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Old 2010-08-02, 13:55   #9
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Jun 2010

16378 Posts

Originally Posted by mdettweiler View Post
As George suggested earlier, if you can spare it, 500MB is a good minimum amount to allot for P-1. Beyond that point adding more still helps, though it's around there that the returns begin to diminish rather quickly. Note that the full RAM allotment is only used during P-1 stage 2--everything else (including the LL test itself and any TF) uses a minimal amount of RAM (a few MB) because it doesn't need any more than that. So if having 500MB less RAM for a few days at the beginning of some LL tests is not going to severely impact performance on your computer, I'd definitely go for it.

Thank you! I increased the RAM to 500MB, and immediately the "Chance of finding a factor" estimate jumped from the original 3.22% to 5.97%.

Originally Posted by mdettweiler View Post
My guess is that the hit is due to the slight CPU overhead created by normal use of the computer (if you had a web browser open with a few tabs or maybe a webmail interface, that would do it). When you only have one worker going, the other core is completely idle--which means that the operating system's scheduler puts any additional requests for CPU time (web browser, etc.) onto the idle core, leaving the worker all to itself on one core. But when you start the second worker, both cores are filled, which means that the scheduler has got to arbitrarily choose which core to send additional time requests to--which can mean one core or the other at any given moment. The unlucky core then takes a bit of a performance hit on Prime95.

Disclaimer: this is just a hypothesis. I could be completely off-base.
The odd thing is, there were no changes in the way the PC was being used, other than adding the second worker. No programs that wouldn't already be running have been opened. (None that I specifically launched, at any rate.)

Anyway, as you pointed out it's not a big hit. Mostly I'm curious as to how this all works. Thanks for filling me in.

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