Article: PhysX87: Software Deficiency
By: anon (anon.delete@this.anon.com), July 21, 2010 5:53 pm
Room: Moderated Discussions
? (0xe2.0x9a.0x9b@gmail.com) on 7/21/10 wrote:
---------------------------
>anon (anon@anon.com) on 7/21/10 wrote:
>---------------------------
>>But you're wrong about this as an example of how pipelining requires speculation
>>because CPUs disallow such sequences without cache and pipeline draining instructions.
>
>There are two options of how to design a pipelined version of a CPU:
>
>1. Maintain full compatibility between the pipelined and non-pipelined versions,
>even for all the unlikely corner-cases such as intense self-modifying code. The
>two CPUs give mathematically identical results in all possible cases.
>
>2. Do not maintain full compatibility. One specimen of this approach are the transitions
>from 8086 to 286 to 386 to 486 etc.
>
>I was mainly talking about case (1).
snip
>>Exceptions are another one, but again it could have imprecise exceptions and not require speculative execution.
>
>Well, but you cannot go back to 1970 and fix 8086 so that it knows about the concept of imprecise exceptions.
>
snip
>>On the contrary, I think your assertion that pipelining requires speculative execution is wrong.
>
>I am not saying that. I am saying this: Pipelining, the way it is implemented in
>current CPUs (e.g: Core2), involves certain assumptions
I'm sorry, but you're just modifying your argument as you go along now. You can't tell me you were talking specifically about x86 and constraints of market realities in CPU design. Because we can all read what you posted to Linus.
"NOTE that this theoretical OoO CPU I am mentioning here
is *not* doing any *speculation* (except maybe those
which also present in the in-order CPU). Once you have
speculation, there by necessity exist some cases in which
the CPU's prediction engine will make a wrong decision.
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 !!!"
You are clearliy talking about theoretical designs, and you were saying that pipelining requires speculation.
snip
>>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?
>
>(Note: I am *not* against caches)
>
Yes there is a speculative nature about caches, of course it is nothing to do with speculative execution or anything in the CPU pipeline which is what this discussion was supposed to be about (out of order versus in order, pipelining, speculative execution etc). I'll quote you again
"Even mere pipelining entails a small dose of speculative
execution !!!"
I'm not saying you don't know the difference, but I'm saying that the argument about execution engines is only muddied by you bringing up caches.
---------------------------
>anon (anon@anon.com) on 7/21/10 wrote:
>---------------------------
>>But you're wrong about this as an example of how pipelining requires speculation
>>because CPUs disallow such sequences without cache and pipeline draining instructions.
>
>There are two options of how to design a pipelined version of a CPU:
>
>1. Maintain full compatibility between the pipelined and non-pipelined versions,
>even for all the unlikely corner-cases such as intense self-modifying code. The
>two CPUs give mathematically identical results in all possible cases.
>
>2. Do not maintain full compatibility. One specimen of this approach are the transitions
>from 8086 to 286 to 386 to 486 etc.
>
>I was mainly talking about case (1).
snip
>>Exceptions are another one, but again it could have imprecise exceptions and not require speculative execution.
>
>Well, but you cannot go back to 1970 and fix 8086 so that it knows about the concept of imprecise exceptions.
>
snip
>>On the contrary, I think your assertion that pipelining requires speculative execution is wrong.
>
>I am not saying that. I am saying this: Pipelining, the way it is implemented in
>current CPUs (e.g: Core2), involves certain assumptions
I'm sorry, but you're just modifying your argument as you go along now. You can't tell me you were talking specifically about x86 and constraints of market realities in CPU design. Because we can all read what you posted to Linus.
"NOTE that this theoretical OoO CPU I am mentioning here
is *not* doing any *speculation* (except maybe those
which also present in the in-order CPU). Once you have
speculation, there by necessity exist some cases in which
the CPU's prediction engine will make a wrong decision.
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 !!!"
You are clearliy talking about theoretical designs, and you were saying that pipelining requires speculation.
snip
>>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?
>
>(Note: I am *not* against caches)
>
Yes there is a speculative nature about caches, of course it is nothing to do with speculative execution or anything in the CPU pipeline which is what this discussion was supposed to be about (out of order versus in order, pipelining, speculative execution etc). I'll quote you again
"Even mere pipelining entails a small dose of speculative
execution !!!"
