New Article: ARM Goes 64-bit

Article: ARM Goes 64-bit
By: David Kanter (dkanter.delete@this.realworldtech.com), November 21, 2012 10:12 am
Room: Moderated Discussions
Wilco (Wilco.Dijkstra.delete@this.ntlworld.com) on November 21, 2012 6:41 am wrote:
> David Kanter (dkanter.delete@this.realworldtech.com) on November 20, 2012 11:07 pm wrote:
> > Rohit (a.delete@this.b.c) on November 20, 2012 4:48 pm wrote:
> > > David Kanter (dkanter.delete@this.realworldtech.com) on November 19, 2012 3:40 pm wrote:
> > > > That's probably a common view. However, there are a number of optimizations that can net
> > > > you huge performance gains and are only viable for JIT systems. I agree you want to do
> > > > as much as possible in your compiler, but somethings require dynamic information.
> > > >
> > > > DK
> > >
> > > Which optimizations are these?
> >
> > Speculative multi-threading using a JIT.
>
> That's not at all JIT related. Has anyone ever shown a speedup using software-only speculation?

Yes, albeit only small ones.

> Automatic multihreading ARMs have been studied for many years. However even with special hardware
> support to detect conflicts, fast rollbacks and spawning threads to different cores it never
> seemed worth the relatively small speedups, especially not when you consider the extra power
> for speculating. The big speedups were all in loops which can be dealt with normally.

Apparently they were studied poorly. I can tell you from my own experience that ARM really has minimal interest in this area and has explored it far less than other CPU companies.

You don't really pay extra power for speculating. If you compare two well-designed systems; one can run the same software on 2 threads and one on 4 threads...there's going to be quite a performance gap. So as long as your speculative overhead isn't 50%, you're probably OK.

Mis-speculation can consume quite a bit of power, but that just means you have to be careful.

> To repeat, I don't believe there are any optimizations which are much better done in a JIT than in
> a static compiler. Even dynamic info like profiling works better when done the >traditional way.

You're welcome to believe that, but you'd be wrong. I've seen plenty of data to the contrary.

Moreover, there's plenty of public data from TMTA about optimizations which are only possible through JITing.

