A bit off base

Article: PhysX87: Software Deficiency
By: Ian Ameline (ian.ameline.delete@this.gmail.com), July 11, 2010 6:51 am
Room: Moderated Discussions
Michael S (already5chosen@yahoo.com) on 7/10/10 wrote:
>Ian Ameline (ian.ameline@gmail.com) on 7/9/10 wrote:
>>David Kanter (dkanter@realworldtech.com) on 7/8/10 wrote:
>>>That's simply not true. I've already made it clear that if we compare a high-end
>>>GPU to a high-end CPU, the GPU has at best a 8X advantage in FLOP/s and 5.5X in memory bandwidth. 5.5 < 8 < 10.
>>There are some other things the GPU can do better than the CPU. If you need fast
>>but not perfectly accurate sqrt or trig fcns, the GPU apparently can do those much
>>faster than the CPU. Similarly, the texture samplers can be very helpful -- if you
>>need to do 1d, 2d, or 3d table lookups with interpolation, the texture samplers
>>with their caches can be very fast. (Just remember that those caches are not coherent
>>with any other part of the caches on the GPU.)
>>So it is possible (but not easy) to get greater speedup on the GPU than the 5.5x
>>bandwidth or 8x flops would lead you to expect.
>>-- Ian.
>Very good point, IMHO, esp about utilizing texture units.
>However I don't quite understand what you are saying about approximation of sqrt.
>On Intel CPUs RSQRTPS has half the throughput of ADDPS and the same latency. On
>the new AMD processors it is faster yet - same throughput as ADDPS.
>Do GPUs have even better ratio between calculation of approximate sqrt and regular arithmetics?

No similar throughput and latency on GPUs, but rsqrtps produces 12 good bits of precision in the fraction. On GPUs, you can get much more (being deliberately vague, as I recall being told the exact precision by one GPU vendor a number of years ago, but I'm reasonably sure that my recollection also includes the fact that the whole meeting/conversation was covered by an NDA.)


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TopicPosted ByDate
A bit off baseJohn Mann2010/07/07 06:04 AM
  A bit off baseDavid Kanter2010/07/07 10:28 AM
    SSE vs x87Joel Hruska2010/07/07 11:53 AM
      SSE vs x87Michael S2010/07/07 12:07 PM
        SSE vs x87hobold2010/07/08 04:12 AM
      SSE vs x87David Kanter2010/07/07 01:55 PM
        SSE vs x87Andi Kleen2010/07/08 01:43 AM
          80 bit FPRicardo B2010/07/08 06:35 AM
            80 bit FPDavid Kanter2010/07/08 10:14 AM
              80 bit FPKevin G2010/07/08 01:12 PM
                80 bit FPIan Ollmann2010/07/18 11:49 PM
                  80 bit FPDavid Kanter2010/07/19 10:33 AM
                    80 bit FPAnil Maliyekkel2010/07/19 03:49 PM
                      80 bit FPrwessel2010/07/19 04:41 PM
                    80 bit FPMatt Waldhauer2010/07/21 10:11 AM
            80 bit FPEmil Briggs2010/07/22 08:06 AM
    A bit off baseJohn Mann2010/07/08 10:06 AM
      A bit off baseDavid Kanter2010/07/08 10:27 AM
        A bit off baseIan Ameline2010/07/09 09:10 AM
          A bit off baseMichael S2010/07/10 01:13 PM
            A bit off baseIan Ameline2010/07/11 06:51 AM
  A bit off baseDavid Kanter2010/07/07 08:46 PM
    A bit off baseAnon2010/07/07 11:47 PM
      A bit off baseanon2010/07/08 01:15 AM
        A bit off baseGabriele Svelto2010/07/08 03:11 AM
          Physics engine historyPeter Clare2010/07/08 03:49 AM
            Physics engine historyNull Pointer Exception2010/07/08 05:07 AM
              Physics engine historyRalf2010/07/08 02:09 PM
                Physics engine historyDavid Kanter2010/07/08 03:16 PM
                  Physics engine historysJ2010/07/08 10:36 PM
                    Physics engine historyGabriele Svelto2010/07/08 11:59 PM
                      Physics engine historysJ2010/07/13 05:35 AM
                    Physics engine historyDavid Kanter2010/07/09 08:25 AM
                      Physics engine historysJ2010/07/13 05:49 AM
                      Physics engine historyfvdbergh2010/07/13 06:27 AM
    A bit off baseJohn Mann2010/07/08 10:11 AM
      A bit off baseDavid Kanter2010/07/08 10:31 AM
        150 GFLOP/s measured?anon2010/07/08 06:10 PM
          150 GFLOP/s measured?David Kanter2010/07/08 06:53 PM
            150 GFLOP/s measured?Aaron Spink2010/07/08 08:05 PM
              150 GFLOP/s measured?anon2010/07/08 08:31 PM
                150 GFLOP/s measured?Aaron Spink2010/07/08 09:43 PM
                  150 GFLOP/s measured?David Kanter2010/07/08 10:27 PM
                    150 GFLOP/s measured?Ian Ollmann2010/07/19 12:14 AM
                      150 GFLOP/s measured?anon2010/07/19 05:39 AM
                        150 GFLOP/s measured?hobold2010/07/19 06:26 AM
                          Philosophy for achieving peakDavid Kanter2010/07/19 10:49 AM
