CPU Power

[LetterC67]

Hello guys! Sorry if my question is stupid
I'm folding with my laptop (i5-4200U) (I don't have good hardware but I still want to help the scientist to find a treatment for Covid-19). It has 4 logical cores. Normally, I set CPU at low (1 core) while I'm working with my laptop. I estimated that it will take about 10s for the CPU to complete 0.01%. Today I changed CPU power to Medium (3 cores), and it takes 7.5s to complete 0.01%. I think that it must be 3x faster. Can anyone explain?

[JimboPalmer]

Welcome to Folding@Home!

I think I can.

When a Work Unit starts, it sees the number of threads allowed (F@H calls them CPUs) and uses that number.

While a WU is running, you can lower that number of threads, but raising it will not change anything until the next WU.

I hope that is clear.

[LetterC67]

Thank you, now I understand! But before starting folding that WU, I set CPU power to Medium so I can lower the CPU usage and compare them. As I have said, my computer takes 10s to complete 0.01% with 1 thread running. I think it must be 3.3s when it uses 3 threads (but 7.5s). I find it confusing Hope you can help me with my problem!

[JimboPalmer]

If you read the log during start up of a WU, you may see -np and -nt then a number, that is the maximum number of CPUs that will be allowed during that WU.

You can lower that.

[_r2w_ben]

Your i5-4200U has 2 cores/4 threads. When scheduling 3 threads, there may be an in balance when 2 threads share a physical core and 1 thread gets an entire core to itself. Work has to wait until all three threads finish on a regular basis to exchange information. The threads that ended up on the same physical core will take longer to reach the exchange point.

I wouldn't expect a 3x speedup. If you go into the more advanced slot settings within configuration, and manually specify 2 CPUs, I think you will see close to 2x improvement. Manually setting to 4 CPUs should give you more than 2x but less than 3x. If you are also folding on the GPU, then you can't go to 4 CPUs because that will slow down the GPU.