I9 with cores and HT off

[dany man]

If I shut off 4 cores and HT on a 9900k would all the L3 still be usable by the other 4 cores and would it free up any OC'ing room?
I was thinking about picking one up for the added L3 but I don't need the extra cores but the added L3 would been nice. But if killing off the other cores does not alow for more OC'ing head room it would be pointless for me as I need the best single core performance with lots a L2/L3. and I seen that most 9900 tops out at 5ghz.

Thanks.

 

[Absalom]

For an i9 9900k, the aggregated L3 cache is usable by any single core via the ringbus. I'm not 100% sure if disabling a core disables its slice of the L3 cache? My guess is that it does not. I don't have an i9 to experiment with, but you can easily verify that with CPU-Z.

Disabling HT just disables a logical CPU. Disabling that logical CPU will simply idle the redundant parts of the physical core used for HT. Whether you net anything from doing that is debatable. It would certainly reduce power consumption, thus heat, assuming there's a significant load. The negative side effects of disabling HT is that you might have a less responsive OS. The same can be said for disabling physical cores.

Unless you have a specific lightly threaded workload that benefits from a large amount of cache, I don't think disabling cores for the purpose of gaining a larger L3 is a worthy trade-off. Addressing L3 via ringbus is going to be slower than anything local, so having a cache miss is going to have to painfully go through the slower ringbus itself. Still better than fetching from RAM or disk obviously. You can overclock the Uncore, thus ringbus, but again, YMMV.

Basically, you want to turn an i9 9900k into a i5 7600k with a larger L3 cache.

 

[dany man]

Basically, you want to turn an i9 9900k into a i5 7600k with a larger L3 cache.

That is what I want.