I'm not saying you don't know the difference, but I'm saying that the argument about execution engines is only muddied by you bringing up caches.
Topic | Posted By | Date |
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A bit off base | John Mann | 2010/07/07 07:04 AM |
A bit off base | David Kanter | 2010/07/07 11:28 AM |
SSE vs x87 | Joel Hruska | 2010/07/07 12:53 PM |
SSE vs x87 | Michael S | 2010/07/07 01:07 PM |
SSE vs x87 | hobold | 2010/07/08 05:12 AM |
SSE vs x87 | David Kanter | 2010/07/07 02:55 PM |
SSE vs x87 | Andi Kleen | 2010/07/08 02:43 AM |
80 bit FP | Ricardo B | 2010/07/08 07:35 AM |
80 bit FP | David Kanter | 2010/07/08 11:14 AM |
80 bit FP | Kevin G | 2010/07/08 02:12 PM |
80 bit FP | Ian Ollmann | 2010/07/19 12:49 AM |
80 bit FP | David Kanter | 2010/07/19 11:33 AM |
80 bit FP | Anil Maliyekkel | 2010/07/19 04:49 PM |
80 bit FP | rwessel | 2010/07/19 05:41 PM |
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80 bit FP | Emil Briggs | 2010/07/22 09:06 AM |
A bit off base | John Mann | 2010/07/08 11:06 AM |
A bit off base | David Kanter | 2010/07/08 11:27 AM |
A bit off base | Ian Ameline | 2010/07/09 10:10 AM |
A bit off base | Michael S | 2010/07/10 02:13 PM |
A bit off base | Ian Ameline | 2010/07/11 07:51 AM |
A bit off base | David Kanter | 2010/07/07 09:46 PM |
A bit off base | Anon | 2010/07/08 12:47 AM |
A bit off base | anon | 2010/07/08 02:15 AM |
A bit off base | Gabriele Svelto | 2010/07/08 04:11 AM |
Physics engine history | Peter Clare | 2010/07/08 04:49 AM |
Physics engine history | Null Pointer Exception | 2010/07/08 06:07 AM |
Physics engine history | Ralf | 2010/07/08 03:09 PM |
Physics engine history | David Kanter | 2010/07/08 04:16 PM |
Physics engine history | sJ | 2010/07/08 11:36 PM |
Physics engine history | Gabriele Svelto | 2010/07/09 12:59 AM |
Physics engine history | sJ | 2010/07/13 06:35 AM |
Physics engine history | David Kanter | 2010/07/09 09:25 AM |
Physics engine history | sJ | 2010/07/13 06:49 AM |
Physics engine history | fvdbergh | 2010/07/13 07:27 AM |
A bit off base | John Mann | 2010/07/08 11:11 AM |
A bit off base | David Kanter | 2010/07/08 11:31 AM |
150 GFLOP/s measured? | anon | 2010/07/08 07:10 PM |
150 GFLOP/s measured? | David Kanter | 2010/07/08 07:53 PM |
150 GFLOP/s measured? | Aaron Spink | 2010/07/08 09:05 PM |
150 GFLOP/s measured? | anon | 2010/07/08 09:31 PM |
150 GFLOP/s measured? | Aaron Spink | 2010/07/08 10:43 PM |
150 GFLOP/s measured? | David Kanter | 2010/07/08 11:27 PM |
150 GFLOP/s measured? | Ian Ollmann | 2010/07/19 01:14 AM |
150 GFLOP/s measured? | anon | 2010/07/19 06:39 AM |
150 GFLOP/s measured? | hobold | 2010/07/19 07:26 AM |
Philosophy for achieving peak | David Kanter | 2010/07/19 11:49 AM |
150 GFLOP/s measured? | Linus Torvalds | 2010/07/19 07:36 AM |
150 GFLOP/s measured? | Richard Cownie | 2010/07/19 08:42 AM |
150 GFLOP/s measured? | Aaron Spink | 2010/07/19 08:56 AM |
150 GFLOP/s measured? | hobold | 2010/07/19 09:30 AM |
150 GFLOP/s measured? | Groo | 2010/07/19 02:31 PM |
150 GFLOP/s measured? | hobold | 2010/07/19 04:17 PM |
150 GFLOP/s measured? | Groo | 2010/07/19 06:18 PM |
150 GFLOP/s measured? | Anon | 2010/07/19 06:18 PM |
