Haskell Compilation Improvement

By: anon (anon.delete@this.anon.com), April 11, 2013 7:14 am
Room: Moderated Discussions
Eric Bron (eric.bron.delete@this.zvisuel.privatefortest.com) on April 11, 2013 3:58 am wrote:
> > It is possible that future advances in CPU architectures and (more likely) compilers will surprise
> > you in a different way. Your sentence "I wouldn't be surprised if all the wins from software
> > prefetching go away, while the downsides remain" may turn out to be shortsighted.
>
> IMO there is some fundamental reasons against explicit software prefetch (besides the fact
> that hw prefetchers render it redundant in most situations), from the top of my head:
>
> 1) It is basically a single thread thing

What does this mean?

Single thread performance is very important quality, and increasingly it is reliant on software to get improvements.

Prefetch schemes that waste memory bandwidth or rely on exact size of cache may not be suited to multi thread situations, but that does not mean they are not suitable ever, or that they are the only schemes available.

Prefetching can help a bit when traversing data structures which are not contiguous in memory or at a predictable stride. Linked lists, trees, etc.

>
> 2) the IPC * clock frequency vs system memory latency wall, IPC * clock progress much faster than
> memory latency so you have to use higher and higher prefetch scheduling distances, you can use a
> variable offset (based on a training phase at startup) instead of a constant to make it future proof,
> but the hard fact is that the distance grow so much that you end up missing prefetch for the 1st
> iterations of your loops and wasting memory bandwidth for elements beyond your arrays

Prefetching can help to get improved memory level parallelism, and latency does not have to be completely hidden in order to be of help.

And prefetching of such simple strides over simple source data of big models has not been a good idea for years on "big" CPUs. Prefetch should be used on tricky cases.

