Intel is cheating AnTuTu

By: Wilco (Wilco.Dijkstra.delete@this.ntlworld.com), July 17, 2013 3:46 pm
Room: Moderated Discussions
bakaneko (nyan.delete@this.hyan.wan) on July 16, 2013 4:55 am wrote:
> ⚛ (0xe2.0x9a.0x9b.delete@this.gmail.com) on July 16, 2013 3:16 am wrote:
> > Linus Torvalds (torvalds.delete@this.linux-foundation.org) on July 15, 2013 8:45 pm wrote:
> > > bakaneko (nyan.delete@this.hyan.wan) on July 15, 2013 7:47 pm wrote:
> > > >
> > > > As someone who works for ARM as compiler writer,
> > > > why don't you tell us in more detail how Intel
> > > > cheated?
> > >
> > > Exophase's post to anandtech was quoted here earlier, I think. It has the relevant details:
> > >
> > > http://forums.anandtech.com/showthread.php?t=2330027
> > >
> > > and quite frankly, while optimizing multiple bit operations into a word is a very
> > > valid optimization, the code icc generates there seems a fair bit past that.
> > >
> > > Sure, it could in theory happen with a really smart compiler and lots of generic optimizations.
> > > In practice? It really smells like the compiler actively targeting a very particular code-sequence.
> > > IOW, compiler cheating. The timing that Exophase points out makes it look worse.
> > >
> > > And Wilco is right that it smells pretty bad when AnTuTu seems to be so close to
> > > intel, and seem to have bent over backwards using recent versions of icc etc.
> > >
> > > It's all "explainable". But it doesn't pass the smell test.
> > >
> > > Linus
> >
> > The optimization is clearly doable by a machine. In my opinion this means there is no reason to criticize
> > the compiler or the compiler team for adding the optimization to the compiler. The blame should go towards
> > people who published the benchmark results without making it clear that the results are a mixture of
> > raw CPU performance and compiler optimizations in the context of a particular benchmark.
> >
> > It isn't compiler cheating. It is misattribution of benchmark results. The improved benchmark numbers
> > should have been attributed to both the CPU and the compiler, rather than just to the CPU alone.
> >
> > I think it would be best for benchmarks to take into account
> > the number of executed instructions. Seeing the
> > numbers of executed instructions when comparing benchmarks
> > would make it easier to distinguish CPU performance
> > from compiler performance (and from other stuff). It would
> > be nice for this to become the standard way of reporting
> > benchmarks by benchmarking sites. It would be interesting to see similar numbers in GPU benchmarks.
>
> The question is how this benchmark got ever
> published like this. Some people assume it
> was done by malice.
>
> If it was only about the benchmark, then the
> benchmark is clearly at fault because it uses
>
> typedef unsigned long farulong;
>
> but never prefixes it with volatile (I think
> this was enough in this case) in ToggleBitRun,
> so the compiler can run wild with merging
> memory accesses.

Remember this is 20 year old code - compilers were pretty dumb, volatile was new and practically unused/unknown. ByteMark never gained much popularity, it disappeared as quickly as it emerged - I never imagined that someone would use it as a mobile benchmark. By far the best solution is to never use this code, especially not as a RAM benchmark...