DK
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TopicPosted ByDate
New Article: ARM Goes 64-bitDavid Kanter2012/08/14 12:04 AM
  New Article: ARM Goes 64-bitnone2012/08/14 12:44 AM
    New Article: ARM Goes 64-bitDavid Kanter2012/08/14 01:04 AM
    MIPS MT-ASEPaul A. Clayton2012/08/14 09:01 AM
      MONITOR/MWAITEduardoS2012/08/14 10:08 AM
        MWAIT not specifically MTPaul A. Clayton2012/08/14 10:36 AM
          MWAIT not specifically MTEduardoS2012/08/15 03:16 PM
        MONITOR/MWAITanonymou52012/08/14 11:07 AM
          MONITOR/MWAITEduardoS2012/08/15 03:20 PM
      MIPS MT-ASErwessel2012/08/14 10:14 AM
  New Article: ARM Goes 64-bitSHK2012/08/14 02:01 AM
  New Article: ARM Goes 64-bitanon2012/08/14 02:37 AM
    New Article: ARM Goes 64-bitRichard Cownie2012/08/14 03:57 AM
      New Article: ARM Goes 64-bitanon2012/08/14 04:29 AM
      New Article: ARM Goes 64-bitnone2012/08/14 04:44 AM
        New Article: ARM Goes 64-bitanon2012/08/14 05:28 AM
          New Article: ARM Goes 64-bitanon2012/08/14 05:32 AM
            New Article: ARM Goes 64-bitEduardoS2012/08/14 06:06 AM
          New Article: ARM Goes 64-bitnone2012/08/14 05:40 AM
            AArch64 select better than cmovPaul A. Clayton2012/08/14 06:08 AM
            New Article: ARM Goes 64-bitanon2012/08/14 06:12 AM
              New Article: ARM Goes 64-bitnone2012/08/14 06:25 AM
                Predicated ld/store are usefulPaul A. Clayton2012/08/14 06:48 AM
                  Predicated ld/store are usefulnone2012/08/14 06:56 AM
                    Predicated ld/store are usefulanon2012/08/14 07:07 AM
                    Predicated stores might not be that badPaul A. Clayton2012/08/14 07:27 AM
                      Predicated stores might not be that badDavid Kanter2012/08/15 01:14 AM
                        Predicated stores might not be that badMichael S2012/08/15 11:41 AM
                        Predicated stores might not be that badR Byron2012/08/17 04:09 AM
                New Article: ARM Goes 64-bitanon2012/08/14 06:54 AM
                  New Article: ARM Goes 64-bitnone2012/08/14 07:04 AM
                    New Article: ARM Goes 64-bitanon2012/08/14 07:43 AM
          New Article: ARM Goes 64-bitEduardoS2012/08/14 06:07 AM
            New Article: ARM Goes 64-bitanon2012/08/14 06:20 AM
              New Article: ARM Goes 64-bitnone2012/08/14 06:29 AM
                New Article: ARM Goes 64-bitanon2012/08/14 07:00 AM
            New Article: ARM Goes 64-bitMichael S2012/08/14 03:43 PM
        New Article: ARM Goes 64-bitRichard Cownie2012/08/14 06:53 AM
          OT: Conrad's "Youth"Richard Cownie2012/08/14 07:20 AM
      New Article: ARM Goes 64-bitEduardoS2012/08/14 06:04 AM
        New Article: ARM Goes 64-bitmpx2012/08/14 08:59 AM
          New Article: ARM Goes 64-bitAntti-Ville Tuunainen2012/08/14 09:16 AM
        New Article: ARM Goes 64-bitanonymou52012/08/14 11:03 AM
          New Article: ARM Goes 64-bitname992012/11/17 03:31 PM
            Microarchitecting a counter registerPaul A. Clayton2012/11/17 07:37 PM
    New Article: ARM Goes 64-bitbakaneko2012/08/14 04:21 AM
      New Article: ARM Goes 64-bitname992012/11/17 03:40 PM
        New Article: ARM Goes 64-bitEduardoS2012/11/17 04:52 PM
        New Article: ARM Goes 64-bitDoug S2012/11/17 05:48 PM
        New Article: ARM Goes 64-bitbakaneko2012/11/18 05:40 PM
          New Article: ARM Goes 64-bitWilco2012/11/19 07:59 AM
            New Article: ARM Goes 64-bitEduardoS2012/11/19 08:23 AM
              New Article: ARM Goes 64-bitWilco2012/11/19 09:31 AM
                Downloading µarch-specific binaries?Paul A. Clayton2012/11/19 11:21 AM
                New Article: ARM Goes 64-bitEduardoS2012/11/19 11:41 AM
                  New Article: ARM Goes 64-bitWilco2012/11/21 07:44 AM
                    JIT vs. static compilation (Was: New Article: ARM Goes 64-bit)VMguy2012/11/22 03:21 AM
                      JIT vs. static compilation (Was: New Article: ARM Goes 64-bit)David Kanter2012/11/22 12:12 PM
                        JIT vs. static compilation (Was: New Article: ARM Goes 64-bit)Gabriele Svelto2012/11/23 03:50 AM
                    New Article: ARM Goes 64-bitEduardoS2012/11/23 10:09 AM
                      New Article: ARM Goes 64-bitEBFE2012/11/26 01:24 AM
                        New Article: ARM Goes 64-bitGabriele Svelto2012/11/26 03:33 AM