                      150 GFLOP/s measured?Linus Torvalds2010/07/19 06:36 AM
                        150 GFLOP/s measured?Richard Cownie2010/07/19 07:42 AM
                          150 GFLOP/s measured?Aaron Spink2010/07/19 07:56 AM
                            150 GFLOP/s measured?hobold2010/07/19 08:30 AM
                              150 GFLOP/s measured?Groo2010/07/19 01:31 PM
                                150 GFLOP/s measured?hobold2010/07/19 03:17 PM
                                  150 GFLOP/s measured?Groo2010/07/19 05:18 PM
                              150 GFLOP/s measured?Anon2010/07/19 05:18 PM
                            150 GFLOP/s measured?Mark Roulo2010/07/19 10:47 AM
                              150 GFLOP/s measured?slacker2010/07/19 11:55 AM
                                150 GFLOP/s measured?Mark Roulo2010/07/19 12:00 PM
                              150 GFLOP/s measured?anonymous422010/07/25 11:31 AM
                            150 GFLOP/s measured?Richard Cownie2010/07/19 11:41 AM
                              150 GFLOP/s measured?Linus Torvalds2010/07/19 01:57 PM
                                150 GFLOP/s measured?Richard Cownie2010/07/19 03:10 PM
                                150 GFLOP/s measured?Richard Cownie2010/07/19 03:10 PM
                                  150 GFLOP/s measured?hobold2010/07/19 03:25 PM
                                  150 GFLOP/s measured?Linus Torvalds2010/07/19 03:31 PM
                                    150 GFLOP/s measured?Richard Cownie2010/07/20 05:04 AM
                                150 GFLOP/s measured?jrl2010/07/20 12:18 AM
                            150 GFLOP/s measured?anonymous422010/07/25 11:00 AM
                              150 GFLOP/s measured?David Kanter2010/07/25 11:52 AM
                          150 GFLOP/s measured?Anon2010/07/19 05:15 PM
                            150 GFLOP/s measured?Linus Torvalds2010/07/19 06:27 PM
                              150 GFLOP/s measured?Anon2010/07/19 08:54 PM
                                150 GFLOP/s measured?anon2010/07/19 10:45 PM
                        150 GFLOP/s measured?hobold2010/07/19 08:14 AM
                          150 GFLOP/s measured?Linus Torvalds2010/07/19 10:56 AM
                            150 GFLOP/s measured?a reader2010/07/21 07:16 PM
                              150 GFLOP/s measured?Linus Torvalds2010/07/21 08:05 PM
                                150 GFLOP/s measured?anon2010/07/22 01:09 AM
                                  150 GFLOP/s measured?a reader2010/07/22 06:53 PM
                                    150 GFLOP/s measured?gallier22010/07/23 04:58 AM
                                      150 GFLOP/s measured?a reader2010/07/25 07:35 AM
                                        150 GFLOP/s measured?David Kanter2010/07/25 10:49 AM
                                          150 GFLOP/s measured?a reader2010/07/26 06:03 PM
                                            150 GFLOP/s measured?Michael S2010/07/28 12:38 AM
                                              150 GFLOP/s measured?Gabriele Svelto2010/07/28 12:44 AM
                                    150 GFLOP/s measured?anon2010/07/23 03:55 PM
                                      150 GFLOP/s measured?slacker2010/07/23 11:48 PM
                                        150 GFLOP/s measured?anon2010/07/24 01:36 AM
                                    150 GFLOP/s measured?Vincent Diepeveen2010/07/27 04:37 PM
                                      150 GFLOP/s measured??2010/07/27 10:42 PM
                                        150 GFLOP/s measured?slacker2010/07/28 04:55 AM
                                      Intel's clock rate projectionsAM2010/07/28 01:03 AM
                                        nostalgia ain't what it used to besomeone2010/07/28 04:38 AM
                                          Intel's clock rate projectionsAM2010/07/28 09:12 PM
                        Separate the OoO-ness from speculative-ness?2010/07/20 06:19 AM
                          Separate the OoO-ness from speculative-nessMark Christiansen2010/07/20 01:26 PM
                          Separate the OoO-ness from speculative-nessslacker2010/07/20 05:04 PM
                            Separate the OoO-ness from speculative-nessMatt Sayler2010/07/20 05:10 PM
                              Separate the OoO-ness from speculative-nessslacker2010/07/20 08:37 PM
                                Separate the OoO-ness from speculative-ness?2010/07/20 10:51 PM
                                  Separate the OoO-ness from speculative-nessanon2010/07/21 01:16 AM
                                    Separate the OoO-ness from speculative-ness?2010/07/21 06:05 AM
