Lower power consumption when sieving
 

CPU: Ryzen 9 3900x
RAM: 16 GB DDR4
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?

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.

My guess is that sieving doesn't use the AVX units while LLR does. This has a significant impact on power consumption.

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.

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.