Intel might be moving from ISA to platform

Article: Parallelism at HotPar 2010
By: hobold (hobold.delete@this.vectorizer.org), August 26, 2010 3:37 am
Room: Moderated Discussions
Michael S (already5chosen@yahoo.com) on 8/23/10 wrote:
---------------------------
[...]
>There are good reasons to prefer single-threaded SIMD over MT scalar. First, the
>change is more "local", other parts of the application less influenced. Second,
>until Nehalem you often could gain more by SIMD than by threading. Third, fewer
>performance surprises due to effects of cache layout.
>Fourth, sometimes other parts of your application could effectively utilize the
>remaining cores. And finally, fifth, not everybody share the mentality of "grab
>as many computing resources as you can and other applications (or user on time sharing machine) can go to hell.
>
My favourite reason to sometimes like SIMD over concurrent threads is the fact that all vector lanes are processed in lockstep (or at least pretend to be). This can sometimes be used to exploit fine grain parallelism despite rather strong data dependencies.

As an example, think of a two dimensional image filter, where each pixel result depends on the left and top neighbours' result (except for the border, as usual). Any scalar implementation would probably just iterate over rows or columns, with a loop carried dependency. (Distance transforms might be the most relevant instance of this pattern.)

The "axis of parallelism" is diagonal, and a SIMD implementation could exploit that. Data dependencies would be handled by the sequential order in which individual vectors are being processed. A multithreaded implementation would need explicit synchronization to ensure that all required neighbours are available. You can't just start processing of row 2 after the row 1 thread has gotten enough of a head start.

(Yes, you can do SIMD and threading simultaneously. But the threading would not be fine grained, but on the level of larger tiles.)
< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
Tarek's Hotpar 2010 article onlineDavid Kanter2010/07/27 07:29 AM
  Tarek's Hotpar 2010 article onlineAnon2010/07/27 01:57 PM
    Tarek's Hotpar 2010 article onlineDavid Kanter2010/07/27 10:48 PM
      Tarek's Hotpar 2010 article onlineAnon2010/07/28 02:44 PM
        Tarek's Hotpar 2010 article onlineanon2010/07/28 04:10 PM
        CPU+GPUDavid Kanter2010/07/29 11:38 AM
          CPU+GPUMark Christiansen2010/07/30 06:36 AM
            CPU+GPUhobold2010/07/30 06:54 AM
              CPU+GPUGabriele Svelto2010/07/30 07:18 AM
                CPU+GPUhobold2010/07/30 02:46 PM
              CPU+GPUAaron Spink2010/08/02 05:32 PM
                CPU+GPUhobold2010/08/03 03:33 AM
                  CPU+GPURicardo B2010/08/03 04:19 AM
            CPU+GPU - the software problemVincent Diepeveen2010/07/31 04:50 PM
              CPU+GPU - the software problemmpx2010/08/02 11:19 AM
                CPU+GPU - the software problemRichard Cownie2010/08/02 12:48 PM
                  CPU+GPU - the software problemGabriele Svelto2010/08/02 11:10 PM
                    CPU+GPU - the software problemhobold2010/08/03 03:41 AM
                      CPU+GPU - the software problemRichard Cownie2010/08/03 05:17 AM
                        CPU+GPU - the software problemhobold2010/08/04 06:45 AM
                          NVidia in a holeRichard Cownie2010/08/04 07:23 AM
                            NVidia in a holeRohit2010/08/04 07:33 AM
                              NVidia in a holeRichard Cownie2010/08/04 07:50 AM
                                NVidia in a holeRohit2010/08/05 06:31 AM
                                  NVidia in a holeGroo2010/08/05 01:08 PM
                                NVidia in a holeGroo2010/08/05 01:07 PM
                              NVidia in a holeMark Roulo2010/08/04 08:26 AM
                                NVidia in a holeLaughabee2010/08/18 07:28 AM
                            Can nVidia survive without a sub-$100 GPU market?Mark Roulo2010/08/04 08:29 AM
                              Can nVidia survive without a sub-$100 GPU market?Richard Cownie2010/08/04 08:42 AM
                                Can nVidia survive without a sub-$100 GPU market?Mark Roulo2010/08/04 08:55 AM
                                  Can nVidia survive without a sub-$100 GPU market?Linus Torvalds2010/08/04 10:35 AM
                                    "profit" is subjectiveRichard Cownie2010/08/04 10:49 AM
                                      "profit" is subjectivea reader2010/08/06 03:54 AM
                                        no price warRichard Cownie2010/08/06 06:18 AM
                                  Can nVidia survive without a sub-$100 GPU market?Aaron Spink2010/08/04 11:19 AM
                                  Can nVidia survive without a sub-$100 GPU market?Konrad Schwarz2010/08/06 07:13 AM
