12:30 "[ISA] do not matter very much"

By: anon2 (anon.delete@this.anon.com), February 22, 2021 8:17 pm
Room: Moderated Discussions
blaine (myname.delete@this.acm.org) on February 22, 2021 9:37 am wrote:
> anon2 (anon.delete@this.anon.com) on February 21, 2021 10:25 pm wrote:
> > Moritz (better.delete@this.not.tell) on February 20, 2021 9:45 am wrote:
> > > 12:30 "[ISA] do not matter very much"
> >
> > First Andy Glew and now Jim Keller?! In light of this new information,
> > my worldview needs revising: clearly these guys are morons.
> >
> > Is there truly not one reputable twitter-based CPU design expert who can
> > see it upon themselves to comfort me and set these two hacks straight?!?
>
> Well I can think of at least one area where a little complexity would be worth it to reduce SW complexity.
> Optimal memcpy is often different between multiple implementations of the same ISA.

Optimal-many-things are often different between multiple implementations of the same ISA, as well as otherwise identical implementations with an ISA difference.

That's one problem, improved (but probably never really solved) with processor designs like OOOE, instructions, and some toolchain techniques.

I don't think memcpy, memset instructions are bad per se, though I still don't understand the fascination with them, unless their proponents are going to move on to do-daxpy, route-ip-packet, gzip-memory, etc instructions when/if one day Intel's rep ; mov finally doesn't suck. But I digress, the point was not a totally open-ended "ISA does not matter".

>
> I would repeat the caveat that instruction sets should give thought to code generation in compilers.
>
> Blasphemy ==> religion rather than reason.
>

In context, Keller clearly did not intend that you could implement a literal 386/87 CPU today that's competitve with M1, or x86 GPUs are right around the corner.

