32 GPRs ~2-3%

Article: ARM Goes 64-bit
By: name99 (name99.delete@this.redheron.com), November 17, 2012 6:43 pm
Room: Moderated Discussions
Paul A. Clayton (paaronclayton.delete@this.gmail.com) on August 16, 2012 6:27 pm wrote:
> Kenneth Jonsson (kj.delete@this.localhost.org) on August 16, 2012 2:35 pm wrote:
> [snip]
> > More register does increase the cost of switching context, so unused
> > register cannot be a good thing.
> >
> > So what are the benefits of moving to 32
> > GPRs on ARMv8 from the current number of 16 (well 14 if one exclude PC and LR)?
>
(I vaguely recall some paper from IBM indicating that some FP workloads
> had loops with some register spilling due to register pressure even at 32 registers. If one uses the
> same fields for FP/SIMD and GPR register names, having a 5-bit field could be appropriate.)
>

Oh, FP is a COMPLETELY different issue, and the win for 32 registers is even higher.
To take two common kernels:

On something like x86, you really have to code an FFT as radix-2; on a PPC there are enough registers that you can code it as radix-8 without spilling. So one third the load/stores, a little less overhead; a lot less waiting around for ops to complete: maybe 50% to 100% faster than a radix-2 implementation, depending on how OoO your CPU is.

Secondly matrix multiplication. Of course any decent matrix multiplication coding is blocking at multiple levels, taking note of everything from TLB coverage to L2 to L1; but at the lowest level you will block to the number of registers, and once again more is better.
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New Article: ARM Goes 64-bitDavid Kanter2012/08/13 11:04 PM
  New Article: ARM Goes 64-bitnone2012/08/13 11:44 PM
    New Article: ARM Goes 64-bitDavid Kanter2012/08/14 12:04 AM
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      MONITOR/MWAITEduardoS2012/08/14 09:08 AM
        MWAIT not specifically MTPaul A. Clayton2012/08/14 09:36 AM
          MWAIT not specifically MTEduardoS2012/08/15 02:16 PM
        MONITOR/MWAITanonymou52012/08/14 10:07 AM
          MONITOR/MWAITEduardoS2012/08/15 02:20 PM
      MIPS MT-ASErwessel2012/08/14 09:14 AM
  New Article: ARM Goes 64-bitSHK2012/08/14 01:01 AM
  New Article: ARM Goes 64-bitanon2012/08/14 01:37 AM
    New Article: ARM Goes 64-bitRichard Cownie2012/08/14 02:57 AM
      New Article: ARM Goes 64-bitanon2012/08/14 03:29 AM
      New Article: ARM Goes 64-bitnone2012/08/14 03:44 AM
        New Article: ARM Goes 64-bitanon2012/08/14 04:28 AM
          New Article: ARM Goes 64-bitanon2012/08/14 04:32 AM
            New Article: ARM Goes 64-bitEduardoS2012/08/14 05:06 AM
          New Article: ARM Goes 64-bitnone2012/08/14 04:40 AM
            AArch64 select better than cmovPaul A. Clayton2012/08/14 05:08 AM
            New Article: ARM Goes 64-bitanon2012/08/14 05:12 AM
              New Article: ARM Goes 64-bitnone2012/08/14 05:25 AM
                Predicated ld/store are usefulPaul A. Clayton2012/08/14 05:48 AM
                  Predicated ld/store are usefulnone2012/08/14 05:56 AM
                    Predicated ld/store are usefulanon2012/08/14 06:07 AM
                    Predicated stores might not be that badPaul A. Clayton2012/08/14 06:27 AM
                      Predicated stores might not be that badDavid Kanter2012/08/15 12:14 AM
                        Predicated stores might not be that badMichael S2012/08/15 10:41 AM
                        Predicated stores might not be that badR Byron2012/08/17 03:09 AM
                New Article: ARM Goes 64-bitanon2012/08/14 05:54 AM
                  New Article: ARM Goes 64-bitnone2012/08/14 06:04 AM