Intel just added prefetchw, unsurprisingly it is much more suited to the case of iterating over more complex data structures (in which case you often want to apply some transformation to objects).
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TopicPosted ByDate
Haskell Compilation ImprovementSymmetry2013/04/09 10:41 AM
  Haskell Compilation ImprovementEric Bron2013/04/09 11:56 AM
  Haskell Compilation ImprovementLinus Torvalds2013/04/09 12:03 PM
    Haskell Compilation ImprovementEduardoS2013/04/09 12:20 PM
      Haskell Compilation ImprovementLinus Torvalds2013/04/09 12:31 PM
        Haskell Compilation ImprovementEduardoS2013/04/09 12:49 PM
    Haskell Compilation Improvement2013/04/11 01:36 AM
      Haskell Compilation ImprovementEric Bron2013/04/11 03:58 AM
        Haskell Compilation ImprovementBrendan2013/04/11 07:06 AM
          Haskell Compilation ImprovementSymmetry2013/04/11 07:45 AM
            Haskell Compilation ImprovementBrendan2013/04/11 11:31 AM
          Haskell Compilation ImprovementEric Bron2013/04/11 08:57 AM
            Haskell Compilation ImprovementBrendan2013/04/11 11:26 AM
              Haskell Compilation ImprovementEric Bron2013/04/11 11:36 AM
                Haskell Compilation ImprovementBrendan2013/04/11 05:00 PM
                  Haskell Compilation ImprovementDavid Kanter2013/04/11 08:50 PM
                    Software prefetching in JVMsGabriele Svelto2013/04/12 03:31 PM
                  Haskell Compilation ImprovementEric Bron2013/04/12 09:12 AM
                    Haskell Compilation ImprovementBrendan2013/04/12 11:40 AM
                      Haskell Compilation ImprovementEric Bron2013/04/12 12:15 PM
                        Haskell Compilation ImprovementBrendan2013/04/12 03:34 PM
                          Haskell Compilation ImprovementEric Bron2013/04/12 10:44 PM
                            Haskell Compilation ImprovementBrendan2013/04/13 02:20 AM
                              Haskell Compilation ImprovementEric Bron2013/04/13 02:32 AM
                                Haskell Compilation ImprovementBrendan2013/04/13 10:18 AM
                                  Haskell Compilation ImprovementEric Bron2013/04/14 01:04 AM
                          Haskell Compilation ImprovementEric Bron2013/04/15 08:34 AM
                            Haskell Compilation ImprovementBrendan2013/04/16 03:26 PM
                              Prefetch compilation testsEric Bron2013/04/21 12:52 AM
        Haskell Compilation Improvementanon2013/04/11 07:14 AM
          Haskell Compilation ImprovementMichael S2013/04/11 07:27 AM
            Haskell Compilation Improvementanon2013/04/11 08:25 AM
              Haskell Compilation ImprovementMichael S2013/04/11 08:37 AM
                Haskell Compilation Improvementbakaneko2013/04/11 09:39 AM
                  Haskell Compilation ImprovementEric Bron2013/04/11 10:08 AM
                    Haskell Compilation Improvementbakaneko2013/04/11 10:36 AM
                    Haskell Compilation Improvementanon2013/04/11 10:54 AM
                      Haskell Compilation ImprovementEric Bron2013/04/11 11:10 AM
                        Haskell Compilation Improvementanon2013/04/11 11:18 AM
                          Haskell Compilation ImprovementEric Bron2013/04/11 11:27 AM
                            Haskell Compilation Improvementanon2013/04/11 12:02 PM
                              Haskell Compilation ImprovementEric Bron2013/04/11 12:09 PM
                                Haskell Compilation ImprovementEric Bron2013/04/11 12:12 PM
                                Haskell Compilation Improvementanon2013/04/11 12:14 PM
                                  Haskell Compilation ImprovementEric Bron2013/04/11 12:30 PM
                                    Haskell Compilation Improvementanon2013/04/11 11:30 PM
                                      Haskell Compilation ImprovementEric Bron2013/04/12 09:25 AM
                                        Haskell Compilation Improvementanon2013/04/12 07:12 PM
                                          Haskell Compilation ImprovementEric Bron2013/04/12 10:51 PM
                                  Prefetch *hints*Konrad Schwarz2013/04/12 08:24 AM
                        Haskell Compilation ImprovementLinus Torvalds2013/04/11 12:56 PM
                          Inherent advantage of software prefetchJouni Osmala2013/04/11 09:41 PM
                            Inherent advantage of software prefetchSeni2013/04/13 03:40 AM
                            Another example: software scatter gather (NT)Megol2013/04/14 02:39 AM
                          Haskell Compilation ImprovementMaynard Handley2013/12/31 05:26 PM
                            Haskell Compilation ImprovementTREZA2013/12/31 05:44 PM
                              Haskell Compilation ImprovementMaynard Handley2013/12/31 07:49 PM
                                Haskell Compilation Improvementanon2013/12/31 10:39 PM
                                  Haskell Compilation ImprovementMaynard Handley2014/01/01 02:04 AM
                                  Haskell Compilation Improvementbakaneko2014/01/01 05:31 AM
                                Haskell Compilation ImprovementGabriele Svelto2014/01/02 07:57 AM
                                  Haskell Compilation ImprovementMichael S2014/01/02 08:37 AM
                                    Haskell Compilation ImprovementGabriele Svelto2014/01/02 10:09 AM
                                    Haskell Compilation ImprovementTREZA2014/01/02 12:43 PM
                            Haskell Compilation ImprovementMaynard Handley2013/12/31 06:07 PM
                            Future core architectures. (Was Haskell Compilation Improvement)Maynard Handley2014/01/03 12:06 AM
                              Speculative multi-threadingDavid Kanter2014/01/03 02:12 AM
                                Speculative multi-threadingMaynard Handley2014/01/03 05:01 AM
                              Future core architectures. (Was Haskell Compilation Improvement)Seni2014/01/03 01:09 PM
                              Future core architectures. (Was Haskell Compilation Improvement)Linus Torvalds2014/01/03 01:27 PM
                            Haskell Compilation ImprovementKonrad Schwarz2014/01/04 09:38 AM
              Haskell Compilation ImprovementEric Bron2013/04/11 09:23 AM
          Haskell Compilation ImprovementEric Bron2013/04/11 08:50 AM
            Haskell Compilation ImprovementEugene Nalimov2013/04/11 09:20 AM
              Haskell Compilation ImprovementEric Bron2013/04/11 09:28 AM
                Haskell Compilation ImprovementEduardoS2013/04/11 07:30 PM
            Haskell Compilation Improvementanon2013/04/11 10:19 AM
              Haskell Compilation ImprovementEric Bron2013/04/11 10:30 AM
                Haskell Compilation Improvementanon2013/04/11 10:50 AM
                  Haskell Compilation ImprovementEric Bron2013/04/11 11:03 AM
                    Haskell Compilation Improvementanon2013/04/11 11:16 AM
                      Haskell Compilation ImprovementEric Bron2013/04/11 11:24 AM
                        Haskell Compilation Improvementanon2013/04/11 12:09 PM
                          Haskell Compilation ImprovementEric Bron2013/04/11 12:43 PM
                            Haskell Compilation Improvementanon2013/04/11 11:27 PM
                              Haskell Compilation ImprovementEric Bron2013/04/12 12:15 AM
                                Haskell Compilation Improvementanon2013/04/12 07:14 PM
                                  Haskell Compilation ImprovementEric Bron2013/04/12 11:01 PM
                      Haskell Compilation ImprovementLinus Torvalds2013/04/11 01:05 PM
                        Haskell Compilation Improvementanon2013/04/11 10:42 PM
                        Haskell Compilation ImprovementRobert David Graham2013/04/12 02:12 PM
        Software prefetch architecturePaul A. Clayton2013/04/11 08:54 AM
          Software prefetch architectureEric Bron2013/04/11 09:06 AM
            Software prefetch architectureMegol2013/04/15 11:03 AM
              Software prefetch architectureEric Bron2013/04/15 11:30 AM
  low barMichael S2013/04/09 04:38 PM
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