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Old 2013-08-03, 15:23   #1
Jud McCranie
 
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Default Iteration times in i5 and i7

I'm using Prome95 for the Seventeen or Bust project. I've been running four exponents on a quad-core i7 for quite a while, I am now testing exponents in the 24.7 million range. A test on the i7 takes a little less than 7 days and iteration times are around 21-22 ms.

A few days ago I added a quad-core i5, also running four exponents. At first it was also showing iteration times of 22ms. The status shows that the tests will take about 6 days (none finished yet). (They have been running for about 2.5 days and are 30% done, so it may take 8 days.) Then yesterday the iteration times went from 22 to 41. I checked the power settings and made changes to set it for high performance, and the iteration times went back to 22. Then this morning they were back to 40-41. I checked the power settings, and they are OK. I rebooted and they are still at about 41. At 41 the tests are going to take about 11.4 days.

Is there a way to get it back to 22ms iteration times?

Last fiddled with by Jud McCranie on 2013-08-03 at 15:23
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Old 2013-08-03, 19:09   #2
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I have an inkling that you may be feeling the effects of thermal throttling. I assume that these are desktop computers - if so, try and get some better airflow in to the case using a fan. If a laptop, try the Throttle=xx setting in the config file to reduce the amount of CPU time Prime95 runs. If that doesn't work, then just get a cooling stand, like this Zalman cooler from Amazon.
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Old 2013-08-03, 19:42   #3
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Quote:
Originally Posted by f1pokerspeed View Post
I have an inkling that you may be feeling the effects of thermal throttling. I assume that these are desktop computers - if so, try and get some better airflow in to the case using a fan.
They are both desktops. The fan on the new i5 is not making much sound, but I can feel air going in where it should and warmer air going out the back. It has plenty of ventalation. Speccy says that the CPU is running at 55C (in the green) and the motherboard at 28C (also in the green).

So it doesn't seem to be hot. The task manager says that Prime95 is running at 98-99% of the CPU.

I just shut off three of the workers to see if that makes a difference.
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Old 2013-08-03, 20:17   #4
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On the i5:

running only 1 test, the time drops to 17ms per iteration and the CPU cools off to about 43C.

Two tests: 19ms (both) and CPU 49C
Three tests, 25-27ms, CPU 53C
Four tests, 35-38ms, 55C

So I can get more throughput running two tests instead of four! Is there a way to fix this?

----------------
The i7 behaves a little like that, but not as much. Going from 4 to 1 drops the time from 21-22ms to 14-15, and I can hear the fan run slower.
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Old 2013-08-03, 22:27   #5
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The LL test is not easily multi-threaded (or something like that) and therefore does not benefit (greatly) from using more than one core per exponent.

Your problems are arising because you are memory bottlenecked (ie: bandwidth not good enough to handle the amount of data being pushed around). Perform one or two LL tests and then do ECM or P-1 on the other cores to your preference.

Regarding CPU temperatures, do you know the exact i5/i7 model? If so, go to the Intel website and check for their Tcase temps - if the CPU runs within about 5-10 degrees of that (I think) it then implements the thermal throttling. This is just a check process - in case your CPU is running a little off.
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Old 2013-08-03, 22:48   #6
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Not necessarily in this case, I think.

Running all 4 threads(cores) with P95, check Task manager and see how much P95 is using. Also, you might want to see what CPU-Z says...
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Old 2013-08-03, 23:05   #7
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Quote:
Originally Posted by f1pokerspeed View Post
The LL test is not easily multi-threaded (or something like that) and therefore does not benefit (greatly) from using more than one core per exponent. ...

Regarding CPU temperatures, do you know the exact i5/i7 model? If so, go to the Intel website and check for their Tcase temps -
I'm running four tests - each on a different core, not multithreading the test of one exponent.

I do know the exact models of i5 and i7 - I will look up that data.

Since my last message I did some tests on both computers.
On the i7, running 2 gives about 1.9x throughput, running 3 gives 2.3x throughput, and running 4 gives 2.5x throughput.

On the i5, running 2 gives about 1.8x throughput, running 3 gives 2.0x throughput, and running 4 gives 1.7x throughput.

So on the i7 there are diminishing returns, and 4 is only about 9% better than running 3. On the i5, running 4 gives lower performance than running 2 or 3!
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Old 2013-08-03, 23:44   #8
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The task manager says that on the i5, Prime95 is getting almost 100% of the CPU. On the i7 it is getting 50%, because of the hyperthreading.

I can't get CPU-Z to run. The places I found to download it install things I don't want. And after it said that it did install, it took me to a folder where it said the installation would be finished, but the folder was blank.

These are links to both CPU data sheets, and the temperature seems to be OK

http://ark.intel.com/products/65509

http://ark.intel.com/products/52213
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Old 2013-08-03, 23:46   #9
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Quote:
Originally Posted by f1pokerspeed View Post
If so, go to the Intel website and check for their Tcase temps - if the CPU runs within about 5-10 degrees of that (I think) it then implements the thermal throttling.
Do you mean 5-10 degrees below TCase or 5-10 degrees above?
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Old 2013-08-04, 10:25   #10
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Sorry for the late reply, but:

1) below Tcase, anything above for any amount of time would (probably) kill the CPU
2) You probably downloaded the ZIP version of CPU-Z. Here's the installer (with no adware/spyware/etc: http://www.cpuid.com/medias/files/so...5-setup-en.exe
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Old 2013-08-04, 14:24   #11
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Quote:
I can't get CPU-Z to run. The places I found to download it install things I don't want.
He probably tried the exe installer.... try the zip. EDIT: here


Quote:
Originally Posted by Jud McCranie View Post
They are both desktops. The fan on the new i5 is not making much sound, but I can feel air going in where it should and warmer air going out the back. It has plenty of ventalation. Speccy says that the CPU is running at 55C (in the green) and the motherboard at 28C (also in the green).

So it doesn't seem to be hot. The task manager says that Prime95 is running at 98-99% of the CPU.

I just shut off three of the workers to see if that makes a difference.
As again, 55C is perfectly fine for temperatures. I would be worried if it went over 75-80C imo.

Last fiddled with by kracker on 2013-08-04 at 14:26
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