New Article: ARM Goes 64-bit

Article: ARM Goes 64-bit
By: EduardoS (no.delete@this.spam.com), November 26, 2012 12:16 pm
Room: Moderated Discussions
EBFE (x.delete@this.y.com) on November 26, 2012 1:24 am wrote:
> Background != Free
> App has to run slow interpreter/baseline compiler.
> Background compilation has a large working set and seriouly competes for LLC.

Background compilation means, when nothing else is using the processor, like, for example, during recharging, who cares about LLC when not using it?

> No, collecting short lived objects is expensive.

So, let's split short lived objects in two categories, those wich the compiler can prove can be allocated at the stack, where allocation and collection are free, but only a few VMs do this, and those wich are collected in the gen 0, and the collection cost is not being copyed to gen 1, once I heard from a VM programmer that they did not implement the logic to allocate objects in stack because gen 0 collections are so cheap that, in the end, there was no measurable performance difference.

> Copying is expensive.
> To make copying possible is also costy.

Copying is done on modern processors at a rate of 8 bytes per cycle or so, pointer derreference is done at a rate of one per 4 cycles, so copying is very cheap.

> However it does hurt throughput.

When there is a single thread of the app running use concurrent GC, when all processor threads are full use a non-concurrent GC, wich part of my previous statement is so hard to understand?

> Allocators waste space.
> VM allocators have no magic over C++ allocators, except that you can't customize.

VM allocators move objects arond to fill memory holes, C++ allocators can't.

> Such small cost accumalates and it results in visible penalty.

Ok, lists other small costs to see how much it accumulates

> Totally irrelevant.

Side note, sanity check as well, to avoid so many claims that C++ is fast by the spec because the spec treats almost everything as undefined behaviour, for our pleasure no compiler do the same.

> So you elaborated that VM has overhead because it has to take more care than C++.

You must take more care when reading.

> How can you know if there is a registered handler?

There is a try...catch block arround the code when there is a registered handler.

> C++ needs 0 check.

True, that's why almost every security flaw are in C/C++ program and almost every shipping C/C++ program is plagged by a security flaw at some point of it's live.

> The optimizer usually has to leave some check uneliminated unhoisted.
> And even redundant checks is diffcult to eliminate.

