ICL065: move elimination broken in Ice Lake

By: Travis Downs (travis.downs.delete@this.gmail.com), March 6, 2021 12:00 am
Room: Moderated Discussions
To work around an erratum, it looks like move elimination has been disabled in Ice Lake, at least as far back as the November microcode update (surprised nobody noticed until now).

I guess this might regress some workloads by a few %.

If anyone has TGL or any other post-ICL hardware, you could test this out by running uarch-bench like so:


./uarch-bench.sh --test-name=misc/mov-elim*
./uarch-bench.sh --timer=perf --extra-events=uops_executed.core --test-name=misc/mov-elim*


The second version uses perf and gives extra-definitive confirmation (but requires perf paranoid to be set up and rdpmc access, so sometimes is a bit trickier: try running as root).

Results like so indicate no elimination (smaller numbers indicate elimination):


** Running group misc : Miscellaneous tests **
Benchmark Cycles uops_e
8 chained moves 7.99 9.00
8 chained movs and inc 8.00 9.00
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ICL065: move elimination broken in Ice LakeTravis Downs2021/03/06 12:00 AM
  ICL065: move elimination broken in Ice LakeTravis Downs2021/03/06 12:01 AM
    ICL065: move elimination broken in Ice Lakeanon2021/03/06 01:41 AM
      ICL065: move elimination broken in Ice LakeTravis Downs2021/03/06 02:02 AM
        ICL065: move elimination broken in Ice LakeAndreas Abel2021/03/06 08:25 AM
    ICL065: move elimination broken in Ice LakeAndreas Abel2021/03/06 08:21 AM
      ICL065: move elimination broken in Ice Lakeanon2021/03/07 04:21 AM
        ICL065: move elimination broken in Ice Lakedmcq2021/03/07 11:15 AM
        ICL065: move elimination broken in Ice LakeTravis Downs2021/03/07 06:49 PM
          ICL065: move elimination broken in Ice Lakeanon2021/03/08 02:44 AM
            ICL065: move elimination broken in Ice LakeTravis Downs2022/06/27 09:27 PM
  ICL065: move elimination broken in Ice LakeJan Olšan2021/03/11 05:23 PM
    ICL065: move elimination broken in Ice LakeTravis Downs2021/03/11 10:07 PM
      ICL065: move elimination broken in Ice Lakeanonymou52021/03/12 03:37 AM
        ICL065: move elimination broken in Ice LakeTravis Downs2021/03/12 04:28 AM
  ICL065: move elimination broken in Ice LakeAndrey2021/03/22 04:20 AM
    ICL065: move elimination broken in Ice LakeRonald Maas2021/04/04 08:12 AM
      ICL065: move elimination broken in Ice LakeAndreas Abel2021/06/04 11:24 AM
        ICL065: move elimination broken in Ice LakeAndrey2021/06/04 01:21 PM
          ICL065: move elimination broken in Ice LakeAndreas Abel2021/06/04 02:32 PM
    ICL065: move elimination broken in Ice LakeClinton Ingram2021/08/26 06:18 PM
      ICL065: move elimination broken in Ice Laketarlinian2021/08/26 07:02 PM
        ICL065: move elimination broken in Ice Lakeanonymou52021/08/27 12:14 AM
          ICL065: move elimination broken in Ice LakeClinton Ingram2021/08/29 10:47 PM
            ICL065: move elimination broken in Ice Lakeanonymou52021/08/30 01:20 AM
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