                                CPU lineup != GPU lineupRohit2010/08/05 06:43 AM
                                  CPU lineup != GPU lineupRichard Cownie2010/08/05 07:12 AM
                                    CPU lineup != GPU lineupRohit2010/08/05 07:37 AM
                                      CPU lineup != GPU lineupRichard Cownie2010/08/05 07:56 AM
                                        CPU lineup != GPU lineupRohit2010/08/05 10:19 AM
                                          CPU lineup != GPU lineuphobold2010/08/06 03:08 AM
                                            CPU lineup != GPU lineupRohit2010/08/06 06:24 AM
                                              CPU lineup != GPU lineuphobold2010/08/06 06:41 AM
                              Can nVidia survive without a sub-$100 GPU market?David Hess2010/08/04 10:31 AM
                              Can nVidia survive without a sub-$100 GPU market?Ricardo B2010/08/04 12:16 PM
                              Semiconductor economicsDavid Kanter2010/08/05 08:13 AM
                                Semiconductor economicsRichard Cownie2010/08/05 08:51 AM
                                  NV buying ViA could shake up thingsRohit2010/08/05 10:09 AM
                                    NV buying ViA could shake up thingsRichard Cownie2010/08/05 10:25 AM
                                      Not likelyDavid Kanter2010/08/05 01:39 PM
                                        Not likelyrandom2010/08/05 01:49 PM
                                          Not likelyAaron Spink2010/08/05 02:18 PM
                                        Not likelyGroo2010/08/05 09:05 PM
                                        Not likelyRohit2010/08/06 06:25 AM
                                    NV buying ViA could shake up thingsGroo2010/08/05 09:02 PM
                                    NV buying ViA could shake up thingsehud2010/08/06 12:53 AM
                                      NV buying ViA could shake up thingsRohit2010/08/06 06:30 AM
                                        NV buying ViA could shake up thingsKevin G2010/08/06 04:54 PM
                                          ViA buying NV could shake up thingsBrendan2010/08/19 05:23 AM
                                        NV buying ViA could shake up thingsGroo2010/08/06 07:24 PM
                            NVidia in a holempx2010/08/04 11:01 AM
                              NVidia in a holeRichard Cownie2010/08/04 11:31 AM
                                NVidia in a holercf2010/08/04 02:40 PM
                              NVidia in a holeRohit2010/08/05 06:51 AM
                              NVidia in a holeGroo2010/08/05 08:50 PM
                              NVidia in a holeAaron Spink2010/08/05 10:52 PM
                          Anyone else wish Intel would buy Nvidia ? (NT)Silent2010/08/07 12:30 AM
                            Hell noa2010/08/07 07:37 PM
                        CPU+GPU - the software problemno thanks2010/08/04 06:54 PM
                          CPU+GPU - the software problemJouni Osmala2010/08/05 12:41 AM
                            CPU+GPU - the software problemIntelUser20002010/08/05 06:54 PM
                              CPU+GPU - the software problemJouni Osmala2010/08/05 08:36 PM
                            CPU+GPU - the software problemLinus Torvalds2010/08/06 07:08 AM
                              CPU+GPU - the software problemanonymous2010/08/06 08:39 AM
                                CPU+GPU - the software problemLinus Torvalds2010/08/06 09:56 AM
                                  non-existent Via+NV vs real OntarioRichard Cownie2010/08/06 11:12 AM
                              CPU+GPU - the software problemkoby m.2010/08/07 01:06 AM
                  CPU+GPU - the software problemhobold2010/08/03 03:48 AM
                CPU+GPU - the software problemhobold2010/08/03 03:45 AM
                  CPU+GPU - the software problemRichard Cownie2010/08/03 05:22 AM
          CPU+GPUAnon2010/07/30 08:11 PM
            CPU+GPUanon2010/07/31 02:19 AM
            CPU+GPUAaron Spink2010/08/02 05:45 PM
          100x speedups -- here we go againAM2010/08/02 12:37 AM
            100x speedups -- here we go againanon2010/08/02 02:32 AM
              100x speedups -- here we go againanon2010/08/02 10:14 PM
            GPU raw H/W only has about a 10x advantage over a CPUMark Roulo2010/08/02 08:41 AM
              GPU raw H/W only has about a 10x advantage over a CPUMichael S2010/08/02 02:31 PM
                GPU raw H/W only has about a 10x advantage over a CPUanon2010/08/02 08:36 PM
                  GPU raw H/W only has about a 10x advantage over a CPUMichael S2010/08/02 11:41 PM
                    GPU raw H/W only has about a 10x advantage over a CPUMark Roulo2010/08/03 07:22 AM
