4 ms·

> I've voiced this before but I think AVX-512 is completely irrelevant in the consumer spac Don’t forget that reviewers made a huge deal out of the fact that C

> I've voiced this before but I think AVX-512 is completely irrelevant in the consumer spac Don’t forget that reviewers made a huge deal out of the fact that CPUs downclock themselves when running AVX instructions. Several reviewers tried to make this into some sort of scandal at the time, which I’d guess contributed to Intel wanting to remove the feature from consumer CPUs. Of course, many of those same reviewers are now capitalizing on Intel removing AVX-512 support while ignoring the fact that you had to disable all of the efficiency cores if you wanted that feature (worsening thermals and performance in non-AVX) workloads.

FrostKiwi 5y ago
> Don’t forget that reviewers made a huge deal out of the fact that CPUs downclock themselves when running AVX instructions. It was and is kinda a huge deal. I followed the development of Corona Renderer for the past decade closely and one reoccuring theme with conflicting evidence was whether the inclusion of AVX was beneficial or detremental to performance due to resulting down clocking on certain platforms. And surprisingly, now quickly looking through the search function, of the corona renderer forum an update apparently even dropped AVX because of better performance. ( https://forum.corona-renderer.com/index.php?topic=33889.msg188021#msg188021 https://forum.corona-renderer.com/index.php?topic=33889.msg1... ) Though I wonder if this is accurate or if the post is missing context...
adgjlsfhk1 5y ago
To me, it does seem really weird that they opted to downclock the entire CPU rather than increase the latency of the instructions that caused overheating. That feels like it would have been a much less disruptive solution that would work strictly better.
- colejohnson66 5y ago
  If you increase latency, the ROB fills up quicker, and could get full which would back up the pipe. It makes sense why they’d choose to use the default “downclock on overheat” rather than add more circuitry to deal with that specific issue.
- BeeOnRope 5y ago
  When the first AVX instruction is run after a long period of no AVX, something like this does happen: the dispatch of instructions is throttled to 1 out of 4 cycles while some AVX instruction is in the scheduler (this applies to all instructions, not just AVX). This is severe restriction: even if could be limited to AVX instructions, running at 25% of the throughput would make AVX pretty useless. This state persists only for a short time until a voltage and possibly frequency transition can be made at which point everything can run at full speed (albeit sometimes at a reduce frequency).

FrostKiwi 5y ago

> Don’t forget that reviewers made a huge deal out of the fact that CPUs downclock themselves when running AVX instructions. It was and is kinda a huge deal. I followed the development of Corona Renderer for the past decade closely and one reoccuring theme with conflicting evidence was whether the inclusion of AVX was beneficial or detremental to performance due to resulting down clocking on certain platforms. And surprisingly, now quickly looking through the search function, of the corona renderer forum an update apparently even dropped AVX because of better performance. ( https://forum.corona-renderer.com/index.php?topic=33889.msg188021#msg188021 https://forum.corona-renderer.com/index.php?topic=33889.msg1... ) Though I wonder if this is accurate or if the post is missing context...

adgjlsfhk1 5y ago

To me, it does seem really weird that they opted to downclock the entire CPU rather than increase the latency of the instructions that caused overheating. That feels like it would have been a much less disruptive solution that would work strictly better.

colejohnson66 5y ago
If you increase latency, the ROB fills up quicker, and could get full which would back up the pipe. It makes sense why they’d choose to use the default “downclock on overheat” rather than add more circuitry to deal with that specific issue.
BeeOnRope 5y ago
When the first AVX instruction is run after a long period of no AVX, something like this does happen: the dispatch of instructions is throttled to 1 out of 4 cycles while some AVX instruction is in the scheduler (this applies to all instructions, not just AVX). This is severe restriction: even if could be limited to AVX instructions, running at 25% of the throughput would make AVX pretty useless. This state persists only for a short time until a voltage and possibly frequency transition can be made at which point everything can run at full speed (albeit sometimes at a reduce frequency).