Yep, there are some proposals to make redundant checks easier to remove, but fortunally the optimizer is able to remove some of them.
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TopicPosted ByDate
New Article: ARM Goes 64-bitDavid Kanter08/14/12 12:04 AM
  New Article: ARM Goes 64-bitnone08/14/12 12:44 AM
    New Article: ARM Goes 64-bitDavid Kanter08/14/12 01:04 AM
    MIPS MT-ASEPaul A. Clayton08/14/12 09:01 AM
      MONITOR/MWAITEduardoS08/14/12 10:08 AM
        MWAIT not specifically MTPaul A. Clayton08/14/12 10:36 AM
          MWAIT not specifically MTEduardoS08/15/12 03:16 PM
        MONITOR/MWAITanonymou508/14/12 11:07 AM
          MONITOR/MWAITEduardoS08/15/12 03:20 PM
      MIPS MT-ASErwessel08/14/12 10:14 AM
  New Article: ARM Goes 64-bitSHK08/14/12 02:01 AM
  New Article: ARM Goes 64-bitanon08/14/12 02:37 AM
    New Article: ARM Goes 64-bitRichard Cownie08/14/12 03:57 AM
      New Article: ARM Goes 64-bitanon08/14/12 04:29 AM
      New Article: ARM Goes 64-bitnone08/14/12 04:44 AM
        New Article: ARM Goes 64-bitanon08/14/12 05:28 AM
          New Article: ARM Goes 64-bitanon08/14/12 05:32 AM
            New Article: ARM Goes 64-bitEduardoS08/14/12 06:06 AM
          New Article: ARM Goes 64-bitnone08/14/12 05:40 AM
            AArch64 select better than cmovPaul A. Clayton08/14/12 06:08 AM
            New Article: ARM Goes 64-bitanon08/14/12 06:12 AM
              New Article: ARM Goes 64-bitnone08/14/12 06:25 AM
                Predicated ld/store are usefulPaul A. Clayton08/14/12 06:48 AM
                  Predicated ld/store are usefulnone08/14/12 06:56 AM
                    Predicated ld/store are usefulanon08/14/12 07:07 AM
                    Predicated stores might not be that badPaul A. Clayton08/14/12 07:27 AM
                      Predicated stores might not be that badDavid Kanter08/15/12 01:14 AM
                        Predicated stores might not be that badMichael S08/15/12 11:41 AM
                        Predicated stores might not be that badR Byron08/17/12 04:09 AM
                New Article: ARM Goes 64-bitanon08/14/12 06:54 AM
                  New Article: ARM Goes 64-bitnone08/14/12 07:04 AM
                    New Article: ARM Goes 64-bitanon08/14/12 07:43 AM
          New Article: ARM Goes 64-bitEduardoS08/14/12 06:07 AM
            New Article: ARM Goes 64-bitanon08/14/12 06:20 AM
              New Article: ARM Goes 64-bitnone08/14/12 06:29 AM
                New Article: ARM Goes 64-bitanon08/14/12 07:00 AM
            New Article: ARM Goes 64-bitMichael S08/14/12 03:43 PM
        New Article: ARM Goes 64-bitRichard Cownie08/14/12 06:53 AM
          OT: Conrad's "Youth"Richard Cownie08/14/12 07:20 AM
      New Article: ARM Goes 64-bitEduardoS08/14/12 06:04 AM
        New Article: ARM Goes 64-bitmpx08/14/12 08:59 AM
          New Article: ARM Goes 64-bitAntti-Ville Tuunainen08/14/12 09:16 AM
        New Article: ARM Goes 64-bitanonymou508/14/12 11:03 AM
          New Article: ARM Goes 64-bitname9911/17/12 03:31 PM
            Microarchitecting a counter registerPaul A. Clayton11/17/12 07:37 PM
    New Article: ARM Goes 64-bitbakaneko08/14/12 04:21 AM
      New Article: ARM Goes 64-bitname9911/17/12 03:40 PM
        New Article: ARM Goes 64-bitEduardoS11/17/12 04:52 PM
        New Article: ARM Goes 64-bitDoug S11/17/12 05:48 PM
        New Article: ARM Goes 64-bitbakaneko11/18/12 05:40 PM
          New Article: ARM Goes 64-bitWilco11/19/12 07:59 AM
            New Article: ARM Goes 64-bitEduardoS11/19/12 08:23 AM
              New Article: ARM Goes 64-bitWilco11/19/12 09:31 AM
                Downloading µarch-specific binaries?Paul A. Clayton11/19/12 11:21 AM
                New Article: ARM Goes 64-bitEduardoS11/19/12 11:41 AM
                  New Article: ARM Goes 64-bitWilco11/21/12 07:44 AM
                    JIT vs. static compilation (Was: New Article: ARM Goes 64-bit)VMguy11/22/12 03:21 AM
                      JIT vs. static compilation (Was: New Article: ARM Goes 64-bit)David Kanter11/22/12 12:12 PM
                        JIT vs. static compilation (Was: New Article: ARM Goes 64-bit)Gabriele Svelto11/23/12 03:50 AM
                    New Article: ARM Goes 64-bitEduardoS11/23/12 10:09 AM
                      New Article: ARM Goes 64-bitEBFE11/26/12 01:24 AM
