Article: ARM Goes 64-bit
By: David Kanter (dkanter.delete@this.realworldtech.com), November 21, 2012 10:12 am
Room: Moderated Discussions
Wilco (Wilco.Dijkstra.delete@this.ntlworld.com) on November 21, 2012 6:41 am wrote:
> David Kanter (dkanter.delete@this.realworldtech.com) on November 20, 2012 11:07 pm wrote:
> > Rohit (a.delete@this.b.c) on November 20, 2012 4:48 pm wrote:
> > > David Kanter (dkanter.delete@this.realworldtech.com) on November 19, 2012 3:40 pm wrote:
> > > > That's probably a common view. However, there are a number of optimizations that can net
> > > > you huge performance gains and are only viable for JIT systems. I agree you want to do
> > > > as much as possible in your compiler, but somethings require dynamic information.
> > > >
> > > > DK
> > >
> > > Which optimizations are these?
> >
> > Speculative multi-threading using a JIT.
>
> That's not at all JIT related. Has anyone ever shown a speedup using software-only speculation?
Yes, albeit only small ones.
> Automatic multihreading ARMs have been studied for many years. However even with special hardware
> support to detect conflicts, fast rollbacks and spawning threads to different cores it never
> seemed worth the relatively small speedups, especially not when you consider the extra power
> for speculating. The big speedups were all in loops which can be dealt with normally.
Apparently they were studied poorly. I can tell you from my own experience that ARM really has minimal interest in this area and has explored it far less than other CPU companies.
You don't really pay extra power for speculating. If you compare two well-designed systems; one can run the same software on 2 threads and one on 4 threads...there's going to be quite a performance gap. So as long as your speculative overhead isn't 50%, you're probably OK.
Mis-speculation can consume quite a bit of power, but that just means you have to be careful.
> To repeat, I don't believe there are any optimizations which are much better done in a JIT than in
> a static compiler. Even dynamic info like profiling works better when done the >traditional way.
You're welcome to believe that, but you'd be wrong. I've seen plenty of data to the contrary.
Moreover, there's plenty of public data from TMTA about optimizations which are only possible through JITing.
DK
> David Kanter (dkanter.delete@this.realworldtech.com) on November 20, 2012 11:07 pm wrote:
> > Rohit (a.delete@this.b.c) on November 20, 2012 4:48 pm wrote:
> > > David Kanter (dkanter.delete@this.realworldtech.com) on November 19, 2012 3:40 pm wrote:
> > > > That's probably a common view. However, there are a number of optimizations that can net
> > > > you huge performance gains and are only viable for JIT systems. I agree you want to do
> > > > as much as possible in your compiler, but somethings require dynamic information.
> > > >
> > > > DK
> > >
> > > Which optimizations are these?
> >
> > Speculative multi-threading using a JIT.
>
> That's not at all JIT related. Has anyone ever shown a speedup using software-only speculation?
Yes, albeit only small ones.
> Automatic multihreading ARMs have been studied for many years. However even with special hardware
> support to detect conflicts, fast rollbacks and spawning threads to different cores it never
> seemed worth the relatively small speedups, especially not when you consider the extra power
> for speculating. The big speedups were all in loops which can be dealt with normally.
Apparently they were studied poorly. I can tell you from my own experience that ARM really has minimal interest in this area and has explored it far less than other CPU companies.
You don't really pay extra power for speculating. If you compare two well-designed systems; one can run the same software on 2 threads and one on 4 threads...there's going to be quite a performance gap. So as long as your speculative overhead isn't 50%, you're probably OK.
Mis-speculation can consume quite a bit of power, but that just means you have to be careful.
> To repeat, I don't believe there are any optimizations which are much better done in a JIT than in
> a static compiler. Even dynamic info like profiling works better when done the >traditional way.
You're welcome to believe that, but you'd be wrong. I've seen plenty of data to the contrary.
Moreover, there's plenty of public data from TMTA about optimizations which are only possible through JITing.