                          New Article: ARM Goes 64-bitEBFE2012/11/27 11:17 PM
                            New Article: ARM Goes 64-bitGabriele Svelto2012/11/28 02:32 AM
                        New Article: ARM Goes 64-bitEduardoS2012/11/26 12:16 PM
                          New Article: ARM Goes 64-bitEBFE2012/11/28 12:33 AM
                            New Article: ARM Goes 64-bitEduardoS2012/11/28 05:53 AM
                              New Article: ARM Goes 64-bitMichael S2012/11/28 06:15 AM
                                New Article: ARM Goes 64-bitEduardoS2012/11/28 07:33 AM
                                  New Article: ARM Goes 64-bitMichael S2012/11/28 09:16 AM
                                    New Article: ARM Goes 64-bitEduardoS2012/11/28 09:53 AM
                                    New Article: ARM Goes 64-bitEugene Nalimov2012/11/28 05:58 PM
                                      Amazing!EduardoS2012/11/28 07:25 PM
                                        Amazing! (non-italic response)EduardoS2012/11/28 07:25 PM
                                        Amazing!EBFE2012/11/28 08:20 PM
                                          Undefined behaviour doubles downEduardoS2012/11/28 09:10 PM
                              New Article: ARM Goes 64-bitEBFE2012/11/28 07:54 PM
                                New Article: ARM Goes 64-bitEduardoS2012/11/28 09:21 PM
                Have you heard of Transmeta?David Kanter2012/11/19 03:47 PM
            New Article: ARM Goes 64-bitbakaneko2012/11/19 09:08 AM
            New Article: ARM Goes 64-bitDavid Kanter2012/11/19 03:40 PM
              Semantic Dictionary EncodingRay2012/11/19 10:37 PM
              New Article: ARM Goes 64-bitRohit2012/11/20 04:48 PM
                New Article: ARM Goes 64-bitDavid Kanter2012/11/20 11:07 PM
                  New Article: ARM Goes 64-bitWilco2012/11/21 06:41 AM
                    New Article: ARM Goes 64-bitDavid Kanter2012/11/21 10:12 AM
                    A JIT exampleMark Roulo2012/11/21 10:30 AM
                      A JIT exampleWilco2012/11/21 07:04 PM
                        A JIT examplerwessel2012/11/21 09:05 PM
                        A JIT exampleGabriele Svelto2012/11/23 03:53 AM
                        A JIT exampleEduardoS2012/11/23 10:13 AM
                          A JIT exampleWilco2012/11/23 01:41 PM
                            A JIT exampleEduardoS2012/11/23 02:06 PM
                            A JIT exampleGabriele Svelto2012/11/23 04:09 PM
                              A JIT exampleSymmetry2012/11/26 05:58 AM
            New Article: ARM Goes 64-bitRay2012/11/19 10:27 PM
    New Article: ARM Goes 64-bitDavid Kanter2012/08/14 09:11 AM
  v7-M is Thumb-onlyPaul A. Clayton2012/08/14 06:58 AM
  Minor suggested correctionPaul A. Clayton2012/08/14 08:33 AM
    Minor suggested correctionanon2012/08/14 08:57 AM
  New Article: ARM Goes 64-bitExophase2012/08/14 08:33 AM
    New Article: ARM Goes 64-bitDavid Kanter2012/08/14 09:16 AM
      New Article: ARM Goes 64-bitjigal2012/08/15 01:49 PM
  Correction re ARM and BBC MicroPaul2012/08/14 08:59 PM
    Correction re ARM and BBC MicroPer Hesselgren2012/08/15 03:27 AM
  Memory BW so lowPer Hesselgren2012/08/15 03:14 AM
    Memory BW so lownone2012/08/15 11:16 AM
  New Article: ARM Goes 64-bitdado2012/08/15 10:25 AM
  Number of GPRsKenneth Jonsson2012/08/16 02:35 PM
    Number of GPRsExophase2012/08/16 02:52 PM
      Number of GPRsKenneth Jonsson2012/08/17 02:41 AM
        Ooops, missing link...Kenneth Jonsson2012/08/17 02:44 AM
        64-bit pointers eat some performancePaul A. Clayton2012/08/17 06:19 AM
          64-bit pointers eat some performancebakaneko2012/08/17 08:37 AM
            Brute force seems to workPaul A. Clayton2012/08/17 10:08 AM
              Brute force seems to workbakaneko2012/08/17 11:15 AM
          64-bit pointers eat some performanceRichard Cownie2012/08/17 08:46 AM
            Pointer compression is atypicalPaul A. Clayton2012/08/17 10:43 AM
              Pointer compression is atypicalRichard Cownie2012/08/17 12:57 PM
                Pointer compression is atypicalHoward Chu2012/08/22 10:17 PM
                  Pointer compression is atypicalRichard Cownie2012/08/23 04:48 AM
                    Pointer compression is atypicalHoward Chu2012/08/23 06:51 AM
              Pointer compression is atypicalWilco2012/08/17 02:41 PM
