AMD Compute and Texture Fetch

Article: Predicting AMD and Nvidia GPU Performance
By: David Kanter (dkanter.delete@this.realworldtech.com), April 22, 2011 10:53 am
Room: Moderated Discussions
Vincent Diepeveen (diep@xs4all.nl) on 4/22/11 wrote:
---------------------------
>David Kanter (dkanter@realworldtech.com) on 4/21/11 wrote:
>---------------------------
>>EduardoS (no@spam.com) on 4/20/11 wrote:
>>---------------------------
>>>Heikki Kultala (hkultala@iki.NOSPAM.fi) on 4/20/11 wrote:
>>>---------------------------
>>>>Texture fetches consume the execution slots of the >instruction word, ALU operations
>>cannot be started at same >cycle.
>>>
>>>No they don't, they are even on different clauses, the only >memory-like operation
>>>that consumes ALU slots is the LDS load/store, starting with >Evergreen, on R700 it was executed on TMUs too.
>>
>>My understanding (http://www.realworldtech.com/page.cfm?ArticleID=RWT121410213827&p=7)
>>is that on Cayman and Cypress, the ALUs are used for address calculations. So you
>>cannot simultaneously execute ALU clauses and initiate a texture fetch. However,
>>initiating a texture fetch is fairly quick - most of the time is spent waiting for
>>data. While you are waiting for data, the ALUs are free for independent computations.
>>
>>David
>
>Texture memory is not the adviced method to get things >done as texture memory is
>not so fast (though faster than main memory).

Well there aren't many other options besides the register file and local data store.

>In the first place you need to split up your software in >wavefronts that realistically
>only calculate within the compute units and don't use any >resources outside of it.
>
>Please note your artice is one of the few on the internet >which describes the Cayman architecture a bit.

Thank you for the compliment!

>The interesting thing to know obviously now is when AMD >has managed to fully improve
>the opencl compiler to support this new architecture >pretty well.
>
>Nvidia also seems to struggle supporting OpenCL well. This >where OpenCL really seems like an interesting thing.

I think NV probably has quite good OpenCL support, since they are basically just re-using a lot of their CUDA work.

>As for AMD gpu's, only opencl will get kept supported by >AMD for their GPU's, so there are not really choices there.

AMD also has CPU support.

>Beforehand OpenCL doesn't really seem like the perfect language yet, as a big droop
>for some will be that the current opencl 1.1 specs give 25% of the RAM as the maximum
>object size, which has the implication you can allocate only 25% for that whereas
>there will be several applications that want from this >tiny amount of RAM of course everything.

What OpenCL restriction are you thinking of? I haven't seen anything like that before (but I wasn't looking either).

>Yet it is a big step forward if you think about it how the entire HPC world will
>be supporting OpenCL and how also the other manufacturers will in the end be forced
>to produce hardware that uses the manycore concept, as this is seemingly (to hardware
>laymen like me) the only concept that will give enough >crunching power at a cheap price in the close future.

GPUs don't have that many cores. They are still at around ~10-20, but they use vectorization and VLIW to achieve a higher number of FLOP/core than a traditional CPU.

Honestly, Tilera has more cores than any GPU.

>Of course the compiler quality will be very important then.
>
>There is a lot to win there, for example having logics in >the compiler to recognize
>whether the programmer is trying to use the actual carry, >caused for example by
>an overflow adding 2 (unsigned) integers.

Compiler quality is always a significant factor!

