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mdettweiler 2008-10-17 03:28

[quote=mdettweiler;145628]Yep, 160K. That rules out the possibility of an FFT jump--any other ideas as to what could be causing this?

Maybe my CPU's just getting clogged with dust and it's running slowly because of that? (Then again, I have a little gadget on my taskbar that reads out the current CPU frequency for each core, and they're both already manually set to 2.20Ghz, which is confirmed by the gadget's readout.)[/quote]
Update: I just looked at my iteration times with mprime v25.6 on a 17M (the 896K part of it) Mersenne number that I'm currently doing a doublecheck test on for GIMPS, and compared them with the ratings for similar CPU's on the GIMPS Benchmarks reference page. I was getting very close to 0.030 seconds per iteration, whereas the best times listed for various CPU's similar to mine (they didn't have my model, an Intel E4500, listed) ranged from 0.0214-0.0253 seconds per iteration for the same FFT level.

Long story short: it seems to be quite a sure thing now that my CPU isn't running quite as fast as it should be, which would (at least partially) explain its odd slowness on my Five or Bust range. I'll look into the problem more within the next day or so; the only thing I can think of is dust contamination, since I've seen that slow down my previous CPU (a P4 Prescott 3.2GHz) a lot (though admittedly I wasn't watching the frequency scaling on that one).

Maybe the Ubuntu CPU Frequency Scaling Monitor doesn't detect heat-related scaling, only idle-related scaling? (I always leave the CPU manually set to "Performance" mode to correct for a "feature" in some versions of Ubuntu that causes it to still consider the CPU as idle when lowest-priority apps like prime search apps are running.)

paleseptember 2008-10-24 08:09

For comparison (if this helps), 1420007 is taking 0.005s/iteration on a P4 3.0GHz 32-bit windows xp. Works out at 1.9 hours per test.

jrk 2008-11-12 21:24

Would it be worthwhile to do P-1 on these candidates before doing PRP?

philmoore 2008-11-12 21:52

I did a P-1 run on several hundred candidates and found far too few factors to be worth the cost. On the other hand, as candidates grow in size, I expect that a point will come where P-1 factoring will pay off. Much also depends upon the sieving depth, as well.

paleseptember 2008-12-22 05:00

I've hit the change from 192K FFT length to 224K somewhere in the 1.97M file. Have slowed from 0.004s to 0.005s per iteration (Q6700, windoze xp 32-bit, 3.5GB RAM (apparently)). Of course, we're at 1 significant figure, so those numbers are pretty arbitrary :)

It would be nice if we could find a probable prime this year! *lets the machines keep crunching away*

paleseptember 2009-02-09 05:52

Taking 2.70-2.74M (four files, work computer)

Ladida (Up to the 320K FFT length. The slowest from 224K (seem to have missed 256K altogether) on my Q6700 is from 0.005 to 0.007s/iteration. Still better than my Q6600 at home which is clocking 0.010s/iteration at 256K FFT. There's something wrong with it, and I can't work out what!)

mdettweiler 2009-02-09 16:57

[quote=paleseptember;162162]Still better than my Q6600 at home which is clocking 0.010s/iteration at 256K FFT. There's something wrong with it, and I can't work out what!)[/quote]
Have you tried cleaning out the CPU fan and heatsink? If dust accumulates there it can slow a computer down a *lot*. I used a typical household canister vacuum to clean mine on a number of occasions and each time it's gotten its second wind back. :smile:

Batalov 2009-02-09 18:54

Are you using [URL=""]Core Temp[/URL]? It's a good indicator when the cleaning is needed.
My home Q6600 runs at 0.004 sec/iter @ 256K.

I've found that at least twice a year you may even want to take apart the tower (or a similar device) because invisible from the outside it gets full with dust and you may even lose the fan motor and then all the hell will break loose.

External dusting for the sink is good at least every month, surely.

[SIZE=1]When a runner find his second breath, he emits his [/SIZE][URL=""][SIZE=1]second wind[/SIZE][/URL][SIZE=1]?[/SIZE]

paleseptember 2009-02-09 21:53

Ta Batalov, mdettweiler, for the advice. I'll pull my box apart this weekend and delicately attempt some cleaning. I'll also try that program you recommended Batalov, it looks helpful.

What OS are you using for PRP? I'm on WinXPPro 32-bit with 2GB of RAM. I've left all the options for prime95 as standard. Should I be bumping the memory allocation?

My computer knowledge is pretty woeful I'm afraid. (As is my number theory knowledge if previous conversations with Phil are to go on :smile:)

engracio 2009-02-09 22:26


Definitely download the core temp proggieand have it monitor the cpu temp. Most dc'er are also overclockers. All of them know that the number one enemy of the cpu is overheating. Cleaning out the inside of the box is a big step in lowering the cpu temp. Knowing the temp is a must. Try to run the core temp as soon as you can download it so that you know what is your baseline.

On this box I have a q6600 running all 4 cores 100% plus two gpu2 video cards folding. Those 2 video cards produces lots of heat. The highest cpu temp I feel comfortable with is 70c which is where it is at this time. To some it is too high, to others its acceptable.

A possibility of why your prp time is .0010 instead of .007 or 6 is because the mobo thinks it is overhaeting and stepping down the cpu. Let us know your cpu temp.

Batalov 2009-02-10 07:09

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[quote=paleseptember;162162] Q6600 at home which is clocking 0.010s/iteration at 256K FFT. There's something wrong with it, and I can't work out what!)[/quote]

Aaah. I get now what is most wrong. It's the top of the summer down there! It is hot [sarcasm] ...even in our coastal little town in August. [/sarcasm] (In truth, not really. There's probably only Hawaii that is milder than here. But still a systematic 10"C higher summer temp brings the hardworking comp to a point of confusion.)

Same (more, really) for you in February. You do have to be gentle to the comp in summer. Maybe lower the FSB by 5%, let it live a little. Better than throttling! Or get a Tuniq Tower (or something like it), and you will shave 10-15"C off that core temperature.

P.S. Ah yes, btw, to your question: My home system is a WinXP Pro, too. The CoreTemp is very nicely designed and doesn't take space (sits in the corner), and it logs, too. (E.g. you can set it to log once a minute... Later, you may plot the temps with something like Excel and see the trend). (below)

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