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Message boards : Problems and Help : PPSE tasks taking much longer than expected

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Joby Kechinsky
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Message 143063 - Posted: 5 Sep 2020 | 14:42:08 UTC

I have recently joined PrimeGrid a few days ago using my computer (processor i5-3337U CPU @ 1.80GHz) running Windows 10. According to the PPSE event, a computer should be able to complete 300 tasks per day. Running four tasks simultaneously, I would expect one batch of four tasks to be completed every 20 minutes by the computer. However, in reality my computer can only complete one batch of four tasks every 3.5 hours, which is 10 times longer than it should be... is there any way that I can increase the speed of task completion?

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Message 143064 - Posted: 5 Sep 2020 | 14:54:08 UTC - in response to Message 143063.
Last modified: 5 Sep 2020 | 14:54:43 UTC

I have recently joined PrimeGrid a few days ago using my computer (processor i5-3337U CPU @ 1.80GHz) running Windows 10. According to the PPSE event, a computer should be able to complete 300 tasks per day. Running four tasks simultaneously, I would expect one batch of four tasks to be completed every 20 minutes by the computer. However, in reality my computer can only complete one batch of four tasks every 3.5 hours, which is 10 times longer than it should be... is there any way that I can increase the speed of task completion?


Hello, and welcome!

Your CPU is a mobile CPU with a low frequency, both of which hamper cumulative performance. Laptops usually have horrible cooling (that's my case at least), and the CPUs cannot keep at its frequency while running max, lowering its already very low freuency. This hampers performance about 30%.
Second, your CPU has 2 cores and 4 hyperthreads. As you will know later, hyperthreading isn't beneficial to running the prime-searching program used at Primegrid, LLR. A solution will be to set "% of CPUs to use" to 50%. This hampers performance by half.
Third, your CPU is an Intel Ivy Bridge CPU which doesn't have a very good AVX implementation, which is used in LLR. You can't change this much. This hampers perf about half.
Lastly, your CPU has 2 cores, which is not the four cores said in the thread. This very logically reduces perf by half.

So 3.5 hrs divided by two (last step), and then divided by two twice (second and third step), then divided by 130% (first step), we get around 20.19 minutes, which is what the post says.
____________
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Joby Kechinsky
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Message 143067 - Posted: 5 Sep 2020 | 16:10:53 UTC - in response to Message 143064.

So, once I set my "% of CPU to use" to 50%, I will effectively double the speed of my computer? And that will be the highest speed that my computer will ever be able to achieve?
It seems quite counterintuitive to me that reducing the CPU usage will increase the speed... but then again, I know nothing about computing and very little about maths because I am only a medical student

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Message 143068 - Posted: 5 Sep 2020 | 16:34:43 UTC - in response to Message 143067.
Last modified: 5 Sep 2020 | 16:37:14 UTC

It is counterintuitive, but it's true. How it was explained to me: your computer has two physical cores, but hyperthreading allows it to pretend it has two more. The two "hyperthreads" work by taking advantage of unused CPU resources. But the LLR app is very good at using up all available CPU resources. Since there are no unused resources for the hyperthreads to use, they don't help.

PS. Since it's easy to get confused: this is "On multiprocessors, use at most []% of the processors" in computing preferences--not the CPU time one. And I believe this advice only applies to LLR, not (e.g.) sieving.

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Message 143070 - Posted: 5 Sep 2020 | 16:58:27 UTC - in response to Message 143067.

So, once I set my "% of CPU to use" to 50%, I will effectively double the speed of my computer? And that will be the highest speed that my computer will ever be able to achieve?
It seems quite counterintuitive to me that reducing the CPU usage will increase the speed... but then again, I know nothing about computing and very little about maths because I am only a medical student


More than double, actually. The decreased power usage should allow for higher sustained CPU frequency. Since you are a medical student, I will make a poor attempt at an analogy (I'm a math guy, but grew up in a medical household):

Think of a core of your CPU as your brain. You are scheduled to perform surgery on two patients. 100% CPU (using hyperthreads) would be doing a little operating on one patient while keeping your eye on the other, then stopping to wash and change to spend a little time operating on the other patient with your eyes on the first, and back and forth until they're done. Lots of time/resources wasted on the washing and changing in between, efficiency lost to looking at the wrong body, plus reorienting yourself to where you were when you stopped.

50% CPU (just physical cores) is operating on only one patient to completion while the other is still in pre-op. Only one section of time lost to the switch, so ultimately, more work gets done, with less stress (CPU heat) on you.