                      GPU raw H/W only has about a 10x advantage over a CPURohit2010/08/04 06:08 AM
                      There is reasonable explanation...Jouni Osmala2010/08/04 09:10 PM
                  GPU raw H/W only has about a 10x advantage over a CPUMark Roulo2010/08/03 07:19 AM
              simple reality check for youAM2010/08/03 12:45 AM
                simple reality check for younone2010/08/03 06:27 AM
                  simple reality check for youAM2010/08/03 10:50 PM
                    simple reality check for youanon2010/08/03 11:06 PM
                      simple reality check for youAM2010/08/05 02:51 AM
                        catch the same boat as everyone else next time (NT)anon2010/08/05 03:44 AM
                Simple reality checkDavid Kanter2010/08/03 07:24 AM
                  Simple reality checkGabriele Svelto2010/08/03 09:51 PM
                  Simple reality checkAM2010/08/03 10:57 PM
                    Simple reality checkanon2010/08/03 11:12 PM
                      Simple reality checkAM2010/08/05 02:59 AM
                        Simple reality checkanon2010/08/05 03:47 AM
                          Study the papers, troll (NT)AM2010/08/05 11:01 PM
                    Simple reality checkhobold2010/08/04 04:05 AM
                    Simple reality checkDean Kent2010/08/04 08:30 AM
                      Simple reality checkMark Roulo2010/08/04 08:59 AM
                      Suggestion for David Kanter and Mark RouloAM2010/08/05 02:57 AM
                        Suggestion for David Kanter and Mark Roulonone2010/08/05 03:22 AM
                          Suggestion for David Kanter and Mark RouloAM2010/08/05 11:04 PM
                        Suggestion for David Kanter and Mark Roulonone2010/08/05 03:38 AM
                          Suggestion for David Kanter and Mark Rouloanon2010/08/05 03:43 AM
                            Suggestion for David Kanter and Mark RouloAM2010/08/05 11:11 PM
                              Suggestion for David Kanter and Mark Rouloanon2010/08/06 06:52 AM
                          Suggestion for David Kanter and Mark RouloAM2010/08/05 11:10 PM
                            Suggestion for David Kanter and Mark Roulonone2010/08/06 12:35 AM
                              price doesn't matter only in theories (NT)AM2010/08/09 01:13 AM
                            Not apple4appleMichael S2010/08/06 04:13 AM
                              Not apple4appleAM2010/08/09 01:09 AM
                                Not apple4appleMichael S2010/08/09 03:35 AM
                                  Not apple4appleAM2010/08/10 12:05 AM
                                    Not apple4applenone2010/08/10 12:38 AM
                                      Back to topicAM2010/08/10 11:03 PM
                                      Final note (and some remarks on Intel's paper)AM2010/08/13 03:28 AM
                                        Final note (and some remarks on Intel's paper)none2010/08/13 08:10 AM
                                          Final note (and some remarks on Intel's paper)AM2010/08/16 12:14 AM
                                            Final note (and some remarks on Intel's paper)none2010/08/16 05:29 AM
                                              One example of 1000X shown to be wrong.sea2010/08/16 06:55 PM
                                                You're short of some factsAM2010/08/17 12:13 AM
                                                  Maybe you need to read beyond the PR statementSteve Underwood2010/08/17 01:39 AM
                                                    Maybe you need to read beyond the PR statementGroo2010/08/17 07:18 PM
                                                    check the hw they usedAM2010/08/18 02:33 AM
                                                Please realize what Monte Carlo meansVincent Diepeveen2010/08/18 02:28 AM
                                              Final note (and some remarks on Intel's paper)AM2010/08/17 12:18 AM
                                        Final note (and some remarks on Intel's paper)anon2010/08/14 12:22 AM
                                          Final note (and some remarks on Intel's paper)AM2010/08/16 12:15 AM
                                            Final note (and some remarks on Intel's paper)anon2010/08/16 01:10 PM
                                              Final note (and some remarks on Intel's paper)AM2010/08/17 12:15 AM
                                                Final note (and some remarks on Intel's paper)Michael S2010/08/17 01:58 AM
                                                  Final note (and some remarks on Intel's paper)AM2010/08/18 02:17 AM
                                                    Final note (and some remarks on Intel's paper)gallier22010/08/18 03:52 AM
                                                    Final note (and some remarks on Intel's paper)Michael S2010/08/18 04:33 AM