Wilco
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ARM at Computexanon2013/06/03 08:54 AM
  ARM at ComputexExophase2013/06/03 09:31 AM
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                                                  How'd you get this flower symbol as your user name ?Doug S Ꭳ❂〄☢⚓♜☎♬⚄☠2013/07/13 10:12 AM
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                                    Not reallyAnon2013/07/11 11:21 AM
                                    consistency, pleaseMichael S2013/07/11 11:22 AM
                                      consistency, pleaseLinus Torvalds2013/07/11 11:52 AM
                                        consistency, pleaseMichael S2013/07/11 02:43 PM
                                          consistency, pleaseLinus Torvalds2013/07/11 03:12 PM
                                            consistency, pleaseMark Roulo2013/07/11 03:54 PM
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                                                the discussion was about absence of AVX in SilvermontMark Roulo2013/07/11 04:19 PM
                                                  the discussion was about absence of AVX in SilvermontLinus Torvalds2013/07/12 09:16 AM
                                                    Thank youMark Roulo2013/07/12 09:58 AM
                                                    the discussion was about absence of AVX in Silvermontanon2013/07/12 10:10 AM
                                                      Not really (again)Anon2013/07/12 10:26 AM
                                                        Not really (again)anon2013/07/12 05:40 PM
                                                    the discussion was about absence of AVX in SilvermontLinus Torvalds2013/07/12 10:31 AM
                                                      you are wrong at about 100% of you saidMichael S2013/07/13 11:22 AM
                                                        you are wrong at about 100% of you saidLinus Torvalds2013/07/13 12:08 PM
                                                          you are wrong at about 100% of you saidMichael S2013/07/13 01:13 PM
                                                            you are wrong at about 100% of you saidLinus Torvalds2013/07/13 02:11 PM
                                                            you are wrong at about 100% of you saidvvid2013/07/13 03:20 PM
                                                              you are wrong at about 100% of you saidMichael S2013/07/14 01:38 AM
                                    Saltwell Outperforming A15...With Less Power!!!anon2013/07/11 06:41 PM
                                    Saltwell Outperforming A15...With Less Power!!!bakaneko2013/07/12 03:22 AM
                  Round 2: Baytrail benchmark (yes Antutu!) crushes Snapdragon 800.sammy2013/07/12 11:28 AM
                    Round 2: AnTuTu scores drop dramatically for AtomWilco2013/07/12 11:59 AM
                      Round 2: AnTuTu scores drop dramatically for AtomSteve2013/07/14 08:16 PM
                        Round 2: AnTuTu scores drop dramatically for AtomKlimax2013/07/14 10:59 PM
                        Round 2: AnTuTu scores drop dramatically for AtomDavid Kanter2013/07/15 01:57 PM
                          Intel is cheating AnTuTuWilco2013/07/15 03:43 PM
                            Intel is cheating AnTuTubakaneko2013/07/15 07:47 PM
                              Intel is cheating AnTuTuLinus Torvalds2013/07/15 08:45 PM
                                Intel is cheating AnTuTubakaneko2013/07/16 02:42 AM
                                  Intel is cheating AnTuTuWilco2013/07/16 03:47 AM
                                    Intel is cheating AnTuTubakaneko2013/07/16 05:50 AM
                                      Intel is cheating AnTuTuWilco2013/07/17 03:33 PM
                                        Intel is cheating AnTuTuKlimax2013/07/17 11:29 PM
                                          Intel is cheating AnTuTunone2013/07/17 11:35 PM
                                            Intel is cheating AnTuTuKlimax2013/07/18 01:41 AM
                                              Intel is cheating AnTuTuanon2013/07/18 02:10 AM
                                                Intel is cheating AnTuTuMichael S2013/07/18 03:39 AM
                                                Intel is cheating AnTuTuWilco2013/07/18 04:07 AM
                                                  Intel is cheating AnTuTunone2013/07/18 04:15 AM
                                                    Intel is cheating AnTuTuWilco2013/07/18 05:18 AM
                                                    Intel is cheating AnTuTuMichael S2013/07/18 06:44 AM
                                                      Intel is cheating AnTuTunone2013/07/18 07:47 AM
                                                        strict aliasingMichael S2013/07/18 08:10 AM
                                                          strict aliasing rules have existed since C89 (NT)Ricardo B2013/07/18 05:28 PM
                                                  Intel is cheating AnTuTuKlimax2013/07/18 11:30 AM
                                                Intel is cheating AnTuTuKlimax2013/07/18 11:39 AM
                                                  Intel is cheating AnTuTuanon2013/07/18 12:05 PM
                                                    Intel is cheating AnTuTuKlimax2013/07/20 12:05 AM
                                                      Intel is cheating AnTuTunone2013/07/20 02:50 AM
                                                  Intel is cheating AnTuTunone2013/07/18 12:38 PM
                                                    Intel is cheating AnTuTuKlimax2013/07/19 11:57 PM
                                  Intel is cheating AnTuTuLinus Torvalds2013/07/16 12:32 PM
                                Intel is cheating AnTuTu2013/07/16 03:16 AM
                                  Intel is cheating AnTuTubakaneko2013/07/16 04:55 AM
                                    Intel is cheating AnTuTuWilco2013/07/17 03:46 PM
                                      Intel is cheating AnTuTubakaneko2013/07/18 02:05 PM
                                      Intel is cheating AnTuTuDavid Kanter2013/07/19 02:31 AM
                          Round 2: AnTuTu scores drop dramatically for Atomanon2013/07/15 04:43 PM
                            Round 2: AnTuTu scores drop dramatically for Atomnone2013/07/16 12:15 AM
                          Round 2: AnTuTu scores drop dramatically for AtomGroo2013/07/16 07:35 AM
        ARM at Computexanon2013/06/04 10:43 PM
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