Dan Langille wrote:
> On 8/22/2010 9:18 PM, Dan Langille wrote:
> >What does this mean?
> >
> >kernel: MCA: Bank 4, Status 0x940c4001fe080813
> >kernel: MCA: Global Cap 0x0000000000000105, Status 0x0000000000000000
> >kernel: MCA: Vendor "AuthenticAMD", ID 0xf5a, APIC ID 0
> >kernel: MCA: CPU 0 COR BUSLG Source RD Memory
> >kernel: MCA: Address 0x7ff6b0
> >
> >FreeBSD 7.3-STABLE #1: Sun Aug 22 23:16:43
> FYI, these are occurring every hour, almost to the second. e.g.
> xx:56:yy, where yy is 09, 10, or 11.
> Checking logs, I don't see anything that correlates with this point
> in the hour (i.e 56 minutes past) that doesn't also occur at other
> times.
> It seems very odd to occur so regularly.

1) Why haven't you replaced the DIMM in Bank 4 -- or better yet, all
   the DIMMs just to be sure?  Do this and see if the problem goes
   away.  If not, no harm done, and you've narrowed it down.

2) What exact manufacturer and model of motherboard is this?  If
   you can provide a link to a User Manual that would be great.

3) Please go into your system BIOS and find where "ECC ChipKill"
   options are available (likely under a Memory, Chipset, or
   Northbridge section).  Please write down and provide here all
   of the options and what their currently selected values are.

4) Please make sure you're running the latest system BIOS.  I've seen
   on certain Rackable AMD-based systems where Northbridge-related
   features don't work quite right (at least with Solaris), resulting
   in atrocious memory performance on the system.  A BIOS upgrade
   solved the problem.

There's a ChipKill feature called "ECC BG Scrubbing" that's vague in
definition, given that it's a "background memory scrub" that happens at
intervals which are unknown to me.  Maybe 60 minutes?  I don't know.
This is why I ask question #3.

For John and other devs: I assume the decoded MCA messages indicate with
absolute certainty that the ECC error is coming from external DRAM and
not, say, bad L1 or L2 cache?

| Jeremy Chadwick                                   jdc at |
| Parodius Networking              |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |

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