                Pointer compression is atypicalRichard Cownie2012/08/17 04:13 PM
                  Pointer compression is atypicalRicardo B2012/08/19 10:44 AM
                  Pointer compression is atypicalHoward Chu2012/08/22 10:08 PM
                    Unified libraries?Paul A. Clayton2012/08/23 07:49 AM
                    Pointer compression is atypicalRichard Cownie2012/08/23 08:44 AM
                      Pointer compression is atypicalHoward Chu2012/08/23 05:17 PM
                        Pointer compression is atypicalanon2012/08/23 08:15 PM
                          Pointer compression is atypicalHoward Chu2012/08/23 09:33 PM
            64-bit pointers eat some performanceFoo_2012/08/18 12:09 PM
              64-bit pointers eat some performanceRichard Cownie2012/08/18 05:25 PM
                64-bit pointers eat some performanceRichard Cownie2012/08/18 05:32 PM
            Page-related benefit of small pointersPaul A. Clayton2012/08/23 08:36 AM
        Number of GPRsWilco2012/08/17 06:31 AM
          Number of GPRsKenneth Jonsson2012/08/17 11:54 AM
            Number of GPRsExophase2012/08/17 12:44 PM
              Number of GPRsKenneth Jonsson2012/08/17 01:22 PM
                Number of GPRsWilco2012/08/17 02:53 PM
        What about dynamic utilization?Exophase2012/08/17 09:30 AM
          Compiler vs. assembly aliasing knowledge?Paul A. Clayton2012/08/17 10:20 AM
            Compiler vs. assembly aliasing knowledge?Exophase2012/08/17 11:09 AM
            Compiler vs. assembly aliasing knowledge?anon2012/08/18 02:23 AM
              Compiler vs. assembly aliasing knowledge?Ricardo B2012/08/19 11:02 AM
                Compiler vs. assembly aliasing knowledge?anon2012/08/19 06:07 PM
                  Compiler vs. assembly aliasing knowledge?Ricardo B2012/08/19 07:26 PM
                    Compiler vs. assembly aliasing knowledge?anon2012/08/19 10:03 PM
                      Compiler vs. assembly aliasing knowledge?anon2012/08/20 01:59 AM
        Number of GPRsDavid Kanter2012/08/17 12:46 PM
          RAT issues as part of reason 1Paul A. Clayton2012/08/17 02:18 PM
        Number of GPRsname992012/11/17 06:37 PM
          Large ARFs increase renaming costPaul A. Clayton2012/11/17 09:23 PM
    Number of GPRsDavid Kanter2012/08/16 03:31 PM
    Number of GPRsRichard Cownie2012/08/16 05:17 PM
    32 GPRs ~2-3%Paul A. Clayton2012/08/16 06:27 PM
      Oops, Message-ID: aaed6e38-c7bd-467e-ba41-f40cf1020e5e@googlegroups.com (NT)Paul A. Clayton2012/08/16 06:29 PM
      32 GPRs ~2-3%Exophase2012/08/16 10:06 PM
        R31 as SP/zero is kind of neat (NT)Paul A. Clayton2012/08/17 06:23 AM
        32 GPRs ~2-3%rwessel2012/08/17 08:24 AM
          32 GPRs ~2-3%Exophase2012/08/17 09:16 AM
            32 GPRs ~2-3%Max2012/08/17 04:19 PM
      32 GPRs ~2-3%name992012/11/17 07:43 PM
    Number of GPRsmpx2012/08/17 01:11 AM
      Latency and powerPaul A. Clayton2012/08/17 06:54 AM
    Number of GPRsbakaneko2012/08/17 03:09 AM
  New Article: ARM Goes 64-bitSteve2012/08/17 02:12 PM
    New Article: ARM Goes 64-bitDavid Kanter2012/08/19 12:42 PM
      New Article: ARM Goes 64-bitDoug S2012/08/19 02:02 PM
      New Article: ARM Goes 64-bitAnon2012/08/19 07:16 PM
      New Article: ARM Goes 64-bitSteve2012/08/30 07:51 AM
  Scalar vs Vector registersRobert David Graham2012/08/19 05:19 PM
    Scalar vs Vector registersDavid Kanter2012/08/19 05:29 PM
  New Article: ARM Goes 64-bitBaserock ARM servers2012/08/21 04:13 PM
    Baserock ARM serversSysanon2012/08/21 04:14 PM
    A-15 virtualization and LPAE?Paul A. Clayton2012/08/21 06:13 PM
      A-15 virtualization and LPAE?Anon2012/08/21 07:13 PM
        Half-depth advantages?Paul A. Clayton2012/08/21 08:42 PM
          Half-depth advantages?Anon2012/08/22 03:33 PM
            Thanks for the information (NT)Paul A. Clayton2012/08/22 04:04 PM
      A-15 virtualization and LPAE?C. Ladisch2012/08/23 11:12 AM
        A-15 virtualization and LPAE?Paul2012/08/23 03:17 PM
        Excessive pessimismPaul A. Clayton2012/08/23 04:08 PM
          Excessive pessimismDavid Kanter2012/08/23 05:05 PM
    New Article: ARM Goes 64-bitMichael S2012/08/22 07:12 AM
      BTW, Baserock==product, Codethink==company (NT)Paul A. Clayton2012/08/22 08:56 AM
  New Article: ARM Goes 64-bitReinoud Zandijk2012/08/21 11:27 PM
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