Sunny Cove wide

By: Travis Downs (travis.downs.delete@this.gmail.com), December 13, 2018 9:39 am
Room: Moderated Discussions
anon (spam.delete.delete.delete@this.this.this.spam.com) on December 13, 2018 8:06 am wrote:
> -.- (blarg.delete@this.mailinator.com) on December 13, 2018 3:37 am wrote:
> > Seni (seniike.delete@this.hotmail.com) on December 12, 2018 1:58 pm wrote:
> > > -several signs point to moderately lower clock frequency than Skylake family. The renamer is one, but
> > > also the enlarged caches (L1, uop cache and tlb), the dual store port LSU, and a few other areas.
> >
> > I'm a little curious about the AVX-512 units on Sunny Cove.
> > Skylake has 2x 512b units, where ports 0 and 1 combine to form one unit. To accommodate
> > this, Skylake made supported vector operations on these ports largely the same. Also,
> > instructions execute on port 0, only borrowing the vector unit of port 1.
> >
> > Sunny Cove adds vector shuffle to port 1, which means that port 0 and 1 now support different
> > vector instructions. Curious to note that this is port 1 and not 0, which would be the logical
> > place to put it if it had 2x 512b units. Also, I suspect that permutes (assuming 'shuffle' includes
> > cross-lane permutes) are probably best done on units which have the full width, rather than trying
> > to split the instruction into halves and dealing with the the complexity of such.
> >
> > So perhaps this means...
> >
> > - port 1 remains 256b, and the shuffle unit can only do 256b shuffles, meaning
> > the CPU can do either 2x 256b (port 1+5) or 1x 512b (port 5 only) per clock?
> > - port 1 is extended to 512b, suggesting that port 0 is also, so the CPU has 3x 512b ports and can do
> > 3x 512b FMA per cycle? (assuming non-'gimped' AVX-512 CPUs like the single port AVX-512 Skylakes)
> > - some other scheme, like 256b port 1 but a 512b shuffle unit (not
> > clued enough on CPU design to know the feasibility of this)?
> >
> > What do you think?
> > 3x 512b units seems the most likely to me - gives more FLOPS, which Intel likes, but the power usage...
>
> Keep in mind that the ports do not necessarily need to support the
> same uops for 256b and 512b. Port 5 doesn't do 256b FMA iirc.
> So both 256b shuffle on port 1, but no 512b shuffle on port 0 and 256b shuffle on port 1, 512b
> shuffle on port 0 (which reuses the same unit and it's simply on port 1 for 256b because div
> is already on port 0), but no 256b shuffle on port 0 are equally possible and plausible.
> 3x 512b shuffle seems unlikely and throwing in FMA as well is
> even more unlikely since the two are not exactly related.

If I understood the suggested possibility, it was 3 512b units but only 2 512b shuffles (p1 and p5).

>
> Either way two shuffle ports are nice to have. Even if they are not 512b it's
> still nice getting the same throughput with 256b without having to use AVX512
> or getting a massive boost when you actually want independent 256b shuffles.

Definitely. It's been a decade of writing code that uses more blends but fewer shuffles or whatever to get around p5 shuffle pressure. This would provide a nice boost to a lot of those things (after a re-write though!).