It's that in the context of RISC vs CISC, and that includes the key property of ISAs of how amenable they are to being extended as necessary, that between modern implementations, their ISA differences, for "general purpose", just don't matter that much even the "bad" variable length complex encoding x86. Presumably this also includes the fact that if longer vectors or string instructions or conditional branches or hypervisor extensions or whatever become important, then it has been and will continue to be quite feasible to fit those to existing ISAs.
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TopicPosted ByDate
New Lex Fridman interview with Jim KellerJohnG2021/02/20 12:25 AM
  12:30 "[ISA] do not matter very much" (NT)Moritz2021/02/20 10:45 AM
    AAARGH, what are we going to argue about then? (NT)j2021/02/20 03:43 PM
    Blasphemy! (NT):]2021/02/21 05:49 AM
    12:30 "[ISA] do not matter very much"anon22021/02/21 11:25 PM
      12:30 "[ISA] do not matter very much"Brett2021/02/22 12:59 AM
        12:30 "[ISA] do not matter very much"Etienne Lorrain2021/02/22 02:17 AM
      12:30 "[ISA] do not matter very much"Dummond D. Slow2021/02/22 09:57 AM
        12:30 "[ISA] do not matter very much"Anon2021/02/22 11:52 AM
          12:30 "[ISA] do not matter very much"juanrga2021/02/22 12:01 PM
          12:30 "[ISA] do not matter very much"Mark Roulo2021/02/22 12:54 PM
          ARM being a good idea doesn't mean it would have worked for AMDDummond D. Slow2021/02/22 02:34 PM
            ARM being a good idea doesn't mean it would have worked for AMDAnon2021/02/22 04:25 PM
              ARM being a good idea doesn't mean it would have worked for AMDDummond D. Slow2021/02/22 05:55 PM
                ARM being a good idea doesn't mean it would have worked for AMDDoug S2021/02/23 01:03 PM
                  ARM being a good idea doesn't mean it would have worked for AMDDummond D. Slow2021/02/23 01:27 PM
                    ARM being a good idea doesn't mean it would have worked for AMDBrett2021/02/23 04:57 PM
                      3rd parties licensing ARM coresAnon2021/02/25 05:01 AM
                        3rd parties licensing ARM coresAnon2021/02/25 05:48 AM
                        3rd parties licensing ARM coresdmcq2021/02/25 07:01 AM
                          3rd parties licensing ARM coresDummond D. Slow2021/02/25 10:17 AM
                            3rd parties licensing ARM coresAnon2021/02/25 11:11 AM
                              3rd parties licensing ARM coresAnon2021/02/26 03:54 AM
                              3rd parties licensing ARM coresDummond D. Slow2021/02/26 11:01 AM
            ARM being a good idea doesn't mean it would have worked for AMDLinus Torvalds2021/02/22 06:06 PM
              ARM being a good idea doesn't mean it would have worked for AMDDummond D. Slow2021/02/22 08:19 PM
              ARM being a good idea doesn't mean it would have worked for AMDanon22021/02/22 08:28 PM
              ARM being a good idea doesn't mean it would have worked for AMDdmcq2021/02/23 06:35 AM
                ARM being a good idea doesn't mean it would have worked for AMDJukka Larja2021/02/23 08:12 AM
                  ARM being a good idea doesn't mean it would have worked for AMDSimon Farnsworth2021/02/23 09:42 AM
                    ARM being a good idea doesn't mean it would have worked for AMDJukka Larja2021/02/24 07:03 AM
                ARM may have been a threat to Intelwumpus2021/02/23 09:30 AM
      12:30 "[ISA] do not matter very much"blaine2021/02/22 10:37 AM
        12:30 "[ISA] do not matter very much"anon22021/02/22 08:17 PM
          12:30 "[ISA] do not matter very much"Anon2021/02/23 04:05 AM
            12:30 "[ISA] do not matter very much"Wilco2021/02/23 04:48 AM
              12:30 "[ISA] do not matter very much"Bigos2021/02/23 04:55 AM
                12:30 "[ISA] do not matter very much"Wilco2021/02/23 05:15 AM
                  12:30 "[ISA] do not matter very much"Bigos2021/02/23 06:16 AM
                12:30 "[ISA] do not matter very much"Travis Downs2021/02/27 12:46 AM
              12:30 "[ISA] do not matter very much"Anon2021/02/23 07:26 AM
                12:30 "[ISA] do not matter very much"anon22021/02/23 05:35 PM
                  12:30 "[ISA] do not matter very much"Anon2021/02/24 08:57 AM
                12:30 "[ISA] do not matter very much"Wilco2021/02/24 05:37 AM
                  12:30 "[ISA] do not matter very much"Etienne Lorrain2021/02/24 07:24 AM
                    12:30 "[ISA] do not matter very much"Anon2021/02/24 09:11 AM
                    12:30 "[ISA] do not matter very much"rwessel2021/02/24 09:45 AM
                      12:30 "[ISA] do not matter very much"Etienne Lorrain2021/02/25 02:02 AM
                        12:30 "[ISA] do not matter very much"rwessel2021/02/25 05:51 AM
                        12:30 "[ISA] do not matter very much"Anon2021/02/25 05:53 AM
                  12:30 "[ISA] do not matter very much"Anon2021/02/24 09:07 AM
                    12:30 "[ISA] do not matter very much"Wilco2021/02/24 12:37 PM
                      runtime selection vs. heterogenous cores?Matt Sayler2021/02/24 07:10 PM
                        runtime selection vs. heterogenous cores?Wilco2021/02/26 06:22 AM
            12:30 "[ISA] do not matter very much"anon22021/02/23 05:20 AM
              12:30 "[ISA] do not matter very much"Anon2021/02/23 07:21 AM
                12:30 "[ISA] do not matter very much"none2021/02/23 08:37 AM
                  12:30 "[ISA] do not matter very much"rwessel2021/02/23 10:44 AM
                    12:30 "[ISA] do not matter very much"anon22021/02/23 05:30 PM
                      12:30 "[ISA] do not matter very much"Anon2021/02/24 09:25 AM
                        12:30 "[ISA] do not matter very much"anon.12021/02/25 07:13 AM
                  12:30 "[ISA] do not matter very much"Anon2021/02/24 09:44 AM
                12:30 "[ISA] do not matter very much"anon22021/02/23 04:51 PM
                  12:30 "[ISA] do not matter very much"Anon2021/02/24 09:31 AM
            12:30 "[ISA] do not matter very much"vvid2021/02/23 07:41 AM
              12:30 "[ISA] do not matter very much"Michael S2021/02/23 09:52 AM
                12:30 "[ISA] do not matter very much"rwessel2021/02/23 10:33 AM
                  12:30 "[ISA] do not matter very much"Linus Torvalds2021/02/23 12:44 PM
                    12:30 "[ISA] do not matter very much"rwessel2021/02/23 01:21 PM
                      12:30 "[ISA] do not matter very much"Linus Torvalds2021/02/23 01:30 PM
                        12:30 "[ISA] do not matter very much"Andrey2021/02/25 04:06 AM
                          12:30 "[ISA] do not matter very much"Anon2021/02/25 06:04 AM
                            12:30 "[ISA] do not matter very much"Andrey2021/02/25 06:54 AM
                              12:30 "[ISA] do not matter very much"Anon2021/02/25 07:33 AM
                          12:30 "[ISA] do not matter very much"Linus Torvalds2021/02/25 11:35 AM
                            12:30 "[ISA] do not matter very much"Andrey2021/02/25 02:34 PM
                              12:30 "[ISA] do not matter very much"Etienne Lorrain2021/02/26 02:18 AM
                              12:30 "[ISA] do not matter very much"dmcq2021/02/26 04:23 PM
                12:30 "[ISA] do not matter very much"Anon2021/02/24 09:45 AM
              12:30 "[ISA] do not matter very much"Gabriele Svelto2021/02/23 10:15 AM
          Context of ISA doesn't matterPaul A. Clayton2021/02/26 01:03 PM
  Is there a text version? (NT)Foo_2021/02/20 05:33 PM
    good question (NT)Michael S2021/02/21 05:31 AM
    Is there a text version?:]2021/02/21 11:34 AM
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