mersenneforum.org  

Go Back   mersenneforum.org > Great Internet Mersenne Prime Search > Hardware

Reply
 
Thread Tools
Old 2016-01-21, 07:43   #1
Ammonia
 
Jan 2016

1 Posts
Default Low clock speeds on Mersenne Prime search

I'm new to this, just downloaded the software a few hours ago and thought I'd try looking for some primes! I have a 12-core Intel Xeon E5-2690v3 with a rated clock speed of 2.6 GHz. I set up 10 workers on 10 CPUs (multithread), allocated 16 GB.

The problem is, when the software is running all the cores are running at a rather low clock speed of 1.8 GHz max. When I use the same software but run the benchmark instead, I get 2.8-2.9 GHz on all cores (stable, over days).

Power saving options for the CPU is turned off, there are no thermal throttling.

Anyone able to help me with the settings to fix this? Or is this normal?
Ammonia is offline   Reply With Quote
Old 2016-01-21, 09:22   #2
0PolarBearsHere
 
0PolarBearsHere's Avatar
 
Oct 2015

26610 Posts
Default

Quote:
Originally Posted by Ammonia View Post
I'm new to this, just downloaded the software a few hours ago and thought I'd try looking for some primes! I have a 12-core Intel Xeon E5-2690v3 with a rated clock speed of 2.6 GHz. I set up 10 workers on 10 CPUs (multithread), allocated 16 GB.

The problem is, when the software is running all the cores are running at a rather low clock speed of 1.8 GHz max. When I use the same software but run the benchmark instead, I get 2.8-2.9 GHz on all cores (stable, over days).

Power saving options for the CPU is turned off, there are no thermal throttling.

Anyone able to help me with the settings to fix this? Or is this normal?
Prime95 sees each "threadable core" as a logical CPU. With your 12 cores and hyper threading, Prime95 should see 24 "cpus" (check in the test->worker windows option, and look at the CPU affinity drop down to confirm). If you want 10 workers to run two threads (i.e. 10 multithreaded workers), you'll need to go through your workers and set each to use 2 CPUs.

Let us know if that doesn't work, or if you don't see the 24 "CPUs" in the affinity dropdown.

Last fiddled with by 0PolarBearsHere on 2016-01-21 at 10:05
0PolarBearsHere is offline   Reply With Quote
Old 2016-01-21, 17:46   #3
Madpoo
Serpentine Vermin Jar
 
Madpoo's Avatar
 
Jul 2014

2·1,637 Posts
Default

Quote:
Originally Posted by Ammonia View Post
I'm new to this, just downloaded the software a few hours ago and thought I'd try looking for some primes! I have a 12-core Intel Xeon E5-2690v3 with a rated clock speed of 2.6 GHz. I set up 10 workers on 10 CPUs (multithread), allocated 16 GB.

The problem is, when the software is running all the cores are running at a rather low clock speed of 1.8 GHz max. When I use the same software but run the benchmark instead, I get 2.8-2.9 GHz on all cores (stable, over days).

Power saving options for the CPU is turned off, there are no thermal throttling.

Anyone able to help me with the settings to fix this? Or is this normal?
I've run it on a system with dual 14-core Xeon E5-2697 v3 and it behaves well, with an appropriate turbo clock speed.

One thing to be aware of is that you might get better overall performance by using a single worker per physical chip, with multiple cores assigned to that single worker.

For my dual socket systems, I run 2 workers, with each worker using all of the physical cores on that chip.

Also as the other reply noted, you will not get any extra benefit from the hyperthreaded cores since there's only one floating point/AVX2 unit per physical core (the HT core can really only pipeline certain integer operations, more or less).

I've spent a lot of time fine-tuning the options of Prime95 to the point where I manually tell it which cores to use, making sure to skip the hyperthread cores. Prime95 generally does a decent job of figuring out which cores are hyperthreaded and will set things up to work optimally, but it could do it better for sure, using modern OS calls directly rather than base it on timing methods. Oh well. I just choose to avoid the ambiguity and set it manually... if you search on this forum you'll find my posts on the topic. Just look for the text "AffinityScramble2".

I probably digressed quite a bit there... your issue was that you aren't seeing your CPUs running at full clock speed. You say there's no thermal throttling going on. Does your system have any power caps, or have you checked your BIOS settings to make sure it's set to high performance? Windows can also override things with the power settings (forcing it into lower power modes).

On my systems, they're servers with real workloads so I have them set to high-performance mode, meaning they're locked at the highest clock speed. If your BIOS supports an option like that, enable it and take a look at CPU-Z or some other utility to see if it's running at the rated (or higher, with turbo modes) clock speeds all the time, even when the system isn't doing much.

The nice thing is that running in high perf mode doesn't use too much more power when the system is idle, but also makes the system really responsive when you do throw a CPU load at it. You don't see weird things with the c-states flicking around all the time.
Madpoo is offline   Reply With Quote
Reply

Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Search for prime Gaussian-Mersenne norms (and G-M-cofactors) Cruelty Proth Prime Search 158 2020-07-31 22:23
Any news about Double Mersenne factor search? biwema Operazione Doppi Mersennes 100 2018-10-01 11:45
New PC dedicated to Mersenne Prime Search Taiy Hardware 12 2018-01-02 15:54
Can I specify the range to search the Mersenne Prime? Unregistered Information & Answers 22 2012-03-20 11:38
Prime Time Clock Jeff Gilchrist Lounge 2 2005-07-15 05:42

All times are UTC. The time now is 16:49.

Tue Aug 11 16:49:35 UTC 2020 up 25 days, 12:36, 1 user, load averages: 1.35, 1.57, 1.55

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.

This forum has received and complied with 0 (zero) government requests for information.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.
A copy of the license is included in the FAQ.