                                      Software conventionsPaul A. Clayton2010/07/21 07:52 AM
                                        Software conventions?2010/07/22 04:43 AM
                                      SpeculationDavid Kanter2010/07/21 09:32 AM
                                        Pipelining affects the ISA?2010/07/22 09:58 PM
                                          Pipelining affects the ISA?2010/07/22 10:14 PM
                                          Pipelining affects the ISArwessel2010/07/22 11:03 PM
                                            Pipelining affects the ISA?2010/07/23 04:50 AM
                                            Pipelining affects the ISA?2010/07/23 05:10 AM
                                              Pipelining affects the ISAThiago Kurovski2010/07/23 01:59 PM
                                                Pipelining affects the ISAanon2010/07/24 06:35 AM
                                                  Pipelining affects the ISAThiago Kurovski2010/07/24 10:12 AM
                                          Pipelining affects the ISAGabriele Svelto2010/07/26 01:50 AM
                                            Pipelining affects the ISAIlleglWpns2010/07/26 04:14 AM
                                              Pipelining affects the ISAMichael S2010/07/26 02:33 PM
                                      Separate the OoO-ness from speculative-nessanon2010/07/21 04:53 PM
                                        Separate the OoO-ness from speculative-ness?2010/07/22 03:15 AM
                                          Separate the OoO-ness from speculative-nessanon2010/07/22 03:27 AM
                                      Separate the OoO-ness from speculative-nessslacker2010/07/21 06:45 PM
                                        Separate the OoO-ness from speculative-nessanon2010/07/22 12:57 AM
                                        Separate the OoO-ness from speculative-ness?2010/07/22 04:26 AM
                                          Separate the OoO-ness from speculative-nessDan Downs2010/07/22 07:14 AM
                                          Confusing and not very useful definitionDavid Kanter2010/07/22 11:41 AM
                                            Confusing and not very useful definition?2010/07/22 09:58 PM
                                              Confusing and not very useful definitionUngo2010/07/24 11:06 AM
                                                Confusing and not very useful definition?2010/07/25 09:23 PM
                            Separate the OoO-ness from speculative-nesssomeone2010/07/20 07:02 PM
                              Separate the OoO-ness from speculative-nessThiago Kurovski2010/07/21 03:13 PM
            You are just quoting SINGLE precision flops? OMG what planet do you live? Vincent Diepeveen2010/07/19 09:26 AM
              The prior poster was talking about SP (NT)David Kanter2010/07/19 10:34 AM
                All FFT's need double precisionVincent Diepeveen2010/07/19 01:02 PM
                  All FFT's need double precisionDavid Kanter2010/07/19 01:09 PM
                    All FFT's need double precisionVincent Diepeveen2010/07/19 03:06 PM
                  All FFT's need double precision - notMichael S2010/07/20 12:16 AM
                    All FFT's need double precision - notUngo2010/07/20 11:04 PM
                      All FFT's need double precision - notMichael S2010/07/21 01:35 PM
                      All FFT's need double precision - notEduardoS2010/07/21 01:52 PM
                        All FFT's need double precision - notAnon2010/07/21 04:23 PM
                          All FFT's need double precision - notRicardo B2010/07/26 06:46 AM
                        I'm on a boat!anon2010/07/22 10:42 AM
                        All FFT's need double precision - notVincent Diepeveen2010/07/24 10:39 PM
                          All FFT's need double precision - notslacker2010/07/25 02:27 AM
                            All FFT's need double precision - notRicardo B2010/07/26 06:40 AM
                          All FFT's need double precision - notEduardoS2010/07/25 07:37 AM
                            All FFT's need double precision - notMichael S2010/07/25 09:43 AM
                    All FFT's need double precision - notVincent Diepeveen2010/07/24 10:19 PM
      A bit off baseEduardoS2010/07/08 03:08 PM
        A bit off baseGroo2010/07/08 05:11 PM
          A bit off basejohn mann2010/07/08 05:58 PM
            All right...let's cool it...David Kanter2010/07/08 06:54 PM
    A bit off baseVincent Diepeveen2010/07/19 02:36 PM
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