Interesting comment about rep instructions & code size

By: none (none.delete@this.none.com), January 15, 2020 8:59 am
Room: Moderated Discussions
Gabriele Svelto (gabriele.svelto.delete@this.gmail.com) on January 15, 2020 6:12 am wrote:
>
Rather than tune for individual microarchitecture variations, we would prefer to leverage on fast string
> operations provided by the ISA (for example “rep movsb” on x86). This allows us to leverage wider
> data paths over time, without having to build custom dispatch logic which carries its own overheads.
>
>


I guess this works well for them because their machines have rather recent CPU with
decent speed for rep movs, and they can put enough pressure on Intel to ensure that rep
movs speed won't degrade over time (something I think would not happen anyway).

I mean could average JoeDev assume using rep movs in his code will be efficient on most
of the end user machines some of which could be somewhat old?

I wonder if someone collected data about performance of rep movs/stos depending on the
micro-architecture. I guess Linus has such data, but is that publicly available?

> And also
>
>
Small Code Footprint: Our implementations consist of concise patterns for working with chunks
> of data. While further specialization can produce better results on microbenchmarks, we did
> not see these wins materialize on macrobenchmarks measuring application productivity.
>
>


I have seen people trying to prove their memcpy was the best one by running in a loop all
the memcpy found in some benchmark (such as SPEC gcc). Frightening.
< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
LLVM comments on mem*Maynard Handley2020/01/14 01:51 PM
  LLVM comments on mem*Anon32020/01/15 06:28 AM
  Interesting comment about rep instructions & code sizeGabriele Svelto2020/01/15 07:12 AM
    Interesting comment about rep instructions & code sizenone2020/01/15 08:59 AM
      Interesting comment about rep instructions & code sizeGabriele Svelto2020/01/16 03:56 AM
        Interesting comment about rep instructions & code sizeLinus Torvalds2020/01/16 10:12 AM
          ISA support for constant count loopsPaul A. Clayton2020/01/16 11:28 AM
            ISA support for constant count loopsGabriele Svelto2020/01/16 02:15 PM
              PowerPC "front-end registers"Paul A. Clayton2020/01/16 03:34 PM
              ISA support for constant count loopsTravis Downs2020/01/16 05:21 PM
                ISA support for constant count loopsLinus Torvalds2020/01/16 08:41 PM
                  ISA support for constant count loopsTravis2020/01/16 09:48 PM
                    ISA support for constant count loopsBrett2020/01/17 01:28 AM
              Branch to CTRMaya2020/01/18 08:15 AM
                Branch to CTRGabriele Svelto2020/01/18 01:14 PM
            ISA support for constant count loopsanon2020/01/17 08:28 AM
              ISA support for constant count loopsTravis Downs2020/01/17 08:34 AM
            ISA support for constant count loops: ineffective compared to micro-threads2020/01/20 08:02 AM
              ISA support for constant count loops: ineffective compared to micro-threadssomeone2020/01/20 12:23 PM
                ISA support for constant count loops: ineffective compared to micro-threads2020/01/22 09:23 AM
              ISA support for too slow computersEtienne2020/01/21 02:42 AM
                ISA support for constant count loops: ineffective compared to micro-threads2020/01/22 09:18 AM
                  ISA support for constant count loops: ineffective compared to micro-threads2020/01/22 10:04 AM
                  ISA support for constant count loops: ineffective compared to micro-threadsHeikki Kultala2020/01/22 10:47 AM
                    ISA support for constant count loops: ineffective compared to micro-threadsdmcq2020/01/22 01:31 PM
                    ISA support for constant count loops: ineffective compared to micro-threads2020/01/22 03:28 PM
                      ISA support for constant count loops: ineffective compared to micro-threadsEtienne2020/01/22 04:35 PM
          Interesting comment about rep instructions & code sizeGabriele Svelto2020/01/16 02:00 PM
    Interesting comment about rep instructions & code sizeTravis Downs2020/01/15 03:40 PM
      Interesting comment about rep instructions & code sizeChester2020/01/15 05:16 PM
        Interesting comment about rep instructions & code sizeTravis Downs2020/01/15 05:50 PM
          Interesting comment about rep instructions & code sizeChester2020/01/15 07:24 PM
            Interesting comment about rep instructions & code sizeTravis Downs2020/01/16 02:26 PM
              Interesting comment about rep instructions & code sizeChester2020/01/17 01:16 PM
                Interesting comment about rep instructions & code sizeTravis Downs2020/01/17 03:41 PM
        Interesting comment about rep instructions & code sizeGabriele Svelto2020/01/16 03:53 AM
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