                    New Article: ARM Goes 64-bitanon2012/08/14 06:43 AM
          New Article: ARM Goes 64-bitEduardoS2012/08/14 05:07 AM
            New Article: ARM Goes 64-bitanon2012/08/14 05:20 AM
              New Article: ARM Goes 64-bitnone2012/08/14 05:29 AM
                New Article: ARM Goes 64-bitanon2012/08/14 06:00 AM
            New Article: ARM Goes 64-bitMichael S2012/08/14 02:43 PM
        New Article: ARM Goes 64-bitRichard Cownie2012/08/14 05:53 AM
          OT: Conrad's "Youth"Richard Cownie2012/08/14 06:20 AM
      New Article: ARM Goes 64-bitEduardoS2012/08/14 05:04 AM
        New Article: ARM Goes 64-bitmpx2012/08/14 07:59 AM
          New Article: ARM Goes 64-bitAntti-Ville Tuunainen2012/08/14 08:16 AM
        New Article: ARM Goes 64-bitanonymou52012/08/14 10:03 AM
          New Article: ARM Goes 64-bitname992012/11/17 02:31 PM
            Microarchitecting a counter registerPaul A. Clayton2012/11/17 06:37 PM
    New Article: ARM Goes 64-bitbakaneko2012/08/14 03:21 AM
      New Article: ARM Goes 64-bitname992012/11/17 02:40 PM
        New Article: ARM Goes 64-bitEduardoS2012/11/17 03:52 PM
        New Article: ARM Goes 64-bitDoug S2012/11/17 04:48 PM
        New Article: ARM Goes 64-bitbakaneko2012/11/18 04:40 PM
          New Article: ARM Goes 64-bitWilco2012/11/19 06:59 AM
            New Article: ARM Goes 64-bitEduardoS2012/11/19 07:23 AM
              New Article: ARM Goes 64-bitWilco2012/11/19 08:31 AM
                Downloading µarch-specific binaries?Paul A. Clayton2012/11/19 10:21 AM
                New Article: ARM Goes 64-bitEduardoS2012/11/19 10:41 AM
                  New Article: ARM Goes 64-bitWilco2012/11/21 06:44 AM
                    JIT vs. static compilation (Was: New Article: ARM Goes 64-bit)VMguy2012/11/22 02:21 AM
                      JIT vs. static compilation (Was: New Article: ARM Goes 64-bit)David Kanter2012/11/22 11:12 AM
                        JIT vs. static compilation (Was: New Article: ARM Goes 64-bit)Gabriele Svelto2012/11/23 02:50 AM
                    New Article: ARM Goes 64-bitEduardoS2012/11/23 09:09 AM
                      New Article: ARM Goes 64-bitEBFE2012/11/26 12:24 AM
                        New Article: ARM Goes 64-bitGabriele Svelto2012/11/26 02:33 AM
                          New Article: ARM Goes 64-bitEBFE2012/11/27 10:17 PM
                            New Article: ARM Goes 64-bitGabriele Svelto2012/11/28 01:32 AM
                        New Article: ARM Goes 64-bitEduardoS2012/11/26 11:16 AM
                          New Article: ARM Goes 64-bitEBFE2012/11/27 11:33 PM
                            New Article: ARM Goes 64-bitEduardoS2012/11/28 04:53 AM
                              New Article: ARM Goes 64-bitMichael S2012/11/28 05:15 AM
                                New Article: ARM Goes 64-bitEduardoS2012/11/28 06:33 AM
                                  New Article: ARM Goes 64-bitMichael S2012/11/28 08:16 AM
                                    New Article: ARM Goes 64-bitEduardoS2012/11/28 08:53 AM
                                    New Article: ARM Goes 64-bitEugene Nalimov2012/11/28 04:58 PM
                                      Amazing!EduardoS2012/11/28 06:25 PM
                                        Amazing! (non-italic response)EduardoS2012/11/28 06:25 PM
                                        Amazing!EBFE2012/11/28 07:20 PM
                                          Undefined behaviour doubles downEduardoS2012/11/28 08:10 PM
                              New Article: ARM Goes 64-bitEBFE2012/11/28 06:54 PM
                                New Article: ARM Goes 64-bitEduardoS2012/11/28 08:21 PM
