AVX-512 downclocking post

By: anonymou5 (no.delete@this.spam.com), January 23, 2020 12:56 am
Room: Moderated Discussions
> > > > When playing with this on SKX, the 3 frequency levels are fairly obvious, but I think I
> > > > can also see evidence for voltage not mapping 1:1, i.e. the result is >3 total, sort of.
> > >
> > > You mean you see more than three distinct voltage levels, right?
> >
> > not quite
> >
> > yes, there are many voltage levels
> >
> > what I seem to see is that within the 3 frequency levels, more seems to be going on
> >
> > it's as if they have sub-levels of some sort
> You see more than 3 frequency levels, or you are seeing more than one voltage per frequency level?
> I also see more than one voltage per frequency level, although the "zoomed in"
> plots may not show it. I am not sure what triggers other voltage transitions.

hah, I think I found a good clue!

look at the CORE_POWER performance counter event (0x28)

the SDM lists it as CORE_POWER.LVLn_TURBO_LICENSE with n={0,1,2}

n=0 for non-AVX, SSE, AVX128, and low-current AVX256
n=1 for high-current AVX256 and low-current AVX512
n=3 for high-current AVX512

basically, the 3 documented turbo frequency curves, as expected

now look at the 3 corresponding umask values (0x07, 0x18, 0x20)

3 bits for n=0
2 bits for n=1
1 bit for n=2

6 bits total

if I try those umask bits *individually*, then I see two behaviors

on SKL, I get counter increments for bits 0, 1, etc. (though not the top ones of course)

on SKX, I get counter increments for bits 1 to 5, but not for bit 0 (I don't know why)

so yeah, on SKX both LVL0 and LVL1 do indeed have 2 sub levels each, for a total of 5

mapping those 5 levels to only 3 frequency curves is a simplification on Intel's part

next: try different SKX microcodes, to see if SKX erratum 101 shows up in all of this...
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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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