New Article: ARM Goes 64-bit

Article: ARM Goes 64-bit
By: Wilco (Wilco.Dijkstra.delete@this.ntlworld.com), November 19, 2012 9:31 am
Room: Moderated Discussions
EduardoS (no.delete@this.spam.com) on November 19, 2012 8:23 am wrote:
> Wilco (Wilco.Dijkstra.delete@this.ntlworld.com) on November 19, 2012 7:59 am wrote:
> > As a compiler expert I'm sceptical that virtual machines can ever deliver close to native performance. The
> > key issue with JIT compilation is that you just do not have the resources of a native compiler. It doesn't
> > help that many intermediate bytecodes are completely unoptimized, making the problem far worse (what is the
> > point of Java compilers emitting x * 0 in byte codes?!?).
> > What you actually want to do is to perform as much
> > work as possible in the static compiler and end up with
> > a highly optimized intermediate code that just needs
> > to be converted into the final target assembly with a quick
> > peephole pass. For example you want to do register
> > allocation to a virtual 16-register target (so it maps trivially to Thumb-2, ARM64 and x64).
>
> Yep, JITs will hardly outperform time consuming compilers, but what prevents a virtual machine
> from using a background compiling service to store native images like .Net ngen does?

That certainly helps, but you're still doing it multiple times on targets which may not have a lot of resources. What is more efficient - every phone compiling every bit of software you download, or just run a highly optimized binary which was compiled once with optimal settings on fast hardware?

So with JIT compilation you get the double whammy of having to waste energy on compilation as well as waste energy due to this compilation not being optimal.

> > The other issue is C++ vs managed languages. GC, exceptions and other features have a lot of overhead
> > (even when unused), so you're never going to be anywhere near as fast as a well written C++ program.
>
> First, C++ also have exceptions, they does not reduce performance but
> also remove the exception handling code from the critical path.

Exceptions most definitely reduce performance, even for code that doesn't use it. And that is true for C++ too, but to a lesser extent. At ARM we put a lot of effort into compiling C++ with exceptions almost as efficiently as without, so it is possible to get close. But in some languages it gets really difficult as just about any operation can cause an exception, blocking most optimizations.

> Second, today, in the real world, where cache locality becomes more important than micro-optimizations
> GC actually improves performance in some cases over simple memory management, sure, one can
> implement a more complex memory management in C++, one can even implement GC in C++, it can
> be done in assembly as well, but it is so complex that nobody does.

Cache locality is certainly important, but GC doesn't solve that - in reality it actually makes it worse. And that is before we consider the actual overhead of the collection itself, often having to stop all threads for long periods. Then there is the optimization overhead and extra tables causing code bloat.

> So only left is the overhead of other features wich you didn't even listed.

For example arithmetic with overflow, array bounds checks, null pointer checks, assuming any pointer access may cause an exception, multithreading support etc etc.

> And you completly forgot to mention the uncomparable effort already spent to make C++ compilers.

It's not like languages like Java or C# are new. It is significantly harder to write a good compiler for them, and even then you can never get close to C++ performance. Many optimizations have to be disabled or turned extremely conservative as an exception or GC may occur at any time.

Obviously you could argue all the overhead is worth it as some of the features allow programmers to write code faster. Whether that is a good or a bad thing is a different discussion altogether...

Wilco
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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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