150 GFLOP/s measured? | Mark Roulo | 2010/07/19 11:47 AM |
150 GFLOP/s measured? | slacker | 2010/07/19 12:55 PM |
150 GFLOP/s measured? | Mark Roulo | 2010/07/19 01:00 PM |
150 GFLOP/s measured? | anonymous42 | 2010/07/25 12:31 PM |
150 GFLOP/s measured? | Richard Cownie | 2010/07/19 12:41 PM |
150 GFLOP/s measured? | Linus Torvalds | 2010/07/19 02:57 PM |
150 GFLOP/s measured? | Richard Cownie | 2010/07/19 04:10 PM |
150 GFLOP/s measured? | Richard Cownie | 2010/07/19 04:10 PM |
150 GFLOP/s measured? | hobold | 2010/07/19 04:25 PM |
150 GFLOP/s measured? | Linus Torvalds | 2010/07/19 04:31 PM |
150 GFLOP/s measured? | Richard Cownie | 2010/07/20 06:04 AM |
150 GFLOP/s measured? | jrl | 2010/07/20 01:18 AM |
150 GFLOP/s measured? | anonymous42 | 2010/07/25 12:00 PM |
150 GFLOP/s measured? | David Kanter | 2010/07/25 12:52 PM |
150 GFLOP/s measured? | Anon | 2010/07/19 06:15 PM |
150 GFLOP/s measured? | Linus Torvalds | 2010/07/19 07:27 PM |
150 GFLOP/s measured? | Anon | 2010/07/19 09:54 PM |
150 GFLOP/s measured? | anon | 2010/07/19 11:45 PM |
150 GFLOP/s measured? | hobold | 2010/07/19 09:14 AM |
150 GFLOP/s measured? | Linus Torvalds | 2010/07/19 11:56 AM |
150 GFLOP/s measured? | a reader | 2010/07/21 08:16 PM |
150 GFLOP/s measured? | Linus Torvalds | 2010/07/21 09:05 PM |
150 GFLOP/s measured? | anon | 2010/07/22 02:09 AM |
150 GFLOP/s measured? | a reader | 2010/07/22 07:53 PM |
150 GFLOP/s measured? | gallier2 | 2010/07/23 05:58 AM |
150 GFLOP/s measured? | a reader | 2010/07/25 08:35 AM |
150 GFLOP/s measured? | David Kanter | 2010/07/25 11:49 AM |
150 GFLOP/s measured? | a reader | 2010/07/26 07:03 PM |
150 GFLOP/s measured? | Michael S | 2010/07/28 01:38 AM |
150 GFLOP/s measured? | Gabriele Svelto | 2010/07/28 01:44 AM |
150 GFLOP/s measured? | anon | 2010/07/23 04:55 PM |
150 GFLOP/s measured? | slacker | 2010/07/24 12:48 AM |
150 GFLOP/s measured? | anon | 2010/07/24 02:36 AM |
150 GFLOP/s measured? | Vincent Diepeveen | 2010/07/27 05:37 PM |
150 GFLOP/s measured? | ? | 2010/07/27 11:42 PM |
150 GFLOP/s measured? | slacker | 2010/07/28 05:55 AM |
Intel's clock rate projections | AM | 2010/07/28 02:03 AM |
nostalgia ain't what it used to be | someone | 2010/07/28 05:38 AM |
Intel's clock rate projections | AM | 2010/07/28 10:12 PM |
Separate the OoO-ness from speculative-ness | ? | 2010/07/20 07:19 AM |
Separate the OoO-ness from speculative-ness | Mark Christiansen | 2010/07/20 02:26 PM |
Separate the OoO-ness from speculative-ness | slacker | 2010/07/20 06:04 PM |
Separate the OoO-ness from speculative-ness | Matt Sayler | 2010/07/20 06:10 PM |
Separate the OoO-ness from speculative-ness | slacker | 2010/07/20 09:37 PM |
Separate the OoO-ness from speculative-ness | ? | 2010/07/20 11:51 PM |
Separate the OoO-ness from speculative-ness | anon | 2010/07/21 02:16 AM |
Separate the OoO-ness from speculative-ness | ? | 2010/07/21 07:05 AM |
Software conventions | Paul A. Clayton | 2010/07/21 08:52 AM |
Software conventions | ? | 2010/07/22 05:43 AM |
Speculation | David Kanter | 2010/07/21 10:32 AM |
Pipelining affects the ISA | ? | 2010/07/22 10:58 PM |
Pipelining affects the ISA | ? | 2010/07/22 11:14 PM |