                Have you heard of Transmeta?David Kanter2012/11/19 02:47 PM
            New Article: ARM Goes 64-bitbakaneko2012/11/19 08:08 AM
            New Article: ARM Goes 64-bitDavid Kanter2012/11/19 02:40 PM
              Semantic Dictionary EncodingRay2012/11/19 09:37 PM
              New Article: ARM Goes 64-bitRohit2012/11/20 03:48 PM
                New Article: ARM Goes 64-bitDavid Kanter2012/11/20 10:07 PM
                  New Article: ARM Goes 64-bitWilco2012/11/21 05:41 AM
                    New Article: ARM Goes 64-bitDavid Kanter2012/11/21 09:12 AM
                    A JIT exampleMark Roulo2012/11/21 09:30 AM
                      A JIT exampleWilco2012/11/21 06:04 PM
                        A JIT examplerwessel2012/11/21 08:05 PM
                        A JIT exampleGabriele Svelto2012/11/23 02:53 AM
                        A JIT exampleEduardoS2012/11/23 09:13 AM
                          A JIT exampleWilco2012/11/23 12:41 PM
                            A JIT exampleEduardoS2012/11/23 01:06 PM
                            A JIT exampleGabriele Svelto2012/11/23 03:09 PM
                              A JIT exampleSymmetry2012/11/26 04:58 AM
            New Article: ARM Goes 64-bitRay2012/11/19 09:27 PM
    New Article: ARM Goes 64-bitDavid Kanter2012/08/14 08:11 AM
  v7-M is Thumb-onlyPaul A. Clayton2012/08/14 05:58 AM
  Minor suggested correctionPaul A. Clayton2012/08/14 07:33 AM
    Minor suggested correctionanon2012/08/14 07:57 AM
  New Article: ARM Goes 64-bitExophase2012/08/14 07:33 AM
    New Article: ARM Goes 64-bitDavid Kanter2012/08/14 08:16 AM
      New Article: ARM Goes 64-bitjigal2012/08/15 12:49 PM
  Correction re ARM and BBC MicroPaul2012/08/14 07:59 PM
    Correction re ARM and BBC MicroPer Hesselgren2012/08/15 02:27 AM
  Memory BW so lowPer Hesselgren2012/08/15 02:14 AM
    Memory BW so lownone2012/08/15 10:16 AM
  New Article: ARM Goes 64-bitdado2012/08/15 09:25 AM
  Number of GPRsKenneth Jonsson2012/08/16 01:35 PM
    Number of GPRsExophase2012/08/16 01:52 PM
      Number of GPRsKenneth Jonsson2012/08/17 01:41 AM
        Ooops, missing link...Kenneth Jonsson2012/08/17 01:44 AM
        64-bit pointers eat some performancePaul A. Clayton2012/08/17 05:19 AM
          64-bit pointers eat some performancebakaneko2012/08/17 07:37 AM
            Brute force seems to workPaul A. Clayton2012/08/17 09:08 AM
              Brute force seems to workbakaneko2012/08/17 10:15 AM
          64-bit pointers eat some performanceRichard Cownie2012/08/17 07:46 AM
            Pointer compression is atypicalPaul A. Clayton2012/08/17 09:43 AM
              Pointer compression is atypicalRichard Cownie2012/08/17 11:57 AM
                Pointer compression is atypicalHoward Chu2012/08/22 09:17 PM
                  Pointer compression is atypicalRichard Cownie2012/08/23 03:48 AM
                    Pointer compression is atypicalHoward Chu2012/08/23 05:51 AM
              Pointer compression is atypicalWilco2012/08/17 01:41 PM
                Pointer compression is atypicalRichard Cownie2012/08/17 03:13 PM
                  Pointer compression is atypicalRicardo B2012/08/19 09:44 AM
                  Pointer compression is atypicalHoward Chu2012/08/22 09:08 PM
                    Unified libraries?Paul A. Clayton2012/08/23 06:49 AM
                    Pointer compression is atypicalRichard Cownie2012/08/23 07:44 AM
                      Pointer compression is atypicalHoward Chu2012/08/23 04:17 PM
                        Pointer compression is atypicalanon2012/08/23 07:15 PM
                          Pointer compression is atypicalHoward Chu2012/08/23 08:33 PM
            64-bit pointers eat some performanceFoo_2012/08/18 11:09 AM
