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Old 18th October 2018, 17:24   #6450  |  Link
nevcairiel
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Join Date: Mar 2010
Location: Hamburg/Germany
Posts: 10,342
Quote:
Originally Posted by benwaggoner View Post
Would it be hotter? Or would it just be slower due to thermal throttling.

I wouldn't be surprised if Intel's next big microarchitecture revision makes AVX512 useful in cases where it isn't today. We saw the same thing with Skylake and AVX2.
The real problem with AVX512 is the strong downclock on stock CPUs, and the high density of the AVX512 instructions, causing a high power draw in a small die area.

With overclockable CPUs, you can control the AVX512 offset and make it useful for x265, but on Xeons or the like, you probably don't get that level of control, and the downclock during AVX512 might offset the advantages it offers.

Additionally, x265 is a pretty "light" AVX512 load. If you change the offset for a lower downclock and then run a strong AVX512 load (like pure math, ie. FFTs, for a prolonged time), your system may become unstable, due to the extreme density of all the heat and power draw. So its really hard to balance.
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