AVX-512 downclocking post

By: David Kanter (dkanter.delete@this.realworldtech.com), January 18, 2020 10:27 am
Room: Moderated Discussions
anon³ (nope.delete@this.example.test) on January 17, 2020 12:25 am wrote:

> Back on topic: anyone know what happened to AMD's adaptive clocking (as used in Steamroller and described
> on the front page here)? I have seen no marketing material implying that it's in Zen/+/2, but I also haven't
> seen any analysis at this level of detail or finer for Zen. It seems like that scheme or a refined version
> would be a much more effective solution than Intel's brutish mess. A single heavy instruction burning 75,000
> cycles (at 3GHz, 10us halted plus 10us gated down to 1/4 rate) seems... suboptimal.

It's used by Zen and successors. It's also in AMD GPUs now.

It is very elegant, but it is not without cost.

I spoke to a few clocking experts, and it complicates the clocking system a fair bit. Especially for designs that want to hit max frequency.

So it's a pretty good fit for something like a GPU or accelerator that has a lot of dynamic capacitance (read parallelism). It's great for a CPU that doesn't want to hit maximum frequency.

> I'm also a bit surprised at how long the Intel FIVR takes to slew (according to the numbers in
> the other thread plus your measured results). Sure, it's regulating truly massive currents going
> into gigantic capacitances (at least for the time scales involved), but my intuition would have
> been that a >100MHz controller could have done a bit better. But probably that's just me being
> thrown off by recently designing with CFB amplifiers that slew at over 1000V/us....

The FIVR is extremely fast. It's the sensing and control that is the limiting factor for HSW/BDW/SKX generations. The FIVR also improved in ICL, and it stands to reason they improved the sense and control as well.

David
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AVX-512 downclocking postTravis Downs2020/01/16 09:20 PM
  AVX-512 downclocking postanon³2020/01/17 01:25 AM
    AVX-512 downclocking postAndrei2020/01/17 02:47 AM
      AVX-512 downclocking postMontaray Jack2020/01/17 03:58 PM
        AVX-512 downclocking postAndrei2020/01/17 11:40 PM
          AVX-512 downclocking postMontaray Jack2020/01/19 02:10 AM
            AVX-512 downclocking postJan Olšan2020/01/19 01:01 PM
              AVX-512 downclocking postJan Olšan2020/01/19 01:11 PM
    AVX-512 downclocking postTravis Downs2020/01/17 02:59 PM
    AVX-512 downclocking postDavid Kanter2020/01/18 10:27 AM
      magnetic inductorsjokerman2020/01/18 08:03 PM
      AVX-512 downclocking postTravis Downs2020/01/24 11:36 AM
  AVX-512 downclocking postRay2020/01/17 02:22 AM
    AVX-512 downclocking postTravis Downs2020/01/17 01:10 PM
  AVX-512 downclocking postEtienne2020/01/17 03:16 AM
    Thanks, typos fixed and credited (NT)Travis Downs2020/01/17 01:15 PM
  Title suggestions welcome (NT)Travis Downs2020/01/17 08:54 AM
  AVX-512 downclocking postanonymou52020/01/17 10:53 AM
    AVX-512 downclocking postTravis Downs2020/01/17 11:14 AM
      AVX-512 downclocking postYoav2020/01/17 11:50 AM
        AVX-512 downclocking postTravis Downs2020/01/17 01:14 PM
      AVX-512 downclocking postanonymou52020/01/17 04:26 PM
        AVX-512 downclocking postTravis Downs2020/01/22 08:19 PM
          AVX-512 downclocking postanonymou52020/01/23 12:56 AM
            AVX-512 downclocking postFoyle2020/01/23 05:51 AM
              AVX-512 downclocking postanonymou52020/01/23 06:57 AM
                AVX-512 downclocking postTravis Downs2020/01/24 12:49 PM
            finer-grained licensesTravis Downs2020/01/24 01:03 PM
              finer-grained licensesanonymou52020/01/24 04:28 PM
                finer-grained licensesTravis Downs2020/01/25 09:46 AM
  post published (new line)Travis Downs2020/01/17 11:55 AM
    should say: (new LINK) (NT)Travis Downs2020/01/17 11:55 AM
      should say: (new LINK)Tim McCaffrey2020/01/17 01:44 PM
        Thanks, fixed and credited (NT)Travis Downs2020/01/17 02:54 PM
      should say: (new LINK)anon2020/01/17 09:12 PM
        should say: (new LINK)Travis Downs2020/01/22 03:28 PM
          Thanks!anon2020/01/22 08:06 PM
            Thanks!Travis Downs2020/01/22 08:16 PM
              Thanks!anon2020/01/22 10:20 PM
                Thanks!Travis Downs2020/01/23 01:51 AM
                  Thanks!Linus Torvalds2020/01/23 05:33 PM
                    Thanks!Travis Downs2020/01/24 12:44 PM
  Throttling dispatchGabriele Svelto2020/01/22 01:40 PM
    Itanium also used itDavid Kanter2020/01/22 02:04 PM
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