DK
Topic | Posted By | Date |
---|---|---|
New Article: ARM Goes 64-bit | David Kanter | 2012/08/14 12:04 AM |
New Article: ARM Goes 64-bit | none | 2012/08/14 12:44 AM |
New Article: ARM Goes 64-bit | David Kanter | 2012/08/14 01:04 AM |
MIPS MT-ASE | Paul A. Clayton | 2012/08/14 09:01 AM |
MONITOR/MWAIT | EduardoS | 2012/08/14 10:08 AM |
MWAIT not specifically MT | Paul A. Clayton | 2012/08/14 10:36 AM |
MWAIT not specifically MT | EduardoS | 2012/08/15 03:16 PM |
MONITOR/MWAIT | anonymou5 | 2012/08/14 11:07 AM |
MONITOR/MWAIT | EduardoS | 2012/08/15 03:20 PM |
MIPS MT-ASE | rwessel | 2012/08/14 10:14 AM |
New Article: ARM Goes 64-bit | SHK | 2012/08/14 02:01 AM |
New Article: ARM Goes 64-bit | anon | 2012/08/14 02:37 AM |
New Article: ARM Goes 64-bit | Richard Cownie | 2012/08/14 03:57 AM |
New Article: ARM Goes 64-bit | anon | 2012/08/14 04:29 AM |
New Article: ARM Goes 64-bit | none | 2012/08/14 04:44 AM |
New Article: ARM Goes 64-bit | anon | 2012/08/14 05:28 AM |
New Article: ARM Goes 64-bit | anon | 2012/08/14 05:32 AM |
New Article: ARM Goes 64-bit | EduardoS | 2012/08/14 06:06 AM |
New Article: ARM Goes 64-bit | none | 2012/08/14 05:40 AM |
AArch64 select better than cmov | Paul A. Clayton | 2012/08/14 06:08 AM |
New Article: ARM Goes 64-bit | anon | 2012/08/14 06:12 AM |
New Article: ARM Goes 64-bit | none | 2012/08/14 06:25 AM |
Predicated ld/store are useful | Paul A. Clayton | 2012/08/14 06:48 AM |
Predicated ld/store are useful | none | 2012/08/14 06:56 AM |
Predicated ld/store are useful | anon | 2012/08/14 07:07 AM |
Predicated stores might not be that bad | Paul A. Clayton | 2012/08/14 07:27 AM |
Predicated stores might not be that bad | David Kanter | 2012/08/15 01:14 AM |
Predicated stores might not be that bad | Michael S | 2012/08/15 11:41 AM |
Predicated stores might not be that bad | R Byron | 2012/08/17 04:09 AM |
New Article: ARM Goes 64-bit | anon | 2012/08/14 06:54 AM |
New Article: ARM Goes 64-bit | none | 2012/08/14 07:04 AM |
New Article: ARM Goes 64-bit | anon | 2012/08/14 07:43 AM |
New Article: ARM Goes 64-bit | EduardoS | 2012/08/14 06:07 AM |
New Article: ARM Goes 64-bit | anon | 2012/08/14 06:20 AM |
New Article: ARM Goes 64-bit | none | 2012/08/14 06:29 AM |
New Article: ARM Goes 64-bit | anon | 2012/08/14 07:00 AM |
New Article: ARM Goes 64-bit | Michael S | 2012/08/14 03:43 PM |
New Article: ARM Goes 64-bit | Richard Cownie | 2012/08/14 06:53 AM |
OT: Conrad's "Youth" | Richard Cownie | 2012/08/14 07:20 AM |
New Article: ARM Goes 64-bit | EduardoS | 2012/08/14 06:04 AM |
New Article: ARM Goes 64-bit | mpx | 2012/08/14 08:59 AM |
New Article: ARM Goes 64-bit | Antti-Ville Tuunainen | 2012/08/14 09:16 AM |
New Article: ARM Goes 64-bit | anonymou5 | 2012/08/14 11:03 AM |
New Article: ARM Goes 64-bit | name99 | 2012/11/17 03:31 PM |
Microarchitecting a counter register | Paul A. Clayton | 2012/11/17 07:37 PM |
New Article: ARM Goes 64-bit | bakaneko | 2012/08/14 04:21 AM |
New Article: ARM Goes 64-bit | name99 | 2012/11/17 03:40 PM |
New Article: ARM Goes 64-bit | EduardoS | 2012/11/17 04:52 PM |
New Article: ARM Goes 64-bit | Doug S | 2012/11/17 05:48 PM |