                                                      Final note (and some remarks on Intel's paper)Gabriele Svelto2010/08/18 05:11 AM
                                                      Final note (and some remarks on Intel's paper)Steve Underwood2010/08/18 03:03 PM
                                                        Intel might be moving from ISA to platformhobold2010/08/19 02:58 AM
                                                          Intel might be moving from ISA to platformSteve Underwood2010/08/22 06:00 PM
                                                            Intel might be moving from ISA to platformAnon2010/08/22 09:43 PM
                                                              Intel might be moving from ISA to platformajensen2010/08/22 11:37 PM
                                                                Intel might be moving from ISA to platformMichael S2010/08/23 01:13 AM
                                                                  Intel might be moving from ISA to platformSteve Underwood2010/08/23 01:35 AM
                                                                  Intel might be moving from ISA to platformhobold2010/08/26 03:37 AM
                                                                Intel might be moving from ISA to platformAnon2010/08/23 02:47 PM
                                                              Intel might be moving from ISA to platformSteve Underwood2010/08/23 01:25 AM
                                                                Intel might be moving from ISA to platformhobold2010/08/23 02:03 AM
                                                                  Intel might be moving from ISA to platformSteve Underwood2010/08/23 03:26 AM
                                                                Intel might be moving from ISA to platformAnon2010/08/23 02:55 PM
                                                                Intel might be moving from ISA to platformrwessel2010/08/23 05:41 PM
                                                                  Intel might be moving from ISA to platformSteve Underwood2010/08/23 06:30 PM
                                                                    Intel might be moving from ISA to platformrwessel2010/08/23 08:50 PM
                                                                      Intel might be moving from ISA to platformSteve Underwood2010/08/23 09:34 PM
                                                                        Intel might be moving from ISA to platformrwessel2010/08/24 12:03 AM
                                                              Intel might be moving from ISA to platformIan Ollmann2010/08/23 08:21 PM
                                                          Intel might be moving from ISA to platformajensen2010/08/22 09:36 PM
                                                            Intel might be moving from ISA to platformIan Ollmann2010/08/23 08:45 PM
                                                      Final note (and some remarks on Intel's paper)AM2010/08/19 12:29 AM
                                                        Final note (and some remarks on Intel's paper)Richard2010/08/19 03:51 AM
                                                          I stand corrected.Michael S2010/08/19 04:30 AM
                simple reality check for youanonymous2010/08/03 09:25 AM
                  simple reality check for youAM2010/08/03 10:47 PM
                    simple reality check for youanonymous2010/08/04 09:17 AM
                      simple reality check for youanon2010/08/04 07:33 PM
                      SPECint/FPAM2010/08/05 02:49 AM
                  simple reality check for youRohit2010/08/13 07:31 PM
                    simple reality check for youhobold2010/08/16 05:29 AM
              maybe texture caches ?Richard Cownie2010/08/03 08:27 AM
                maybe texture caches ?none2010/08/03 08:59 AM
                  maybe texture caches ?Richard Cownie2010/08/03 09:15 AM
                    maybe texture caches ?Mark Roulo2010/08/03 09:23 AM
                      maybe texture caches ?Richard Cownie2010/08/03 09:33 AM
                        maybe texture caches ?Mark Roulo2010/08/03 09:37 AM
                          the Hess paperRichard Cownie2010/08/03 10:16 AM
                    maybe texture caches ?Aaron Spink2010/08/03 12:23 PM
                      maybe texture caches ?Mark Roulo2010/08/03 03:13 PM
                        maybe texture caches ?Michael S2010/08/04 12:47 AM
                  maybe texture caches ?Michael S2010/08/03 09:23 AM
                maybe texture caches ?Mark Roulo2010/08/03 09:19 AM
                  maybe texture caches ?Richard Cownie2010/08/03 09:42 AM