Pipelining affects the ISA | rwessel | 2010/07/23 12:03 AM |
Pipelining affects the ISA | ? | 2010/07/23 05:50 AM |
Pipelining affects the ISA | ? | 2010/07/23 06:10 AM |
Pipelining affects the ISA | Thiago Kurovski | 2010/07/23 02:59 PM |
Pipelining affects the ISA | anon | 2010/07/24 07:35 AM |
Pipelining affects the ISA | Thiago Kurovski | 2010/07/24 11:12 AM |
Pipelining affects the ISA | Gabriele Svelto | 2010/07/26 02:50 AM |
Pipelining affects the ISA | IlleglWpns | 2010/07/26 05:14 AM |
Pipelining affects the ISA | Michael S | 2010/07/26 03:33 PM |
Separate the OoO-ness from speculative-ness | anon | 2010/07/21 05:53 PM |
Separate the OoO-ness from speculative-ness | ? | 2010/07/22 04:15 AM |
Separate the OoO-ness from speculative-ness | anon | 2010/07/22 04:27 AM |
Separate the OoO-ness from speculative-ness | slacker | 2010/07/21 07:45 PM |
Separate the OoO-ness from speculative-ness | anon | 2010/07/22 01:57 AM |
Separate the OoO-ness from speculative-ness | ? | 2010/07/22 05:26 AM |
Separate the OoO-ness from speculative-ness | Dan Downs | 2010/07/22 08:14 AM |
Confusing and not very useful definition | David Kanter | 2010/07/22 12:41 PM |
Confusing and not very useful definition | ? | 2010/07/22 10:58 PM |
Confusing and not very useful definition | Ungo | 2010/07/24 12:06 PM |
Confusing and not very useful definition | ? | 2010/07/25 10:23 PM |
Separate the OoO-ness from speculative-ness | someone | 2010/07/20 08:02 PM |
Separate the OoO-ness from speculative-ness | Thiago Kurovski | 2010/07/21 04:13 PM |
You are just quoting SINGLE precision flops? OMG what planet do you live? | Vincent Diepeveen | 2010/07/19 10:26 AM |
The prior poster was talking about SP (NT) | David Kanter | 2010/07/19 11:34 AM |
All FFT's need double precision | Vincent Diepeveen | 2010/07/19 02:02 PM |
All FFT's need double precision | David Kanter | 2010/07/19 02:09 PM |
All FFT's need double precision | Vincent Diepeveen | 2010/07/19 04:06 PM |
All FFT's need double precision - not | Michael S | 2010/07/20 01:16 AM |
All FFT's need double precision - not | Ungo | 2010/07/21 12:04 AM |
All FFT's need double precision - not | Michael S | 2010/07/21 02:35 PM |
All FFT's need double precision - not | EduardoS | 2010/07/21 02:52 PM |
All FFT's need double precision - not | Anon | 2010/07/21 05:23 PM |
All FFT's need double precision - not | Ricardo B | 2010/07/26 07:46 AM |
I'm on a boat! | anon | 2010/07/22 11:42 AM |
All FFT's need double precision - not | Vincent Diepeveen | 2010/07/24 11:39 PM |
All FFT's need double precision - not | slacker | 2010/07/25 03:27 AM |
All FFT's need double precision - not | Ricardo B | 2010/07/26 07:40 AM |
All FFT's need double precision - not | EduardoS | 2010/07/25 08:37 AM |
All FFT's need double precision - not | Michael S | 2010/07/25 10:43 AM |
All FFT's need double precision - not | Vincent Diepeveen | 2010/07/24 11:19 PM |
A bit off base | EduardoS | 2010/07/08 04:08 PM |
A bit off base | Groo | 2010/07/08 06:11 PM |
A bit off base | john mann | 2010/07/08 06:58 PM |
All right...let's cool it... | David Kanter | 2010/07/08 07:54 PM |
A bit off base | Vincent Diepeveen | 2010/07/19 03:36 PM |