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Old 2018-12-12, 17:05   #342
chris2be8
 
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Probably Windows needs ~2-3Gb for itself, regardless of how much ram the system has. So a system with more ram has a larger proportion available for applications to use.

And Windows 10 probably needs more memory than Windows 7.

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Old 2018-12-13, 02:44   #343
kriesel
 
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Quote:
Originally Posted by kriesel View Post
16GB ram on a Windows 10 system, with 2 workers, refused 8000MB, said 7281 max.
7281MB*2/(16*1024) =~0.8888, while 8000MB*2/(16*1024)=~0.9766.
The question remains, why the odd 7281 MB figure?
My bad, remembered the Win10 system wrong, it's 16GB-CAPABLE, 8GB installed currently.
Win10 and the rest of prime95 V29.4b8 including a primality test worker are getting by in the remaining 8192-7281 max=911 MB min. It's currently using 6531 MB of the 7281 MB in a P-1 run.

Last fiddled with by kriesel on 2018-12-13 at 02:47
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Old 2018-12-22, 09:05   #344
theonetruepath
 
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Default CPU usage, Intel i9-7900X @3.3GHz

I'm on Windows 7 Pro. My CPU has 10 physical cores, 20 logical cores and 64GB of ram.

When I run single-threaded programs I can run 20 of them at 'full speed' which is reflected by the CPU usage being shown as 100% in task manager.

When I run Prime95 and set everything as it recommends (and using 32GB of ram) it decides on 6 workers and task manager shows 65% usage, ie 13 threads.

I tried setting number of CPU cores etc in local.txt:
NumCPUs=10
CpuNumHyperthreads=2
CpuSpeed=3300

...makes no difference. If you try to change to 7 workers it grumbles then if you force it, it drops to around 30% CPU usage.

Is there any way to get it to fully utilise the 20 threads?

Also the completion estimates are way, way out. Every minute or so it gives a new estimate for each worker, and that estimate drops by between 7 and 20 minutes each time. Will this be fixed after the program runs a benchmark over the next day or so?
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Old 2018-12-22, 14:20   #345
ATH
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Try with:
WorkerThreads=5
CoresPerTest=2
HyperthreadLL=1

or if you want fewer workers:
WorkerThreads=2
CoresPerTest=5
HyperthreadLL=1

But it might be faster to disable hyperthreading in the BIOS, it is very rare that HT is faster in Prime95 because everything is capped by the RAM speed.

HT is designed for "normal" tasks like browsing, word processing etc. where each thread to not utilize the core fully, so another thread can successfully use it some of the time.

Last fiddled with by ATH on 2018-12-22 at 14:21
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Old 2018-12-22, 15:12   #346
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Quote:
Originally Posted by theonetruepath View Post
I'm on Windows 7 Pro. My CPU has 10 physical cores, 20 logical cores and 64GB of ram.

When I run single-threaded programs I can run 20 of them at 'full speed' which is reflected by the CPU usage being shown as 100% in task manager.

When I run Prime95 and set everything as it recommends (and using 32GB of ram) it decides on 6 workers and task manager shows 65% usage, ie 13 threads.

I tried setting number of CPU cores etc in local.txt:
NumCPUs=10
CpuNumHyperthreads=2
CpuSpeed=3300

...makes no difference. If you try to change to 7 workers it grumbles then if you force it, it drops to around 30% CPU usage.

Is there any way to get it to fully utilise the 20 threads?

Also the completion estimates are way, way out. Every minute or so it gives a new estimate for each worker, and that estimate drops by between 7 and 20 minutes each time. Will this be fixed after the program runs a benchmark over the next day or so?
There are a number of things to consider:
32 vs 64 bit OS, 32 vs 64 bit CPU registers, \(2^{32}\)vs \(2^{64}\) addressable memory locations, memory speed, memory channels, memory bus width, memory rank, instructions per memory clock, and more.

