finer-grained licenses

By: Travis Downs (, January 25, 2020 9:46 am
Room: Moderated Discussions
anonymou5 ( on January 24, 2020 3:28 pm wrote:
> > > 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)
> >
> > Very interesting! So the theory would be these are finer grained levels within each larger license category.
> >
> > Can you figure out how the levels are encoded? That is, is only 1 bit set at once, or within
> > a level is it encoded in binary, e.g., L0 could actually have 2^8 levels? I guess you could
> > check by seeing if the count for umask=0x1 plus umask=0x2 sums to the same as the count for
> > umask=0x3 (the same indicates it is 1-hot, otherwise seems like maybe binary encoding).
> >
> > Intuitively it makes sense that L0 has more levels, because there are probably more
> > opportunities for finer-grained power savings for very low power workloads, perhaps
> > things like a pause loop, or things that don't even use the 128-bit regs, while the
> > other levels have a pretty solid floor on the current because they support wide SIMD.
> my explanation probably wasn't clear enough
> yes, the umask bits do seem to be functional individually i.e. if I set them one by one
> instead of using the documented LVLn values, the counter nicely matches e.g. light/heavy

Thanks. I am modifying the test harness to report these values to see if I can see any correlation.

> > > 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
> >
> > Well yeah, imagine trying to explain 5 levels... 3 is bad enough. The sub-levels
> > are probably mostly invisible since they only involve voltage changes.

It's an interesting paper, but should I be looking at anything specific? I didn't quite catch the relevance (except to prove that yes, di/dt events are a thing and there are specific analog ways of mitigating them: this certainly doesn't exclude other ways like dispatch throttling: I guess they are complementary).

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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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