A bit off base

Article: PhysX87: Software Deficiency
By: David Kanter (dkanter.delete@this.realworldtech.com), July 8, 2010 11:27 am
Room: Moderated Discussions
John Mann (xman52373@aol.com) on 7/8/10 wrote:
---------------------------
>David Kanter (dkanter@realworldtech.com) on 7/7/10 wrote:
>---------------------------
>>John Mann (xman52373@aol.com) on 7/7/10 wrote:
>>---------------------------
>>>While your article has merit, a few things you have over >looked. There is a water
>>>Simulation out using a 980X i7 CPU where all 12 core(6 real >and 6 virtual) are pegged
>>>at 100% and it still GETS trounced by a 9600GT running the >same simulation.
>>
>>That's quite possible, and I don't see how that is relevant. My point was primarily
>>about x87 vs. SSE usage and how that impacts the performance comparison between CPUs and GPUs.
>>
>>Multi-threading is a somewhat orthogonal issue, and as I pointed out - that is
>>left up to the developer for PhysX. Some developers are good and know what they
>>are doing. Some developers are not interested (or not capable) of writing high performance code.
>>
>>I don't doubt that there are cases where the GPU is much faster than the CPU.
>>I think Nvidia's done a good job of presenting some of those cases to the public.
>>
>>>A peformance
>>>differnce of around 10x if I recall correctly. And the >code run on the i7 was changed
>>>to run SSE code paths. So the boost could be seen, but the >GPU is and will always
>>>be magnitudes faster than CPU regardless of the code paths.
>>
>>There are definitely workloads where the GPU is dramatically faster than a CPU.
>>If you simply look at raw execution power for single precision, GPUs are often faster in theory and on paper.
>>
>>However, it really does depend on the algorithm you use, and how it's coded. Currently
>>vectorized SSE can provide up to a 4X boost over scalar SSE and probably a bit more
>>over x87. With AVX that will be an 8X boost.
>>
>>Multithreading can probably hit up to 4-8X, depending on the code being executed.
>>
>>There are a couple of papers I've seen that show at least a 25X variation in the
>>performance of various HPC workloads on a Nehalem due to tuning options.
>>
>>So I agree that for some workloads, GPUs will be faster, but it totally depends
>>on the workload, the algorithms and the coding style. I mean, nobody is trying
>>to execute a C compiler on a GPU, and there's a good reason for that.
>>
>>David
>
>While that is all well and good, your article does it best >to point out that PhysX
>can be done just as fast on the CPU as it is the GPU. >

No I didn't. I said that it it is possible to improve the performance of CPU PhysX, and the gains might be enough to make a difference.

>Problem here is Nvidia acknowledges
>that there are a few physics based situations where a GPU >can not be used and the
>physics work must be done by the CPU. But those that are >able to be run on the GPU,
>no matter the code optimazations made, will always be a >magnitude of 10 or more faster on the GPU vs the CPU.

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.

Moreover, it depends on how many cores in the CPU you can use, and how many cores in the GPU you can use. Some PhysX code may only use 1-2 cores (on Fermi).

>And softbodies is I believe but one of 2 or 3 that are >better suited for CPU use
>and not GPU. And interestingly enough, that is what you >used in your paper. So it
>is as if you are going out of your way to make Nvidia look >very bad when there is no need to.

I grabbed softbodies and cryostasis because they were convenient and easy, not out of any malice.

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