David
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TopicPosted ByDate
New Article: Predicting GPU Performance for AMD and NvidiaDavid Kanter2011/04/11 11:55 PM
  Graph is not red-green colorblind friendly (NT)RatherNotSay2011/04/12 03:51 AM
    FixedDavid Kanter2011/04/12 08:46 AM
  New Article: Predicting GPU Performance for AMD and NvidiaJames2011/04/12 12:30 PM
    New Article: Predicting GPU Performance for AMD and NvidiaDavid Kanter2011/04/12 02:51 PM
  Try HD6450 or HD6850EduardoS2011/04/12 03:31 PM
    Try HD6450 or HD6850David Kanter2011/04/13 10:25 AM
      Try HD6450 or HD6850EduardoS2011/04/13 03:20 PM
        of causeMoritz2011/04/14 08:03 AM
          of causeEduardoS2011/04/14 01:55 PM
            Barts = 5DMoritz2011/04/14 09:26 PM
              Barts = 5DAntti-Ville Tuunainen2011/04/15 12:38 AM
                Limiting fixed function unitsMoritz2011/04/15 04:28 AM
                  Limiting fixed function unitsVincent Diepeveen2011/04/20 02:38 AM
                    lack of detailMoritz2011/04/20 09:24 AM
                      lack of detailEduardoS2011/04/20 11:45 AM
            gpgpuVincent Diepeveen2011/04/16 02:10 AM
              gpgpuEduardoS2011/04/17 12:31 PM
                gpgpuGroo2011/04/17 12:58 PM
                  gpgpuEduardoS2011/04/17 01:08 PM
                  gpgpuIan Ameline2011/04/18 03:55 PM
                    gpgpuPing-Che Chen2011/04/19 12:59 AM
                      GPU numerical complianceSylvain Collange2011/04/19 11:38 AM
                        GPU numerical complianceVincent Diepeveen2011/04/20 02:17 AM
                gpgpuVincent Diepeveen2011/04/20 02:02 AM
                  gpgpu and core countsHeikki Kultala2011/04/20 04:41 AM
                    gpgpu and core countsVincent Diepeveen2011/04/20 05:52 AM
                      gpgpu and core countsnone2011/04/20 07:05 AM
                        gpgpu and core countsEduardoS2011/04/20 11:36 AM
                      gpgpu and core countsHeikki Kultala2011/04/20 10:16 AM
                        gpgpu and core countsEduardoS2011/04/20 11:34 AM
                          gpgpu and core countsHeikki Kultala2011/04/20 07:24 PM
                            gpgpu and core countsEduardoS2011/04/20 08:55 PM
                              gpgpu and core countsHeikki Kultala2011/04/21 06:48 AM
                                gpgpu and core countsEduardoS2011/04/22 01:41 PM
                              AMD Compute and Texture FetchDavid Kanter2011/04/21 10:42 AM
                                AMD Compute and Texture FetchVincent Diepeveen2011/04/22 01:14 AM
                                  AMD Compute and Texture FetchDavid Kanter2011/04/22 10:53 AM
                                AMD Compute and Texture FetchEduardoS2011/04/22 01:46 PM
                                  AMD Compute and Texture FetchDavid Kanter2011/04/22 02:02 PM
                                    AMD Compute and Texture FetchEduardoS2011/04/22 02:18 PM
                                    AMD Compute and Texture Fetchanon2011/04/22 03:30 PM
                                      AMD Compute and Texture FetchDavid Kanter2011/04/22 09:17 PM
                        gpgpu and core countsVincent Diepeveen2011/04/20 12:12 PM
                          gpgpu and core countsHeikki Kultala2011/04/21 10:23 AM
                            gpgpu and core countsVincent Diepeveen2011/04/22 02:11 AM
                              Keep the crazy politics out of thisDavid Kanter2011/04/22 08:39 AM
                                Keep the crazy politics out of thisVincent Diepeveen2011/04/22 09:12 AM
                                  Keep the crazy politics out of thisDavid Kanter2011/04/22 10:44 AM
                              gpgpu and core countsJouni Osmala2011/04/22 11:06 AM
                  gpgpuEduardoS2011/04/20 11:59 AM
                    gpgpuVincent Diepeveen2011/04/20 12:37 PM
                      gpgpuEduardoS2011/04/20 05:27 PM
                        gpgpuVincent Diepeveen2011/04/21 02:06 AM
                          gpgpuEduardoS2011/04/22 02:00 PM
  New Article: Predicting GPU Performance for AMD and NvidiaPiedPiper2011/04/12 10:05 PM
    New Article: Predicting GPU Performance for AMD and NvidiaDavid Kanter2011/04/12 10:42 PM
      New Article: Predicting GPU Performance for AMD and NvidiaMS2011/04/15 05:04 AM
        New Article: Predicting GPU Performance for AMD and NvidiaKevin G2011/04/16 02:25 AM
          New Article: Predicting GPU Performance for AMD and NvidiaDavid Kanter2011/04/16 08:42 AM
          New Article: Predicting GPU Performance for AMD and NvidiaVincent Diepeveen2011/04/20 02:20 AM
    memoryMoritz2011/04/14 09:03 PM
      memory - moreMoritz2011/04/15 11:11 PM
  New Article: Predicting GPU Performance for AMD and NvidiaKevin G2011/04/14 11:30 AM
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