All these go into formulae for theoretical maximum possible operation bandwidth of CPU or Memory.

if Memory burst rate bandwidth is less than CPU output then you are memory bound. at 1 byte per address:

a 32 bit register can only address 4 GiB of memory.
a 64 bit register can address 16 EiB of memory in theory.

if each CPU core (with 1 register for addressing) is working at 3.3 GHz then:

32 bit can put 13.2 GiB into memory per second per core in theory.

64 bit can put 26.4 GiB into memory per second per core in theory.

This all assumes 1 operation per clock. etc.

So without proper information on your setup, people can only guess at possible best throughput scenarios.

Last fiddled with by science_man_88 on 2018-12-22 at 15:40 Reason: typos
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Old 2018-12-22, 15:32   #347
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As ATH said, your system is probably memory bandwidth bound trying to run 10 cores, unless you have DDR4-3200 or higher. If you have stock speed memory at 2666, it's probably no slower to run only 8 cores.

With regards to hyperthreading, it offers almost no benefit and is often a detriment to Prime95. Prime95 is finely tuned assembly capable of saturating a CPU core: it doesn't leave execution gaps that another thread could easily fill.

If it's a desktop system, I would still leave hyperthreading enabled in the BIOS. Prime95 is an excellent way to fill the execution gaps left by desktop apps, and the hyperthreading makes those apps more responsive when running Prime95.
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Old 2018-12-22, 16:14   #348
Prime95
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Quote:
Originally Posted by theonetruepath View Post
I'm on Windows 7 Pro. My CPU has 10 physical cores, 20 logical cores and 64GB of ram.

When I run single-threaded programs I can run 20 of them at 'full speed' which is reflected by the CPU usage being shown as 100% in task manager.
Run version 29.5 -- it makes use of the AVX-512 instructions (about 15% faster). You'll have to dig through the 29.5 thread to find the link to the Windows executable.

Your goal is to get to 50% CPU usage -- hyperthreading will slow down prime95. You can leave hyperthreading on in the BIOS.
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Old 2018-12-22, 16:14   #349
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another thing to point out is there is a difference between multithreading and hyperthreading

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Old 2018-12-22, 18:18   #350
ATH
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If you leave Hyperthreading on like George and Mark suggest then remove the HyperthreadLL=1 line from local.txt or use HyperthreadLL=0.

Then use a combination of WorkerThreads= and CoresPerTest= that multiplies to 10, like 1/10, 2/5, 5/2 or 10/1. Then you have to content with that CPU usage of Prime95 will show as 50% but it will be running as fast as it can. The other 50% is the 10 "virtual" threads 1 for each core that is not currently working, while the other 10 threads are using the 10 cores fully.
Yes it is a stupid system imo as well, CPU usage should show the actually usage of the physical cores not some virtual threads that does not matter...which is why I have disabled HT in my BIOS.

Last fiddled with by ATH on 2018-12-22 at 18:20
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Old 2018-12-22, 23:12   #351
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Quote:
Originally Posted by ATH View Post
But it might be faster to disable hyperthreading in the BIOS, it is very rare that HT is faster in Prime95 because everything is capped by the RAM speed.
If the system is dedicated to Prime95 I would agree. For a system that sees other uses, HT still helps. When I have HT disabled and play a game or encode videos, my ms/iter time in Prime95 goes up by 500-600%. With HT enabled, Prime is only about 10-15% slower on my system when running those tasks.
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Old 2018-12-22, 23:57   #352
chalsall
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Quote:
Originally Posted by NookieN View Post
When I have HT disabled and play a game or encode videos, my ms/iter time in Prime95 goes up by 500-600%.
That's exactly by design. Every other program on your computer gets priority over Prime95.

Quote:
Originally Posted by NookieN View Post
With HT enabled, Prime is only about 10-15% slower on my system when running those tasks.
OK, that suggests your games and your video encoders are not terribly optimized. But an important thing to take into consideration is Prime95 /can/ slow down the responsiveness of your other apps.

Every "use case" is different. Do "what makes sense" for you.
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