                Cache to cache comparisonDavid Kanter2010/08/03 11:28 AM
                  Cache to cache comparisonRichard Cownie2010/08/03 11:52 AM
                    Cache to cache comparisonDavid Kanter2010/08/03 12:21 PM
                      Cache to cache comparisonRichard Cownie2010/08/03 02:55 PM
                      Cache to cache comparisonGabriele Svelto2010/08/03 10:23 PM
                        Nehalem vs Core2Richard Cownie2010/08/04 03:24 PM
                          Nehalem vs Core2IntelUser20002010/08/04 06:26 PM
                          Nehalem vs Core2Gabriele Svelto2010/08/04 09:51 PM
                            Nehalem vs Core2Richard Cownie2010/08/05 02:27 AM
                              Nehalem vs Core2Gabriele Svelto2010/08/05 05:00 AM
                                Nehalem vs Core2Richard Cownie2010/08/05 06:10 AM
                                  Nehalem vs Core2Gabriele Svelto2010/08/05 06:41 AM
                                    Nehalem vs Core2Michael S2010/08/05 09:02 AM
                              Nehalem vs Core2Michael S2010/08/05 09:12 AM
                          Nehalem vs Core2Michael S2010/08/04 11:36 PM
                            Nehalem vs Core2Richard Cownie2010/08/05 07:33 AM
                              Nehalem vs Core2Michael S2010/08/05 08:44 AM
                                Nehalem vs Core2Richard Cownie2010/08/05 09:03 AM
                                  Nehalem vs Core2Michael S2010/08/05 03:21 PM
                                    Nehalem vs Core2Richard Cownie2010/08/05 06:15 PM
                                      I'm wrong, you're right - i's 2 dieRichard Cownie2010/08/05 06:21 PM
                                    Nehalem vs Core2Richard Cownie2010/08/06 07:12 AM
                                      Nehalem vs Core2Michael S2010/08/06 07:33 AM
                                      Nehalem L1 cache latency a hedge for higher clock speeds?Mark Roulo2010/08/06 07:36 AM
                                        Nehalem L1 cache latency a hedge for higher clock speeds?Kevin G2010/08/07 09:14 AM
                                          Nehalem L1 cache latency a hedge for higher clock speeds?IntelUser20002010/08/07 01:32 PM
                                        Nehalem L1 cache latency a hedge for higher clock speeds?someone2010/08/07 01:35 PM
                          difference between C2D/C2Q chipsetsMichael S2010/08/04 11:57 PM
                          Nehalem core goals ... my takeMark Roulo2010/08/06 06:53 AM
                            Bulldozer single-threadRichard Cownie2010/08/06 03:05 PM
                          Nehalem vs Core2Carlie Coats2010/08/07 07:41 AM
                            scalingMichael S2010/08/07 10:12 AM
                            why X5460?Michael S2010/08/07 10:12 AM
                              why X5460?Carlie Coats2010/08/08 03:34 AM
                                why X5460?Michael S2010/08/08 03:42 AM
                                  Polling/PIO based COMM libraries?Michael S2010/08/08 04:14 AM
                    Cache to cache comparisonAnts Aasma2010/08/04 09:00 AM
                      Cache to cache comparisonRichard Cownie2010/08/04 09:08 AM
                        Cache to cache comparisonAnts Aasma2010/08/04 10:28 AM
                      Cache to cache comparisonMichael S2010/08/04 10:33 AM
                        Cache to cache comparisonMark Roulo2010/08/04 11:29 AM
                          Cache to cache comparisonAnts Aasma2010/08/04 12:10 PM
                            Fermi and G200 instruction latencyMark Roulo2010/08/04 01:10 PM
                              Fermi and G200 instruction latencyAnts Aasma2010/08/04 02:01 PM
                        Cache to cache comparisonAnts Aasma2010/08/04 12:00 PM
                        Register read comparisonDavid Kanter2010/08/05 08:16 AM
                          Register read comparisonGabriele Svelto2010/08/05 10:42 PM
                maybe texture caches ?Aaron Spink2010/08/03 12:17 PM
              GPU raw H/W only has about a 10x advantage over a CPURichard2010/08/09 03:58 AM
                GPU raw H/W only has about a 10x advantage over a CPUnone2010/08/09 04:19 AM
                  GPU raw H/W only has about a 10x advantage over a CPUVincent Diepeveen2010/08/24 06:18 AM
                    Forget it, they won't hear itanon2010/08/24 03:37 PM
                    GPU raw H/W only has about a 10x advantage over a CPURichard2010/08/25 12:03 PM
                This forum supports pre tagMichael S2010/08/09 05:03 AM
    Tarek's Hotpar 2010 article onlineRich Vuduc2010/07/28 09:24 AM
      Tarek's Hotpar 2010 article onlineAnon2010/07/28 03:18 PM
  Low hanging fruitMoritz2011/02/03 11:20 AM
    Low hanging fruitJukka Larja2011/02/06 04:01 AM
Reply to this Topic
Name:
Email:
Topic:
Body: No Text
How do you spell green?