[feizaghaee]

hi. does anybody know how can i use whole capacity of my core i7 cpu (i mean 8 core of cpu). i can work with 4 core of my cpu but task manager shows 50% cpu usage. i want to know when task manager shows 50% usage how many cores are working and can i run a problem with 100% cpu usage. when i run CFX solver i choose MPICH parallel for windows with 4 partitions. can i choose 8 partitions how? my Ansys CFX's version is 11.

[jbritton]

see link: http://www.cfd-online.com/Forums/cfx/72094-cfx-i7.html

[feizaghaee]

this topic dosen't contain whole of my questions. 50% usage of task manager isn't discussed. i want to know how many cores are working.

[Michiel]

50% of 8 is 4... The numbers 4 and 8 are mentioned in the other topic.

[jbritton]

^^^ lol,

Thank you for saving me the effort.

If memory serves me CFX 11 will only run on 2 cores unless you have additional parallel licenses enabling further processors to run. A core can be called a processor in this case.

So 50% load means you running it on 2 cores(4/100*50=2)or (4/2=2), this may well show up as 4 but this is due to hyperthreading.

With hyperthreading the theoretical number of cores is 8 again (8/100*50=4) so yes 4 is 50% of 8

In the writing of this my IQ feels like it has dropped 50% because all of this was discussed in the other thread!

[feizaghaee]

thanks a lot. i asked this question becuase in that topic, 4 cores was mentioned as whole capacity of core i7 and 8 cores was mentioned as result of hyperthreading technology but CFX dosen't take any advantages from this feature. but you said 4 cores are half of the capacity. using 8 cores was mentioned useless. how can i install parallel license. tanks

[ghorrocks]

Installation of parallel licenses is discussed in the CFX manual. If you currently have 4 parallel licenses but wish to waste money by running 8 processes on a single i7 CPU then talk to your CFX rep to purchase extra licenses.

I think I said that in the other thread didn't I? It's deja vu all over again. (That was meant to be a bad joke by the way)

[feizaghaee]

tanks a lot for your kind attention

[murx]

I want to get back to this topic again.
In my case licenses are not the constraint. I have enough licenses available to run CFX on 8 cores.

Glenn, in the other thread you said

CFX has not been complied to use hyperthreading. Don't use it. Just leave the virtual cores sit idle or even better disable them in the BIOS.

I absolutely understand that using all 8 virtual cores does not give me a huge advantage. But if I let 4 of the virtual cores sit idle, isn't that a huge disadvantage compared to disabled hyperthreading? Because... like soembody said in this thread... Windows taskmanager shows only 50% CPU load.

So if I have enough licenses available, isn't it better to use all 8 cores? And is there rough estimate how much using 8 cores in hyperthreading is inferior to using 4 cores with hyperthreading disabled?

[ghorrocks]

Do the test yourself then! Run a benchmark case with 4 processes and another with 8. I bet the 8 case is either barely faster than the 4, or more likely to be slower.

[murx]

Ok, I did the test. Here's the results, for those who are interested:




What I did was a one-phase simulation on a mesh with approx. 2 Mio. elements. I ran the simulation in HP MPI Local Parallel except for the 1core run - that was run in serial mode. I measured the time for 10 outer loops. The value in the chart is the inverse of this time, normalized with the 1-core value.

[evcelica]

great, thanks for doing this. Do you have results with hyperthreading disabled to see how that affects performance?

[murx]

Unfortunately, I don't think I am authorized to change any BIOS settings. But I will reboot and try to do so as soon as my current simulation is finished.

[ghorrocks]

I assume you have a 4 core CPU - in that case the 4 core result will be close enough to the no-hyperthreading result.

A speedup factor of 2 at 4 cores on a modern CPU is not very good. You should be able to do better than that. What CPU do you have? Are you sure you are not running out of memory?

[evcelica]

Glenn, are you saying having hyper-threading on is better for CFX?
(8 with HT is better than 4 w/o) and (4 with HT is equal to 4 w/o)? roughly of course.


I was somewhat disappointed by this scaling too, what are the specs on your memory?

[ghorrocks]

CFX has not been compiled to make use of hyperthreading. On or off it will not make much difference.

My question about memory is because a possible explanation of the poor performance is you have run out of memory and the machine is paging. You will not get a good parallel speed up if it is paging.

[murx]

The CPU is an i7-2600 and the memory size is 8 GB. I do not remember the exact memory usage during those test runs. But on similar runs, the amount of memory used is about 4.5 GB.

I expected a bigger speedup factor, too.

[ghorrocks]

What time are you reporting? The setup and shut down of a simulation does not scale with multi processors, only the solver time. If you look in the output file the solver time is reported after the last iteration, and the total time is reported at the end.

You should only use solver time to work our speed up factors.

[murx]

I actually measured the time by hand using the windows clock, since I did not care for a very high precision

My start time was the time when the first iteration step started and the stop time was the time when the last residuals of the 10th iteration step were plotted. So i did not count for the time necessary for mesh partitioning and so on...

[ghorrocks]

OK, but it is easier to use the time recorded in the output fine. Then you don't need to watch text files scroll past. More accurate too.