                        New Article: ARM Goes 64-bitGabriele Svelto11/26/12 03:33 AM
                          New Article: ARM Goes 64-bitEBFE11/27/12 11:17 PM
                            New Article: ARM Goes 64-bitGabriele Svelto11/28/12 02:32 AM
                        New Article: ARM Goes 64-bitEduardoS11/26/12 12:16 PM
                          New Article: ARM Goes 64-bitEBFE11/28/12 12:33 AM
                            New Article: ARM Goes 64-bitEduardoS11/28/12 05:53 AM
                              New Article: ARM Goes 64-bitMichael S11/28/12 06:15 AM
                                New Article: ARM Goes 64-bitEduardoS11/28/12 07:33 AM
                                  New Article: ARM Goes 64-bitMichael S11/28/12 09:16 AM
                                    New Article: ARM Goes 64-bitEduardoS11/28/12 09:53 AM
                                    New Article: ARM Goes 64-bitEugene Nalimov11/28/12 05:58 PM
                                      Amazing!EduardoS11/28/12 07:25 PM
                                        Amazing! (non-italic response)EduardoS11/28/12 07:25 PM
                                        Amazing!EBFE11/28/12 08:20 PM
                                          Undefined behaviour doubles downEduardoS11/28/12 09:10 PM
                              New Article: ARM Goes 64-bitEBFE11/28/12 07:54 PM
                                New Article: ARM Goes 64-bitEduardoS11/28/12 09:21 PM
                Have you heard of Transmeta?David Kanter11/19/12 03:47 PM
            New Article: ARM Goes 64-bitbakaneko11/19/12 09:08 AM
            New Article: ARM Goes 64-bitDavid Kanter11/19/12 03:40 PM
              Semantic Dictionary EncodingRay11/19/12 10:37 PM
              New Article: ARM Goes 64-bitRohit11/20/12 04:48 PM
                New Article: ARM Goes 64-bitDavid Kanter11/20/12 11:07 PM
                  New Article: ARM Goes 64-bitWilco11/21/12 06:41 AM
                    New Article: ARM Goes 64-bitDavid Kanter11/21/12 10:12 AM
                    A JIT exampleMark Roulo11/21/12 10:30 AM
                      A JIT exampleWilco11/21/12 07:04 PM
                        A JIT examplerwessel11/21/12 09:05 PM
                        A JIT exampleGabriele Svelto11/23/12 03:53 AM
                        A JIT exampleEduardoS11/23/12 10:13 AM
                          A JIT exampleWilco11/23/12 01:41 PM
                            A JIT exampleEduardoS11/23/12 02:06 PM
                            A JIT exampleGabriele Svelto11/23/12 04:09 PM
                              A JIT exampleSymmetry11/26/12 05:58 AM
            New Article: ARM Goes 64-bitRay11/19/12 10:27 PM
    New Article: ARM Goes 64-bitDavid Kanter08/14/12 09:11 AM
  v7-M is Thumb-onlyPaul A. Clayton08/14/12 06:58 AM
  Minor suggested correctionPaul A. Clayton08/14/12 08:33 AM
    Minor suggested correctionanon08/14/12 08:57 AM
  New Article: ARM Goes 64-bitExophase08/14/12 08:33 AM
    New Article: ARM Goes 64-bitDavid Kanter08/14/12 09:16 AM
      New Article: ARM Goes 64-bitjigal08/15/12 01:49 PM
  Correction re ARM and BBC MicroPaul08/14/12 08:59 PM
    Correction re ARM and BBC MicroPer Hesselgren08/15/12 03:27 AM
  Memory BW so lowPer Hesselgren08/15/12 03:14 AM
    Memory BW so lownone08/15/12 11:16 AM
  New Article: ARM Goes 64-bitdado08/15/12 10:25 AM
  Number of GPRsKenneth Jonsson08/16/12 02:35 PM
    Number of GPRsExophase08/16/12 02:52 PM
      Number of GPRsKenneth Jonsson08/17/12 02:41 AM
        Ooops, missing link...Kenneth Jonsson08/17/12 02:44 AM
        64-bit pointers eat some performancePaul A. Clayton08/17/12 06:19 AM
          64-bit pointers eat some performancebakaneko08/17/12 08:37 AM
            Brute force seems to workPaul A. Clayton08/17/12 10:08 AM
              Brute force seems to workbakaneko08/17/12 11:15 AM
          64-bit pointers eat some performanceRichard Cownie08/17/12 08:46 AM
            Pointer compression is atypicalPaul A. Clayton08/17/12 10:43 AM
              Pointer compression is atypicalRichard Cownie08/17/12 12:57 PM
                Pointer compression is atypicalHoward Chu08/22/12 10:17 PM
                  Pointer compression is atypicalRichard Cownie08/23/12 04:48 AM
                    Pointer compression is atypicalHoward Chu08/23/12 06:51 AM