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TopicPosted ByDate
Sunny Cove wideSeni2018/12/12 02:58 PM
  Sunny Cove wideTravis Downs2018/12/12 09:25 PM
    Sunny Cove wideJeff S.2018/12/12 10:26 PM
      Sunny Cove wideTravis Downs2018/12/13 08:42 AM
        Sunny Cove wideanon2018/12/13 09:09 AM
          Sunny Cove wideTravis Downs2018/12/13 09:30 AM
            Sunny Cove wideJeff S.2018/12/13 09:40 AM
              Sunny Cove wideTravis Downs2018/12/13 09:55 AM
                Sunny Cove wideJeff S.2018/12/13 12:41 PM
                  Sunny Cove wideTravis Downs2018/12/13 02:03 PM
                  Non-power-of-two set sizesPaul A. Clayton2018/12/15 07:30 PM
        Sunny Cove wideJeff S.2018/12/13 09:33 AM
          Sunny Cove wideTravis Downs2018/12/13 09:50 AM
          What is "u-tagged"?G Adair2018/12/13 09:54 PM
            What is "u-tagged"?Travis Downs2018/12/13 11:22 PM
            What is "u-tagged"?Jeff S.2018/12/14 08:48 AM
              What is "u-tagged"?anon2018/12/14 08:51 PM
                What is "u-tagged"?Jeff S.2018/12/14 10:23 PM
                  What is "u-tagged"?anon2018/12/15 05:37 AM
                    What is "u-tagged"?anon2018/12/15 08:06 AM
                      What is "u-tagged"?Travis Downs2018/12/15 09:52 AM
                        What is "u-tagged"?anon2018/12/16 08:26 AM
                          What is "u-tagged"?Anon2018/12/18 04:25 AM
    Sunny Cove wideSeni2018/12/13 03:33 AM
      Sunny Cove wideKevin G2018/12/13 08:37 AM
        Sunny Cove wideTravis Downs2018/12/13 09:17 AM
          Sunny Cove wideKevin G2018/12/17 10:09 AM
            Sunny Cove wideTravis Downs2018/12/18 03:14 PM
              Sunny Cove wideKevin G2018/12/19 12:02 PM
      Sunny Cove wideTravis Downs2018/12/13 08:51 AM
        Sunny Cove wideMaynard Handley2018/12/13 11:25 AM
          Sunny Cove wideTravis Downs2018/12/13 12:23 PM
            Sunny Cove wideanon2018/12/13 02:01 PM
              Sunny Cove wideTravis Downs2018/12/13 02:22 PM
                Sunny Cove wideanon2018/12/13 04:51 PM
                  Sunny Cove wideTravis Downs2018/12/13 05:36 PM
                    Sunny Cove wideanon2018/12/14 03:57 AM
                      Sunny Cove wideLinus Torvalds2018/12/14 01:54 PM
                        Sunny Cove wideanon2018/12/14 04:25 PM
                          Sunny Cove wideLinus Torvalds2018/12/14 06:46 PM
                            Sunny Cove wideanon2018/12/15 02:57 AM
                              Sunny Cove wideanon2018/12/15 05:59 AM
                                Sunny Cove wideanon2018/12/15 06:59 AM
                                  Sunny Cove wideanon2018/12/15 07:03 AM
                                Sunny Cove widea_different_anon2018/12/15 07:45 AM
                              Sunny Cove wideSeni2018/12/15 06:25 AM
                                Sunny Cove wideanon2018/12/15 07:02 AM
                                  Sunny Cove wideLinus Torvalds2018/12/15 10:52 AM
                                    Sunny Cove wideanon2018/12/15 11:13 AM
                                      Sunny Cove wideTravis Downs2018/12/16 11:15 AM
                                      Sunny Cove wideanon2018/12/17 12:42 AM
                                        how many anons here? (NT)Michael S2018/12/17 02:46 AM
                      Sunny Cove wideTravis Downs2018/12/15 10:08 AM
                        Sunny Cove wideanon2018/12/15 10:55 AM
                          Sunny Cove wideTravis Downs2018/12/16 09:19 AM
                            Sunny Cove wideanon2018/12/16 10:37 AM
                              Sunny Cove wideTravis Downs2018/12/16 10:57 AM
                                Sunny Cove wideanon2018/12/16 12:04 PM
                                  Sunny Cove wideTravis Downs2018/12/16 07:51 PM
                          Sunny Cove wideTravis Downs2018/12/16 11:32 AM
        Sunny Cove wideSeni2018/12/13 04:20 PM
          Fair enough! (NT)Travis Downs2018/12/13 04:43 PM
  Sunny Cove wide-.-2018/12/13 04:37 AM
    Sunny Cove wideanon2018/12/13 09:06 AM
      Sunny Cove wideTravis Downs2018/12/13 09:39 AM
        Sunny Cove wideanon2018/12/13 12:09 PM
          Sunny Cove wideTravis Downs2018/12/13 12:27 PM
            Sunny Cove wideanon2018/12/13 01:11 PM
    Sunny Cove wideTravis Downs2018/12/13 09:23 AM
      Sunny Cove wideanonymous22018/12/13 03:20 PM
        Sunny Cove wideTravis Downs2018/12/13 05:00 PM
          Sunny Cove wideanon³2018/12/13 10:34 PM
            Sunny Cove wideTravis Downs2018/12/16 07:53 PM
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