150 GFLOP/s measured?

Article: PhysX87: Software Deficiency
By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), July 19, 2010 11:56 am
Room: Moderated Discussions
hobold (hobold@vectorizer.org) on 7/19/10 wrote:
---------------------------
>Linus Torvalds (torvalds@linux-foundation.org) on 7/19/10 wrote:
>---------------------------
>[...]
>>- the kind of code you talk about is such a small fraction
>>of the code any real CPU runs that it's not really worth
>>even bringing up as an argument.
>
>This is a judgement call, not an objective fact.

Sure. That said, I've written some code like that myself.

And the thing is, the simple cases, OoO really does not
lose any performance. You can hand-tune the assembly, and
an OoO machine will run it quite well, probably very close
to optimally.

The annoying case is when you have unreliable OoO. The
only such case I've personally worked with is the P4: the
performance profile is almost random, and small changes
can result in ridiculous performance anomalies that are
not at all obvious.

So I would almost agree with Ian if the choice was
between in-order and the P4 style OoO. But that's not so
much about OoO as about the fact that the P4 just did some
really odd things with store buffer replay microtraps etc.

And yes, there are always specific loads where any kind
of speculation bites you. Again, it's not so much OoO vs
in-order: even with in-order you'd want things like branch
prediction etc, and under very specific loads that will do
the wrong thing, and you may curse the CPU for being "too
clever".

But there really are very few cases where you have both
highly tuned code and don't care about more than
one single version of the microarchitecture. And are willing
to forego all compilers (maybe you have a "smart assembler",
that's been done several times).

Linus
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        150 GFLOP/s measured?anon2010/07/08 07:10 PM
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            150 GFLOP/s measured?Aaron Spink2010/07/08 09:05 PM
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                                150 GFLOP/s measured?jrl2010/07/20 01:18 AM
                            150 GFLOP/s measured?anonymous422010/07/25 12:00 PM
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                                    150 GFLOP/s measured?anon2010/07/23 04:55 PM
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                                        150 GFLOP/s measured?anon2010/07/24 02:36 AM
                                    150 GFLOP/s measured?Vincent Diepeveen2010/07/27 05:37 PM
                                      150 GFLOP/s measured??2010/07/27 11:42 PM
                                        150 GFLOP/s measured?slacker2010/07/28 05:55 AM
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                            Separate the OoO-ness from speculative-nessMatt Sayler2010/07/20 06:10 PM
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                                          Separate the OoO-ness from speculative-nessanon2010/07/22 04:27 AM
                                      Separate the OoO-ness from speculative-nessslacker2010/07/21 07:45 PM
                                        Separate the OoO-ness from speculative-nessanon2010/07/22 01:57 AM
                                        Separate the OoO-ness from speculative-ness?2010/07/22 05:26 AM
                                          Separate the OoO-ness from speculative-nessDan Downs2010/07/22 08:14 AM
                                          Confusing and not very useful definitionDavid Kanter2010/07/22 12:41 PM
                                            Confusing and not very useful definition?2010/07/22 10:58 PM
                                              Confusing and not very useful definitionUngo2010/07/24 12:06 PM
                                                Confusing and not very useful definition?2010/07/25 10:23 PM
                            Separate the OoO-ness from speculative-nesssomeone2010/07/20 08:02 PM
                              Separate the OoO-ness from speculative-nessThiago Kurovski2010/07/21 04:13 PM
            You are just quoting SINGLE precision flops? OMG what planet do you live? Vincent Diepeveen2010/07/19 10:26 AM
              The prior poster was talking about SP (NT)David Kanter2010/07/19 11:34 AM
                All FFT's need double precisionVincent Diepeveen2010/07/19 02:02 PM
                  All FFT's need double precisionDavid Kanter2010/07/19 02:09 PM
                    All FFT's need double precisionVincent Diepeveen2010/07/19 04:06 PM
                  All FFT's need double precision - notMichael S2010/07/20 01:16 AM
                    All FFT's need double precision - notUngo2010/07/21 12:04 AM
                      All FFT's need double precision - notMichael S2010/07/21 02:35 PM
                      All FFT's need double precision - notEduardoS2010/07/21 02:52 PM
                        All FFT's need double precision - notAnon2010/07/21 05:23 PM
                          All FFT's need double precision - notRicardo B2010/07/26 07:46 AM
                        I'm on a boat!anon2010/07/22 11:42 AM
                        All FFT's need double precision - notVincent Diepeveen2010/07/24 11:39 PM
                          All FFT's need double precision - notslacker2010/07/25 03:27 AM
                            All FFT's need double precision - notRicardo B2010/07/26 07:40 AM
                          All FFT's need double precision - notEduardoS2010/07/25 08:37 AM
                            All FFT's need double precision - notMichael S2010/07/25 10:43 AM
                    All FFT's need double precision - notVincent Diepeveen2010/07/24 11:19 PM
      A bit off baseEduardoS2010/07/08 04:08 PM
        A bit off baseGroo2010/07/08 06:11 PM
          A bit off basejohn mann2010/07/08 06:58 PM
            All right...let's cool it...David Kanter2010/07/08 07:54 PM
    A bit off baseVincent Diepeveen2010/07/19 03:36 PM
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