Most new 10^20 tasks on my 32 core Xeon machine completes in about 0.5 hour, but there are sone significantly longer, for example this one (link below) took almost 7 hours! Recently I also aborted one which after 7.5h was at 75%, assuming that it hung and won't complete. However when I looked on completed task list, I found that it might complete successfully. Why some tasks are significantly longer that others?

Completed task: https://sech.me/boinc/Amicable/result.php?resultid=4799087
Aborted task: https://sech.me/boinc/Amicable/result.php?resultid=4799109

Edit: CPU time for this task is about 7 hours, so average CPU usage calculated as run time divided by CPU time is 26%. This is very low. I checked some other task which competed in about 0.5h (4798397) and got 63%. Does it mean that thread synchronization was so bad? Should I lower number of CPUs for WUs and run few in parallel?

Edit2: I have one more tasks in progress, now for almost 5h. "top" command now shows 100%, about minute ago it was 200%. 1 to 2 out of 32 CPUs used is very bad result.

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A small portion of WUs can't be parallelized to many threads. The one that you aborted had command line /from 2*5*7*11*389*31249 /to 2*5*7*11*389*31271 /task_size 1938395193 which means it could run only 4 threads in parallel (31249, 31253, 31259, 31267 as the last prime number in factorization). But such WUs are rare.

You can change preferences to use max. 4 threads per WU. They'll take more time to complete, but the total CPU load will always be good.

You can change preferences to use max. 4 threads per WU. They'll take more time to complete, but the total CPU load will always be good.

Thanks, looks that I will have to do this. Although it would be a better idea if server could send tasks in more smart way and try to sent such tasks to hosts which have smaller number of CPUs, which matches actual WU limit.

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more than 1 hr to finish a single wu ? with 100% cpu and gpu usage ?
used to be only 15 mins, all of my cards are showing this.
something wrong ???????

Are you talking about GPU version? It varies depending on WU - some ranges get processed fast (compared to CPU), some don't.

P.S. The project started the new subrange "2^2*11*..." a few days ago, so it's normal that WU run times changed.

more than 1 hr to finish a single wu ? with 100% cpu and gpu usage ?
used to be only 15 mins, all of my cards are showing this.
something wrong ???????

Actually, there is something wrong with your settings. You've set kernel size for NVIDIA GPUs to 18 which is too small for GTX 1070/1080. Set it to at least 21 here: https://sech.me/boinc/Amicable/prefs.php?subset=project

P.S. I've set it to 21 for you, but you can always change it to whatever value you want. Let's hope it improves WU run times.

thanks, cheers. :)

thanks, cheers. :)