# Efficiency: single or multiple projects?



## DSA101 (Nov 24, 2017)

Is it more efficient to crunch a single project on all cores/threads, so all threads can better benefit from the cache, or crunching multiple projects doesn't reduce the real world efficiency much?

Related question. Does hyper threading really help, or it's better to turn it off, so one physical core gets one work unit vs two threads with two work units competing for the same physical core?


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## thebluebumblebee (Dec 20, 2017)

HT does help.

I would think that running one project would be better than switching between projects.


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## Sasqui (Dec 21, 2017)

thebluebumblebee said:


> HT does help.



That's an understatement, at least in other applications I tested a while ago.  One HT core is roughly 90%-95% as efficient as a single physical core.  So two HT cores give about 185% more than one physical core.  If I had the ability at the moment, I'd give cinebench a whirl with and without HT on and show some real numbers.  But alas, I'm here at work where I can only dream about doing that.


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## thebluebumblebee (Dec 21, 2017)

Sasqui said:


> One HT core is roughly 95% as efficient as a single physical core


It's not that good in WCG.  Somewhere between 30-50% more PPD over a non-HT CPU.


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