Go Back > Great Internet Mersenne Prime Search > Hardware

Thread Tools
Old 2021-06-12, 06:10   #1
bur's Avatar
Aug 2020

389 Posts
Default Lower power consumption when sieving

CPU: Ryzen 9 3900x
Storage: Samsung 970 Evo
Windows 10

I was doing LLR on the 12 cores for a few months and to keep the room temperature low I throttled PPT to 128 W which kept the core temperature at around 71 °C while decreasing LLR throughput by only 1%.

Recently I switched to sieving with sr1sieve and noticed that the core temperature had dropped to 59 °C. Power consumption is only about 80-90 W. Playing around with PPT doesn't change anything. According to Windows all assigned cores (0,2,4,..,11) are fully utilized.

Is there a bottleneck or does sieving behave like that? I thought it was the other way around. Is the SSD too slow for 12 simultaenous sievings? But taskmanager doesn't show heavy disk activity.

It tests about 31,000,000 p/s per core, is that expected on that CPU?

Last fiddled with by bur on 2021-06-12 at 06:12
bur is offline   Reply With Quote
Old 2021-06-12, 07:29   #2
axn's Avatar
Jun 2003

32×569 Posts

Sieving has lot of memory activities, which means there is some waiting on the CPU for memory. So this is kind of expected.

You can compensate for it somewhat by fully utilizing the SMT (HT in intel) by using all 24 SMT threads. So if you run the sieve with 24 threads, you might get 20-30% thruput increase and probably similar increase in power consumption.
axn is online now   Reply With Quote
Old 2021-06-12, 17:12   #3
ldesnogu's Avatar
Jan 2008

2×52×11 Posts

My guess is that sieving doesn't use the AVX units while LLR does. This has a significant impact on power consumption.
ldesnogu is offline   Reply With Quote
Old 2021-06-13, 05:25   #4
bur's Avatar
Aug 2020

389 Posts

Ok; good thing the HT comes in handy for once. Shouldn't the CPU utilization be below 100%/core then though?

AVX could play a role, too, but 80-90 W is far from what the CPU has as its default long term limit (142 W) and LLR happily used all of that. So I assume it's not the main factor.

Thanks for the advice.
bur is offline   Reply With Quote
Old 2021-06-16, 00:42   #5
Happy5214's Avatar
Nov 2008
The Alamo City

2×373 Posts

The 24 hyperthreads should all be displayed separately as "logical cores", so if it only displays 100% on 0-11, you're not using HT on all 12 cores.
Happy5214 is offline   Reply With Quote

Thread Tools

Similar Threads
Thread Thread Starter Forum Replies Last Post
power consumption esakertt Hardware 1 2012-10-09 20:19
power consumption Unregistered Information & Answers 2 2011-01-27 20:48
Now power consumption numbers using Prime95 Dresdenboy Hardware 1 2004-11-23 18:29
Power consumption dans Hardware 7 2004-06-06 15:15
Power consumption optim Hardware 8 2003-12-06 04:13

All times are UTC. The time now is 17:02.

Tue Sep 21 17:02:36 UTC 2021 up 60 days, 11:31, 0 users, load averages: 2.04, 1.81, 1.65

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, 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.