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by ctz 604 days ago
Note that the AVX-512 code we're referring to is the code that Intel also contributed to OpenSSL.

As a side-note, I believe the CPU we tested this on does not suffer from the AVX-512 power limits reported with earlier AVX-512 parts. https://travisdowns.github.io/blog/2020/08/19/icl-avx512-fre... seems to confirm that.
2 comments
anitil 604 days ago
~That page is the first I've heard of license-based downclocking. I know there's no ethical reason not to do it, and it's similar to fusing a higher/lower performance chip out of the same base design, and free-market etc.

But it just makes me sad.~

Edit: Based of this comment [0] and replies, it appears I've misunderstood what 'license' means. My apologies

[0] https://news.ycombinator.com/item?id=24218310

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cesaref 604 days ago
Ah, ok. So the frequency locking was to reduce jitter on the performance tests? If so, this makes sense.
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carlmr 603 days ago
It's also fairly normal to do this. Google benchmark [1] even warns you about this.

[1] https://github.com/google/benchmark

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rerdavies 603 days ago
Is it really reasonable to lock your TLS web transfer to a specific CPU thread? Not sure it actually does make sense.

Would be nice to see the non-AVX512 results.

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toast0 603 days ago
> Is it really reasonable to lock your TLS web transfer to a specific CPU thread? Not sure it actually does make sense.

Only if you want good performance. If you're doing a lot of networking, you want your userland socket servicing pinned to the same CPU that the kernel is using for that socket. Which is easiest to achieve if you cpu pin nic queues and server threads. (If you want really good performance, you might want to skip userland with sendfile + kTLS or nic TLS, or maybe skip the kernel with userland networking)

For a benchmark, cpu pinning and tight control of the system is a clear prerequisite; you want to maximize repeatability, and user threads bouncing around cpu threads leads to less repeatable results.

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rerdavies 602 days ago
If you really need good performance, aren't you going to be running far more sockets than you have network adapters?
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