The hyperthreads don't count in PG primefinding (LLR/GFN) because it is so specialized. Sieving projects are less specialized and work better with 100% CPU enabled.

BTW, since you are probably on a laptop, make sure there is plenty of space around the fans to keep cool air going in unrestricted. You might need to elevate the body off the desk to help with this.
____________
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Message 143090 - Posted: 6 Sep 2020 | 1:10:10 UTC - in response to Message 143070.

Great analogy, thanks.
____________

Joby Kechinsky
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Message 143098 - Posted: 6 Sep 2020 | 5:13:21 UTC - in response to Message 143070.
Last modified: 6 Sep 2020 | 5:55:25 UTC

I have changed the settings to "On multiprocessors, use atmost 50% of the processors", as well as leaving the CPU setting at 100%. While I have seen a reduction in CPU heat, I have not seen any significant increase in the speed -- over 30 minutes my computer averaged 0.449% per task per minute, indicating onebatch of 4 tasks still requires over 3.5 hours to complete. Did I toggle the correct setting? Or are there other settings that I should adjust as well?

Joby Kechinsky
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PPS LLR Silver: Earned 100,000 credits (284,624)SoB LLR Silver: Earned 100,000 credits (389,176)PPS Sieve Silver: Earned 100,000 credits (185,405)GFN Gold: Earned 500,000 credits (598,971)
Message 143104 - Posted: 6 Sep 2020 | 8:34:00 UTC - in response to Message 143070.

Update: I think the settings have just come into effect with the completion of the latest batch of tasks as my computer is now processing 2 tasks at once instead of 4. However the rate of task completion is even slower than before.

Instead of completing one batch of 4 tasks every 3.5 hours, as it was doing previously, one batch of 2 tasks now takes 2 hours to complete, representing a 15% speed reduction...

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Message 143108 - Posted: 6 Sep 2020 | 11:06:34 UTC - in response to Message 143104.

Update: I think the settings have just come into effect with the completion of the latest batch of tasks as my computer is now processing 2 tasks at once instead of 4. However the rate of task completion is even slower than before.

Instead of completing one batch of 4 tasks every 3.5 hours, as it was doing previously, one batch of 2 tasks now takes 2 hours to complete, representing a 15% speed reduction...


You should set it to do one cpu task at a time using 50% of the cpu cores, you can do that in the venue settings for that pc for the LLR tasks. You can set both how many units to run at one time and how many cpu cores to use while running the units.

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Discovered 1 mega primeFound 1 prime in the 2018 Tour de PrimesFound 1 prime in the 2019 Tour de PrimesFound 1 prime in the 2020 Tour de Primes321 LLR Amethyst: Earned 1,000,000 credits (1,029,579)Cullen LLR Amethyst: Earned 1,000,000 credits (1,970,265)ESP LLR Ruby: Earned 2,000,000 credits (2,022,721)Generalized Cullen/Woodall LLR Gold: Earned 500,000 credits (661,578)PPS LLR Jade: Earned 10,000,000 credits (15,775,570)PSP LLR Ruby: Earned 2,000,000 credits (2,255,024)SoB LLR Turquoise: Earned 5,000,000 credits (9,221,370)SR5 LLR Gold: Earned 500,000 credits (500,512)SGS LLR Amethyst: Earned 1,000,000 credits (1,065,013)TRP LLR Ruby: Earned 2,000,000 credits (2,162,752)Woodall LLR Ruby: Earned 2,000,000 credits (2,000,471)321 Sieve (suspended) Ruby: Earned 2,000,000 credits (2,035,186)Generalized Cullen/Woodall Sieve (suspended) Turquoise: Earned 5,000,000 credits (5,002,647)PPS Sieve Sapphire: Earned 20,000,000 credits (46,148,990)TRP Sieve (suspended) Silver: Earned 100,000 credits (156,305)AP 26/27 Ruby: Earned 2,000,000 credits (3,873,194)WW Amethyst: Earned 1,000,000 credits (1,000,000)GFN Double Bronze: Earned 100,000,000 credits (102,553,767)
Message 143109 - Posted: 6 Sep 2020 | 11:39:39 UTC

Hello.
I agree with Pokey to get no more than one task at a time, and set llr multi-threading to two threads for running llr. As you also run sieve tasks, which use one thread each, make that a maximum of two tasks at a time.

Also, if you have a look at the typical run-time when choosing projects from the preferences, you might want to choose only the shorter running ones, as your machine might well take longer for llr than the typical amount of time.
____________
Greetings, Jens

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Message boards : Problems and Help : PPSE tasks taking much longer than expected

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