New Article: ARM Goes 64-bit | bakaneko | 2012/11/18 05:40 PM |
New Article: ARM Goes 64-bit | Wilco | 2012/11/19 07:59 AM |
New Article: ARM Goes 64-bit | EduardoS | 2012/11/19 08:23 AM |
New Article: ARM Goes 64-bit | Wilco | 2012/11/19 09:31 AM |
Downloading µarch-specific binaries? | Paul A. Clayton | 2012/11/19 11:21 AM |
New Article: ARM Goes 64-bit | EduardoS | 2012/11/19 11:41 AM |
New Article: ARM Goes 64-bit | Wilco | 2012/11/21 07:44 AM |
JIT vs. static compilation (Was: New Article: ARM Goes 64-bit) | VMguy | 2012/11/22 03:21 AM |
JIT vs. static compilation (Was: New Article: ARM Goes 64-bit) | David Kanter | 2012/11/22 12:12 PM |
JIT vs. static compilation (Was: New Article: ARM Goes 64-bit) | Gabriele Svelto | 2012/11/23 03:50 AM |
New Article: ARM Goes 64-bit | EduardoS | 2012/11/23 10:09 AM |
New Article: ARM Goes 64-bit | EBFE | 2012/11/26 01:24 AM |
New Article: ARM Goes 64-bit | Gabriele Svelto | 2012/11/26 03:33 AM |
New Article: ARM Goes 64-bit | EBFE | 2012/11/27 11:17 PM |
New Article: ARM Goes 64-bit | Gabriele Svelto | 2012/11/28 02:32 AM |
New Article: ARM Goes 64-bit | EduardoS | 2012/11/26 12:16 PM |
New Article: ARM Goes 64-bit | EBFE | 2012/11/28 12:33 AM |
New Article: ARM Goes 64-bit | EduardoS | 2012/11/28 05:53 AM |
New Article: ARM Goes 64-bit | Michael S | 2012/11/28 06:15 AM |
New Article: ARM Goes 64-bit | EduardoS | 2012/11/28 07:33 AM |
New Article: ARM Goes 64-bit | Michael S | 2012/11/28 09:16 AM |
New Article: ARM Goes 64-bit | EduardoS | 2012/11/28 09:53 AM |
New Article: ARM Goes 64-bit | Eugene Nalimov | 2012/11/28 05:58 PM |
Amazing! | EduardoS | 2012/11/28 07:25 PM |
Amazing! (non-italic response) | EduardoS | 2012/11/28 07:25 PM |
Amazing! | EBFE | 2012/11/28 08:20 PM |
Undefined behaviour doubles down | EduardoS | 2012/11/28 09:10 PM |
New Article: ARM Goes 64-bit | EBFE | 2012/11/28 07:54 PM |
New Article: ARM Goes 64-bit | EduardoS | 2012/11/28 09:21 PM |
Have you heard of Transmeta? | David Kanter | 2012/11/19 03:47 PM |
New Article: ARM Goes 64-bit | bakaneko | 2012/11/19 09:08 AM |
New Article: ARM Goes 64-bit | David Kanter | 2012/11/19 03:40 PM |
Semantic Dictionary Encoding | Ray | 2012/11/19 10:37 PM |
New Article: ARM Goes 64-bit | Rohit | 2012/11/20 04:48 PM |
New Article: ARM Goes 64-bit | David Kanter | 2012/11/20 11:07 PM |
New Article: ARM Goes 64-bit | Wilco | 2012/11/21 06:41 AM |
New Article: ARM Goes 64-bit | David Kanter | 2012/11/21 10:12 AM |
A JIT example | Mark Roulo | 2012/11/21 10:30 AM |
A JIT example | Wilco | 2012/11/21 07:04 PM |
A JIT example | rwessel | 2012/11/21 09:05 PM |
A JIT example | Gabriele Svelto | 2012/11/23 03:53 AM |
A JIT example | EduardoS | 2012/11/23 10:13 AM |
A JIT example | Wilco | 2012/11/23 01:41 PM |
A JIT example | EduardoS | 2012/11/23 02:06 PM |
A JIT example | Gabriele Svelto | 2012/11/23 04:09 PM |
A JIT example | Symmetry | 2012/11/26 05:58 AM |
New Article: ARM Goes 64-bit | Ray | 2012/11/19 10:27 PM |
New Article: ARM Goes 64-bit | David Kanter | 2012/08/14 09:11 AM |
v7-M is Thumb-only | Paul A. Clayton | 2012/08/14 06:58 AM |