              Pointer compression is atypicalWilco08/17/12 02:41 PM
                Pointer compression is atypicalRichard Cownie08/17/12 04:13 PM
                  Pointer compression is atypicalRicardo B08/19/12 10:44 AM
                  Pointer compression is atypicalHoward Chu08/22/12 10:08 PM
                    Unified libraries?Paul A. Clayton08/23/12 07:49 AM
                    Pointer compression is atypicalRichard Cownie08/23/12 08:44 AM
                      Pointer compression is atypicalHoward Chu08/23/12 05:17 PM
                        Pointer compression is atypicalanon08/23/12 08:15 PM
                          Pointer compression is atypicalHoward Chu08/23/12 09:33 PM
            64-bit pointers eat some performanceFoo_08/18/12 12:09 PM
              64-bit pointers eat some performanceRichard Cownie08/18/12 05:25 PM
                64-bit pointers eat some performanceRichard Cownie08/18/12 05:32 PM
            Page-related benefit of small pointersPaul A. Clayton08/23/12 08:36 AM
        Number of GPRsWilco08/17/12 06:31 AM
          Number of GPRsKenneth Jonsson08/17/12 11:54 AM
            Number of GPRsExophase08/17/12 12:44 PM
              Number of GPRsKenneth Jonsson08/17/12 01:22 PM
                Number of GPRsWilco08/17/12 02:53 PM
        What about dynamic utilization?Exophase08/17/12 09:30 AM
          Compiler vs. assembly aliasing knowledge?Paul A. Clayton08/17/12 10:20 AM
            Compiler vs. assembly aliasing knowledge?Exophase08/17/12 11:09 AM
            Compiler vs. assembly aliasing knowledge?anon08/18/12 02:23 AM
              Compiler vs. assembly aliasing knowledge?Ricardo B08/19/12 11:02 AM
                Compiler vs. assembly aliasing knowledge?anon08/19/12 06:07 PM
                  Compiler vs. assembly aliasing knowledge?Ricardo B08/19/12 07:26 PM
                    Compiler vs. assembly aliasing knowledge?anon08/19/12 10:03 PM
                      Compiler vs. assembly aliasing knowledge?anon08/20/12 01:59 AM
        Number of GPRsDavid Kanter08/17/12 12:46 PM
          RAT issues as part of reason 1Paul A. Clayton08/17/12 02:18 PM
        Number of GPRsname9911/17/12 06:37 PM
          Large ARFs increase renaming costPaul A. Clayton11/17/12 09:23 PM
    Number of GPRsDavid Kanter08/16/12 03:31 PM
    Number of GPRsRichard Cownie08/16/12 05:17 PM
    32 GPRs ~2-3%Paul A. Clayton08/16/12 06:27 PM
      Oops, Message-ID: aaed6e38-c7bd-467e-ba41-f40cf1020e5e@googlegroups.com (NT)Paul A. Clayton08/16/12 06:29 PM
      32 GPRs ~2-3%Exophase08/16/12 10:06 PM
        R31 as SP/zero is kind of neat (NT)Paul A. Clayton08/17/12 06:23 AM
        32 GPRs ~2-3%rwessel08/17/12 08:24 AM
          32 GPRs ~2-3%Exophase08/17/12 09:16 AM
            32 GPRs ~2-3%Max08/17/12 04:19 PM
      32 GPRs ~2-3%name9911/17/12 07:43 PM
    Number of GPRsmpx08/17/12 01:11 AM
      Latency and powerPaul A. Clayton08/17/12 06:54 AM
    Number of GPRsbakaneko08/17/12 03:09 AM
  New Article: ARM Goes 64-bitSteve08/17/12 02:12 PM
    New Article: ARM Goes 64-bitDavid Kanter08/19/12 12:42 PM
      New Article: ARM Goes 64-bitDoug S08/19/12 02:02 PM
      New Article: ARM Goes 64-bitAnon08/19/12 07:16 PM
      New Article: ARM Goes 64-bitSteve08/30/12 07:51 AM
  Scalar vs Vector registersRobert David Graham08/19/12 05:19 PM
    Scalar vs Vector registersDavid Kanter08/19/12 05:29 PM
  New Article: ARM Goes 64-bitBaserock ARM servers08/21/12 04:13 PM
    Baserock ARM serversSysanon08/21/12 04:14 PM
    A-15 virtualization and LPAE?Paul A. Clayton08/21/12 06:13 PM
      A-15 virtualization and LPAE?Anon08/21/12 07:13 PM
        Half-depth advantages?Paul A. Clayton08/21/12 08:42 PM
          Half-depth advantages?Anon08/22/12 03:33 PM
            Thanks for the information (NT)Paul A. Clayton08/22/12 04:04 PM
      A-15 virtualization and LPAE?C. Ladisch08/23/12 11:12 AM
        A-15 virtualization and LPAE?Paul08/23/12 03:17 PM
        Excessive pessimismPaul A. Clayton08/23/12 04:08 PM
          Excessive pessimismDavid Kanter08/23/12 05:05 PM
    New Article: ARM Goes 64-bitMichael S08/22/12 07:12 AM
      BTW, Baserock==product, Codethink==company (NT)Paul A. Clayton08/22/12 08:56 AM
  New Article: ARM Goes 64-bitReinoud Zandijk08/21/12 11:27 PM
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