Separate the OoO-ness from speculative-ness

Article: PhysX87: Software Deficiency
By: slacker (s.delete@this.lack.er), July 21, 2010 6:45 pm
Room: Moderated Discussions
? (0xe2.0x9a.0x9b@gmail.com) on 7/21/10 wrote:
---------------------------
>anon (anon@anon.com) on 7/21/10 wrote:
>---------------------------
>>On the contrary, I think your assertion that pipelining requires speculative execution is wrong.
>
>I am not saying that. I am saying this:....

"Even mere pipelining entails a small dose of speculative execution !!!

I will repeat it one more time, because it seems to me that you are
completely missing this: Even mere pipelining entails a small dose of
speculation !!!"

How foolish of us to confuse your words with your intentions!


>Code: Hi there, CPU, my friend. I want you to execute me.
>
>CPU: No problem. Hand me the first couple of your instructions.
>
>Code: Only a couple of them? You mean you don't want to see all of them?
>
>CPU: That's right.
>
>Code: But but, then, you aren't going to know what I am going to do.
>
>CPU: Don't worry. I will manage.
>
>Code: How?

I knew this was the problem; you are playing loose and fast with your terminology.


>>Caches have nothing to do with speculative execution that you were talking about.
>
>What are you saying? That if a contemporary CPU (Core2 or whatever) decides to
>allocate a cache-line for data at address 0x1230, it is not making any speculations
>about future uses of that piece of data?

You are expanding and abusing the term "speculative execution," which is both pointless and inane. It has a narrow definition in hardware circles; speculative execution is the execution of code which has not yet been determined by the program stream to be necessary.

- Prefetching code and data is not speculative execution
- Decoding instructions in to microops is not speculative execution
- Caching data is not speculative execution

But if we're going to be silly about terminology, then let's go crazy:

- A microprocessor speculates that its circuits have not failed after each clock cycle

- A microprocessor speculates that it is being supplied with sufficient electric potential to power the circuits properly

- Virtually all software speculates that the instruction semantics on a processor adhere to some specification (ISA) without actually confirming the semantics.
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                                          Separate the OoO-ness from speculative-nessanon2010/07/22 03:27 AM
                                      Separate the OoO-ness from speculative-nessslacker2010/07/21 06:45 PM
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                                        Separate the OoO-ness from speculative-ness?2010/07/22 04:26 AM
                                          Separate the OoO-ness from speculative-nessDan Downs2010/07/22 07:14 AM
                                          Confusing and not very useful definitionDavid Kanter2010/07/22 11:41 AM
                                            Confusing and not very useful definition?2010/07/22 09:58 PM
                                              Confusing and not very useful definitionUngo2010/07/24 11:06 AM
                                                Confusing and not very useful definition?2010/07/25 09:23 PM
                            Separate the OoO-ness from speculative-nesssomeone2010/07/20 07:02 PM
                              Separate the OoO-ness from speculative-nessThiago Kurovski2010/07/21 03:13 PM
            You are just quoting SINGLE precision flops? OMG what planet do you live? Vincent Diepeveen2010/07/19 09:26 AM
              The prior poster was talking about SP (NT)David Kanter2010/07/19 10:34 AM
                All FFT's need double precisionVincent Diepeveen2010/07/19 01:02 PM
                  All FFT's need double precisionDavid Kanter2010/07/19 01:09 PM
                    All FFT's need double precisionVincent Diepeveen2010/07/19 03:06 PM
                  All FFT's need double precision - notMichael S2010/07/20 12:16 AM
                    All FFT's need double precision - notUngo2010/07/20 11:04 PM
                      All FFT's need double precision - notMichael S2010/07/21 01:35 PM
                      All FFT's need double precision - notEduardoS2010/07/21 01:52 PM
                        All FFT's need double precision - notAnon2010/07/21 04:23 PM
                          All FFT's need double precision - notRicardo B2010/07/26 06:46 AM
                        I'm on a boat!anon2010/07/22 10:42 AM
                        All FFT's need double precision - notVincent Diepeveen2010/07/24 10:39 PM
                          All FFT's need double precision - notslacker2010/07/25 02:27 AM
                            All FFT's need double precision - notRicardo B2010/07/26 06:40 AM
                          All FFT's need double precision - notEduardoS2010/07/25 07:37 AM
                            All FFT's need double precision - notMichael S2010/07/25 09:43 AM
                    All FFT's need double precision - notVincent Diepeveen2010/07/24 10:19 PM
      A bit off baseEduardoS2010/07/08 03:08 PM
        A bit off baseGroo2010/07/08 05:11 PM
          A bit off basejohn mann2010/07/08 05:58 PM
            All right...let's cool it...David Kanter2010/07/08 06:54 PM
    A bit off baseVincent Diepeveen2010/07/19 02:36 PM
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