Minor suggested correction | Paul A. Clayton | 2012/08/14 08:33 AM |
Minor suggested correction | anon | 2012/08/14 08:57 AM |
New Article: ARM Goes 64-bit | Exophase | 2012/08/14 08:33 AM |
New Article: ARM Goes 64-bit | David Kanter | 2012/08/14 09:16 AM |
New Article: ARM Goes 64-bit | jigal | 2012/08/15 01:49 PM |
Correction re ARM and BBC Micro | Paul | 2012/08/14 08:59 PM |
Correction re ARM and BBC Micro | Per Hesselgren | 2012/08/15 03:27 AM |
Memory BW so low | Per Hesselgren | 2012/08/15 03:14 AM |
Memory BW so low | none | 2012/08/15 11:16 AM |
New Article: ARM Goes 64-bit | dado | 2012/08/15 10:25 AM |
Number of GPRs | Kenneth Jonsson | 2012/08/16 02:35 PM |
Number of GPRs | Exophase | 2012/08/16 02:52 PM |
Number of GPRs | Kenneth Jonsson | 2012/08/17 02:41 AM |
Ooops, missing link... | Kenneth Jonsson | 2012/08/17 02:44 AM |
64-bit pointers eat some performance | Paul A. Clayton | 2012/08/17 06:19 AM |
64-bit pointers eat some performance | bakaneko | 2012/08/17 08:37 AM |
Brute force seems to work | Paul A. Clayton | 2012/08/17 10:08 AM |
Brute force seems to work | bakaneko | 2012/08/17 11:15 AM |
64-bit pointers eat some performance | Richard Cownie | 2012/08/17 08:46 AM |
Pointer compression is atypical | Paul A. Clayton | 2012/08/17 10:43 AM |
Pointer compression is atypical | Richard Cownie | 2012/08/17 12:57 PM |
Pointer compression is atypical | Howard Chu | 2012/08/22 10:17 PM |
Pointer compression is atypical | Richard Cownie | 2012/08/23 04:48 AM |
Pointer compression is atypical | Howard Chu | 2012/08/23 06:51 AM |
Pointer compression is atypical | Wilco | 2012/08/17 02:41 PM |
Pointer compression is atypical | Richard Cownie | 2012/08/17 04:13 PM |
Pointer compression is atypical | Ricardo B | 2012/08/19 10:44 AM |
Pointer compression is atypical | Howard Chu | 2012/08/22 10:08 PM |
Unified libraries? | Paul A. Clayton | 2012/08/23 07:49 AM |
Pointer compression is atypical | Richard Cownie | 2012/08/23 08:44 AM |
Pointer compression is atypical | Howard Chu | 2012/08/23 05:17 PM |
Pointer compression is atypical | anon | 2012/08/23 08:15 PM |
Pointer compression is atypical | Howard Chu | 2012/08/23 09:33 PM |
64-bit pointers eat some performance | Foo_ | 2012/08/18 12:09 PM |
64-bit pointers eat some performance | Richard Cownie | 2012/08/18 05:25 PM |
64-bit pointers eat some performance | Richard Cownie | 2012/08/18 05:32 PM |
Page-related benefit of small pointers | Paul A. Clayton | 2012/08/23 08:36 AM |
Number of GPRs | Wilco | 2012/08/17 06:31 AM |
Number of GPRs | Kenneth Jonsson | 2012/08/17 11:54 AM |
Number of GPRs | Exophase | 2012/08/17 12:44 PM |
Number of GPRs | Kenneth Jonsson | 2012/08/17 01:22 PM |
Number of GPRs | Wilco | 2012/08/17 02:53 PM |
What about dynamic utilization? | Exophase | 2012/08/17 09:30 AM |
Compiler vs. assembly aliasing knowledge? | Paul A. Clayton | 2012/08/17 10:20 AM |
Compiler vs. assembly aliasing knowledge? | Exophase | 2012/08/17 11:09 AM |
Compiler vs. assembly aliasing knowledge? | anon | 2012/08/18 02:23 AM |
Compiler vs. assembly aliasing knowledge? | Ricardo B | 2012/08/19 11:02 AM |