              64-bit pointers eat some performanceRichard Cownie2012/08/18 04:25 PM
                64-bit pointers eat some performanceRichard Cownie2012/08/18 04:32 PM
            Page-related benefit of small pointersPaul A. Clayton2012/08/23 07:36 AM
        Number of GPRsWilco2012/08/17 05:31 AM
          Number of GPRsKenneth Jonsson2012/08/17 10:54 AM
            Number of GPRsExophase2012/08/17 11:44 AM
              Number of GPRsKenneth Jonsson2012/08/17 12:22 PM
                Number of GPRsWilco2012/08/17 01:53 PM
        What about dynamic utilization?Exophase2012/08/17 08:30 AM
          Compiler vs. assembly aliasing knowledge?Paul A. Clayton2012/08/17 09:20 AM
            Compiler vs. assembly aliasing knowledge?Exophase2012/08/17 10:09 AM
            Compiler vs. assembly aliasing knowledge?anon2012/08/18 01:23 AM
              Compiler vs. assembly aliasing knowledge?Ricardo B2012/08/19 10:02 AM
                Compiler vs. assembly aliasing knowledge?anon2012/08/19 05:07 PM
                  Compiler vs. assembly aliasing knowledge?Ricardo B2012/08/19 06:26 PM
                    Compiler vs. assembly aliasing knowledge?anon2012/08/19 09:03 PM
                      Compiler vs. assembly aliasing knowledge?anon2012/08/20 12:59 AM
        Number of GPRsDavid Kanter2012/08/17 11:46 AM
          RAT issues as part of reason 1Paul A. Clayton2012/08/17 01:18 PM
        Number of GPRsname992012/11/17 05:37 PM
          Large ARFs increase renaming costPaul A. Clayton2012/11/17 08:23 PM
    Number of GPRsDavid Kanter2012/08/16 02:31 PM
    Number of GPRsRichard Cownie2012/08/16 04:17 PM
    32 GPRs ~2-3%Paul A. Clayton2012/08/16 05:27 PM
      Oops, Message-ID: aaed6e38-c7bd-467e-ba41-f40cf1020e5e@googlegroups.com (NT)Paul A. Clayton2012/08/16 05:29 PM
      32 GPRs ~2-3%Exophase2012/08/16 09:06 PM
        R31 as SP/zero is kind of neat (NT)Paul A. Clayton2012/08/17 05:23 AM
        32 GPRs ~2-3%rwessel2012/08/17 07:24 AM
          32 GPRs ~2-3%Exophase2012/08/17 08:16 AM
            32 GPRs ~2-3%Max2012/08/17 03:19 PM
      32 GPRs ~2-3%name992012/11/17 06:43 PM
    Number of GPRsmpx2012/08/17 12:11 AM
      Latency and powerPaul A. Clayton2012/08/17 05:54 AM
    Number of GPRsbakaneko2012/08/17 02:09 AM
  New Article: ARM Goes 64-bitSteve2012/08/17 01:12 PM
    New Article: ARM Goes 64-bitDavid Kanter2012/08/19 11:42 AM
      New Article: ARM Goes 64-bitDoug S2012/08/19 01:02 PM
      New Article: ARM Goes 64-bitAnon2012/08/19 06:16 PM
      New Article: ARM Goes 64-bitSteve2012/08/30 06:51 AM
  Scalar vs Vector registersRobert David Graham2012/08/19 04:19 PM
    Scalar vs Vector registersDavid Kanter2012/08/19 04:29 PM
  New Article: ARM Goes 64-bitBaserock ARM servers2012/08/21 03:13 PM
    Baserock ARM serversSysanon2012/08/21 03:14 PM
    A-15 virtualization and LPAE?Paul A. Clayton2012/08/21 05:13 PM
      A-15 virtualization and LPAE?Anon2012/08/21 06:13 PM
        Half-depth advantages?Paul A. Clayton2012/08/21 07:42 PM
          Half-depth advantages?Anon2012/08/22 02:33 PM
            Thanks for the information (NT)Paul A. Clayton2012/08/22 03:04 PM
      A-15 virtualization and LPAE?C. Ladisch2012/08/23 10:12 AM
        A-15 virtualization and LPAE?Paul2012/08/23 02:17 PM
        Excessive pessimismPaul A. Clayton2012/08/23 03:08 PM
          Excessive pessimismDavid Kanter2012/08/23 04:05 PM
    New Article: ARM Goes 64-bitMichael S2012/08/22 06:12 AM
      BTW, Baserock==product, Codethink==company (NT)Paul A. Clayton2012/08/22 07:56 AM
  New Article: ARM Goes 64-bitReinoud Zandijk2012/08/21 10:27 PM
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