Definitely a thermal problem.

As root,

[code]
dd if=/sys/devices/pci0000:00/0000:00:18.3/config bs=1 count=256 | od -Ax -tx1
[/code]
and the byte at offset 0x64, which is normally 0x25, goes to 0x35 when the processor overheats; similarly, model-specific register C0010071 (which can be read with rdmsr utility downloaded from [url]http://www.kernel.org/pub/linux/utils/cpu/msr-tools/msr-tools-1.1.2.tar.bz2[/url]) has bit 16 change from 0 to 1, indicating overheating, seventeen seconds after I start the job and changes from 1 to 0 six seconds after the job finishes.

A piece of cake. Would it really have been too much effort to have a little light on the case light up when it overheats, or maybe a quiet beeping noise? At least the kernel exposes the MSRs and PCI config space nicely, I was afraid I'd have to write a module!

What I don't know is whether this is a thermal problem to be solved with an enormous heat-sink, or a thermal problem to be solved by telling the BIOS to use different thresholds for processor overheating. I imagine a script that stops the sievers and waits three seconds when the overheating bit gets set, and turns them back on once it's cleared, would not be a way to ensure optimal processor lifetime.

With two sieving processes it overheats after 23 seconds, with one it takes nearly a minute, so given that it'll overheat anyway I might as well run four sievers. If I parse model-specific register C0010065 correctly, it's running at 1250MHz when overheated.

Have you tried to use a 3rd party, non-factory heatsink and some quality thermal paste?

Tom, Try Tuniq Tower, if it is compatible? (goddarn, I couldn't keep up writing with all T's)
I chose it after a few days of reading forums and never got disappointed.
Not terribly expensive.
--Serge

P.S. this is the system for the 5,421- matrix stage, isn't it? you move very fast.

The Barcelonas have treated me well
 

Sorry to hear that the Phenom is not whirring along as it should.

As a benchmark, I'm running a motherboard with two quad-core 2.0 GHz 2350 Barcelonas, and I tend to hit just over 0.7 seconds per relation per core on that same job (gnfs-lasieve4I15e on it, sieving 5^421-1). Per-core performance is about 15% slower than my dual-core 2218 Opterons (2.66 GHz).

So you should expect around 0.57 seconds per core with the Phenom.

Whatever else you can say about AMD, the quad-core processors run nearly independently of one another on these giant sieving jobs.

[QUOTE]Have you tried to use a 3rd party, non-factory heatsink and some quality thermal paste?[/QUOTE]

This could be critical. I put some monster sinks on the Barcelonas, and the fans blow even when it's cold in the room. For 75W processors, the Barcelonas really put out plenty of heat. Something about being run flat out will do that.

I replaced the motherboard with a Gigabyte MA78GPM-DS2H, which took about half an hour and left my fingers covered in AMD's finest grey thermal goop. Still using the AMD standard heatsink.

This resolved the problem:

[code]
total yield: 234496, q=79248229 (0.90472 sec/rel)
total yield: 234525, q=79248233 (0.90471 sec/rel)
total yield: 234562, q=79248241 (0.90467 sec/rel)

total yield: 46, q=79248277 (0.52630 sec/rel)
total yield: 65, q=79248311 (0.56108 sec/rel)
total yield: 105, q=79248331 (0.46371 sec/rel)
[/code]

and on a different number
[code]
total yield: 1092888, q=53223553 (0.18429 sec/rel)
total yield: 1092930, q=53223557 (0.18429 sec/rel)
total yield: 1092969, q=53223563 (0.18429 sec/rel)
total yield: 86, q=53223589 (0.09477 sec/rel)
total yield: 178, q=53223629 (0.09118 sec/rel)
total yield: 256, q=53223689 (0.09496 sec/rel)
total yield: 342, q=53223701 (0.09456 sec/rel)
[/code]

Happy now, if poorer; now begins the cheery fun process of getting a refund on the other motherboard.

[QUOTE=fivemack;143057]I replaced the motherboard with a Gigabyte MA78GPM-DS2H[/QUOTE]

Exactly the one I have (with a Phenom X4 9350e). I'm quite happy with the board, the graphics is surprisingly fast for an on-board GPU. My only grief is that the BIOS won't let you set the RAM voltage any lower than 1.95V, and won't let you use only SidePort RAM for the video either - it always takes at least 128MB of main memory. Maybe these will get fixed with a BIOS update.

Alex