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What are the net results/consequences to core parking? As in -- aside from potential power savings, why would one want to have core parking enabled (or disabled)?

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up vote 4 down vote accepted

Normally in a hyperthreaded CPU the on-core cache is shared between the two threads that the core supports.

The main gain for core parking is that when the system is not heavily multi-tasking the hyperthreaded cores can be parked, this allows the CPU to reallocate the entire cache on each core to 1 thread instead of 2.

What this should mean is that under low active thread counts the computer (such as you would find while playing a game) the actual performance for those threads is higher because they have a larger on-CPU cache.

Multithreaded applications tend to be large data processing applications so the hit from loosing cache is generally compensated by higher availability of processing power when the cores are unparked.

To an extent this is one of those 'best of both worlds' type things, you gain speed when the system is running just a few heavy threads and gain processing power in multi threaded applications.

What you loose by disabling core parking is the extra performance afforded by a single threaded application having a larger on-CPU cache.

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Ah, interesting. So is it basically "snake oil" voodoo that disabling core parking will bring about gains in performance, particularly, eliminating micro-stutter (in games, for example)? – Coldblackice Mar 20 '13 at 2:41
I didn't know about the link to micro-stuttering until you mentioned it. My best guess though would be that there is something marginal in the system causing the cores to be aggressively parked then unparked causing a performance loss. It could be a bug in the game (not optimized for hyperthreading etc), some driver software, Windows or even a small implementation bug. It sounds like it helps some people but not others which is what makes me think it is system/game related but I can see a situation where it might hurt performance. I'd be surprised if this was the norm though. – Mokubai Mar 20 '13 at 5:34
Gotcha. Much obliged! – Coldblackice Mar 25 '13 at 5:04
Disabling core parking does help some people.… – Moab Jan 8 at 18:14
@Moab Most of the comments I can see that are on-topic and not wandering off into cloud cuckoo land are stating that it is utter bunk and basically placebo. One person did some benchmarks and AFAICT there's no difference.… On my fresh install on Win10 core parking seems to be disabled anyway. I did mention I had seen some people claiming it helped, but can you show any evidence that it is still actively harmful? – Mokubai Jan 8 at 18:28

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