Sunny Cove wide

By: Kevin G (, December 13, 2018 8:37 am
Room: Moderated Discussions
Seni ( on December 13, 2018 2:33 am wrote:
> Travis Downs ( on December 12, 2018 8:25 pm wrote:
> > Seni ( on December 12, 2018 1:58 pm wrote:
> > > -2nd store port. As far as x86 is concerned, this is (probably?) the only increase
> > > in store ports that has ever occurred. It's unclear how important store port count
> > > is to performance, since there is no precedent to base an estimate on.
> > >
> > >
> > > -5-wide renamer. The wording I've seen is extremely vague and possibly misleading, but
> > > it sounds like they increased the renamer from 4 work units to 5. A renamer work unit
> > > is not the same as either an instruction or a uop, though, so a lot unresolved questions
> > > here. There is no sign of a breakthrough renaming technique. Just wider.
> >
> > The work unit is "fused uop". I.e., something like an ALU ok with a memory-source operand
> > counts as 1 for renaming, even though it will execute as two separate (unfused) uops.
> >
> > At least that has been the case going back to at least SNB.
> Are you certain that there have been no changes in the details
> of what can be fused and where the fusion occurs?

The last big change to cracking and fusion was with Nehalem when it began to work in 64 bit mode. Where this occurs at least to that generation was with neighboring instructions in very select (but common) instances. Since then Intel has been rather quiet on these details so the presumption was that they weren't focusing too much on them.

However, there does appear to be a few cases for further improvement. Only one fused op can be used at once in Sandy Bridge and previous designs. Not sure how often two fused ops can appears next to each other but it'd be a minor boost. Intel could expand the window for fusing instructions instead of nearest neighbors. I fathom that this would be rather complex to implement and the power cost may exceed the performance gains it would extract. On Haswell and later, there is the possibility that multiply-add could be fused together. For legacy FP code, this code be a nice big win. Integer multiply-add would be a small but seemingly straight forward boost. Similarly similar scalar FP operations could be merged into a single vector operation for legacy code. This would certainly involve more complexity with the big gains limited to older code. With newer code, there could be incentive to fuse multiple vector operations into a larger vector op (two independent 256 bit vector adds to one 512 bit vector add). Again, complexity/power vs. performance gain it does seem like it would be an immediate win off hand.

> > > -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.
> >
> > It will be interesting to see what they did with the 64 KiB L1 - is
> > it still VIPT, implying 16-way associativity, or something else?
> >
> > >
> > >
> > > -no meaningful info on ooo depth.

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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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