Compiler vs. assembly aliasing knowledge? | anon | 2012/08/19 06:07 PM |
Compiler vs. assembly aliasing knowledge? | Ricardo B | 2012/08/19 07:26 PM |
Compiler vs. assembly aliasing knowledge? | anon | 2012/08/19 10:03 PM |
Compiler vs. assembly aliasing knowledge? | anon | 2012/08/20 01:59 AM |
Number of GPRs | David Kanter | 2012/08/17 12:46 PM |
RAT issues as part of reason 1 | Paul A. Clayton | 2012/08/17 02:18 PM |
Number of GPRs | name99 | 2012/11/17 06:37 PM |
Large ARFs increase renaming cost | Paul A. Clayton | 2012/11/17 09:23 PM |
Number of GPRs | David Kanter | 2012/08/16 03:31 PM |
Number of GPRs | Richard Cownie | 2012/08/16 05:17 PM |
32 GPRs ~2-3% | Paul A. Clayton | 2012/08/16 06:27 PM |
Oops, Message-ID: aaed6e38-c7bd-467e-ba41-f40cf1020e5e@googlegroups.com (NT) | Paul A. Clayton | 2012/08/16 06:29 PM |
32 GPRs ~2-3% | Exophase | 2012/08/16 10:06 PM |
R31 as SP/zero is kind of neat (NT) | Paul A. Clayton | 2012/08/17 06:23 AM |
32 GPRs ~2-3% | rwessel | 2012/08/17 08:24 AM |
32 GPRs ~2-3% | Exophase | 2012/08/17 09:16 AM |
32 GPRs ~2-3% | Max | 2012/08/17 04:19 PM |
32 GPRs ~2-3% | name99 | 2012/11/17 07:43 PM |
Number of GPRs | mpx | 2012/08/17 01:11 AM |
Latency and power | Paul A. Clayton | 2012/08/17 06:54 AM |
Number of GPRs | bakaneko | 2012/08/17 03:09 AM |
New Article: ARM Goes 64-bit | Steve | 2012/08/17 02:12 PM |
New Article: ARM Goes 64-bit | David Kanter | 2012/08/19 12:42 PM |
New Article: ARM Goes 64-bit | Doug S | 2012/08/19 02:02 PM |
New Article: ARM Goes 64-bit | Anon | 2012/08/19 07:16 PM |
New Article: ARM Goes 64-bit | Steve | 2012/08/30 07:51 AM |
Scalar vs Vector registers | Robert David Graham | 2012/08/19 05:19 PM |
Scalar vs Vector registers | David Kanter | 2012/08/19 05:29 PM |
New Article: ARM Goes 64-bit | Baserock ARM servers | 2012/08/21 04:13 PM |
Baserock ARM servers | Sysanon | 2012/08/21 04:14 PM |
A-15 virtualization and LPAE? | Paul A. Clayton | 2012/08/21 06:13 PM |
A-15 virtualization and LPAE? | Anon | 2012/08/21 07:13 PM |
Half-depth advantages? | Paul A. Clayton | 2012/08/21 08:42 PM |
Half-depth advantages? | Anon | 2012/08/22 03:33 PM |
Thanks for the information (NT) | Paul A. Clayton | 2012/08/22 04:04 PM |
A-15 virtualization and LPAE? | C. Ladisch | 2012/08/23 11:12 AM |
A-15 virtualization and LPAE? | Paul | 2012/08/23 03:17 PM |
Excessive pessimism | Paul A. Clayton | 2012/08/23 04:08 PM |
Excessive pessimism | David Kanter | 2012/08/23 05:05 PM |
New Article: ARM Goes 64-bit | Michael S | 2012/08/22 07:12 AM |
BTW, Baserock==product, Codethink==company (NT) | Paul A. Clayton | 2012/08/22 08:56 AM |
New Article: ARM Goes 64-bit | Reinoud Zandijk | 2012/08/21 11:27 PM |
New Article: ARM Goes 64-bit | Robert Pearson | 2021/07/26 09:11 AM |
New Article: ARM Goes 64-bit | anon | 2021/07/26 11:03 AM |
New Article: ARM Goes 64-bit | none | 2021/07/26 11:45 PM |
New Article: ARM Goes 64-bit | dmcq | 2021/07/27 07:36 AM |
New Article: ARM Goes 64-bit | Chester | 2021/07/27 01:21 PM |
New Article: ARM Goes 64-bit | none | 2021/07/27 10:37 PM |
New Article: ARM Goes 64-bit | anon | 2021/07/26 11:04 AM |