Article: PhysX87: Software Deficiency
By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), July 19, 2010 2:57 pm
Room: Moderated Discussions
Richard Cownie (tich@pobox.com) on 7/19/10 wrote:
>
>Sure. But it's a trade-off of silicon and power.
But that's only a valid argument if you are in a situation
where you don't have enough power and silicon to do OoO.
The thing I objected to was that Ian was essentially
arguing against OoO given that he had it. That means
that there is not any question about whether you have
the transistors or the power envelope to do OoO. So he
wasn't talking about some milliwatt part that did in-order
because it couldn't afford to do OoO.
He was saying that given OoO, he finds it a hindrance to
his performance work. Which is claim is basically always
total bullsh*t. Yes, OoO is often harder to analyze, the
same way caches make things harder to analyze, but that's
because it's more complicated. The code runs faster, and
in-order would make the problem of optimizing simpler, but
the end result would be slower.
Performance is tough. To get best performance, you need
to do complicated things. You need to accept the fact that
you need caching, you need out-of-order, and you tend to
often need fairly complex data structures with indexing,
locking and other fancy features.
Complaining about the fact that things get complex is
kind of pointless. Simplicity wouldn't get you to the
point you are aiming for.
(Of course, sometimes the answer is to make things
simpler, but that's because you made a mess of things, and
you need to start from the beginning. Complexity is not a
a-priori sign of high performance - but high performance
often does require complexity).
Linus
>
>Sure. But it's a trade-off of silicon and power.
But that's only a valid argument if you are in a situation
where you don't have enough power and silicon to do OoO.
The thing I objected to was that Ian was essentially
arguing against OoO given that he had it. That means
that there is not any question about whether you have
the transistors or the power envelope to do OoO. So he
wasn't talking about some milliwatt part that did in-order
because it couldn't afford to do OoO.
He was saying that given OoO, he finds it a hindrance to
his performance work. Which is claim is basically always
total bullsh*t. Yes, OoO is often harder to analyze, the
same way caches make things harder to analyze, but that's
because it's more complicated. The code runs faster, and
in-order would make the problem of optimizing simpler, but
the end result would be slower.
Performance is tough. To get best performance, you need
to do complicated things. You need to accept the fact that
you need caching, you need out-of-order, and you tend to
often need fairly complex data structures with indexing,
locking and other fancy features.
Complaining about the fact that things get complex is
kind of pointless. Simplicity wouldn't get you to the
point you are aiming for.
(Of course, sometimes the answer is to make things
simpler, but that's because you made a mess of things, and
you need to start from the beginning. Complexity is not a
a-priori sign of high performance - but high performance
often does require complexity).
Linus
Topic | Posted By | Date |
---|---|---|
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 |
80 bit FP | Matt Waldhauer | 2010/07/21 11:11 AM |
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 |