[Haskell-cafe] Re: Parallel Pi
-Ursprüngliche Nachricht- Von: Simon Marlow marlo...@gmail.com Gesendet: 19.03.2010 09:24:12 An: Daniel Fischer daniel.is.fisc...@web.de Betreff: Re: Parallel Pi On 18/03/10 22:52, Daniel Fischer wrote: Am Donnerstag 18 März 2010 22:44:55 schrieb Simon Marlow: On 17/03/10 21:30, Daniel Fischer wrote: It works for me (GHC 6.12.1): SPARKS: 1 (1 converted, 0 pruned) INIT time0.00s ( 0.00s elapsed) MUT time9.05s ( 4.54s elapsed) GCtime0.12s ( 0.09s elapsed) EXIT time0.00s ( 0.01s elapsed) Total time9.12s ( 4.63s elapsed) wall-clock speedup of 1.93 on 2 cores. Is that Artyom's original code or with the pseq'ed length? Your fixed version. Good. So I can at least continue to believe I have a rough idea of how GHC behaves. And, with -N2, I also have a productivity of 193.5%, but the elapsed time is larger than the elapsed time for -N1. How long does it take with -N1 for you? The 1.93 speedup was compared to the time for -N1 (8.98s in my case). What hardware are you using there? 3.06GHz Pentium 4, 2 cores. I have mixed results with parallelism, some programmes get a speed-up of nearly a factor 2 (wall-clock time), others 1.4, 1.5 or so, yet others take about the same wall-clock time as the single threaded programme, some - like this - take longer despite using both cores intensively. I suspect it's something specific to that processor, probably cache-related. Perhaps we've managed to put some data frequently accessed by both CPUs on the same cache line. I'd have to do some detailed profiling on that processor to find out though. If you're have the time and inclination, install oprofile and look for things like memory ordering stalls. It seems that I've just been fooled by /proc/cpuinfo listing it as two and having something like 190% cpu usage in top/time. Being oblivious of almost everything hardware-related, I naively took it at face value. In fact it's probably just one hyperthreaded CPU, so since the two threads here do exactly the same type of work, it's natural then that it doesn't give a speed-up. Have you tried changing any GC settings? I've played around a little with -qg and -qb and -C, but that showed little influence. Any tips what else might be worth a try? -A would be the other thing to try. Cheers, Simon Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parallel Pi
On Mar 18, 2010, at 21:25 , Xiao-Yong Jin wrote: On Fri, 19 Mar 2010 01:22:58 +0100, Daniel Fischer wrote: core id : 0 cpu cores : 1 It is one of those pathetic single core pentium4 with so called hyper-threading enabled. You should have checked the intel product spreadsheet before investing such an old cpu. I'm a little surprised it's using both; I thought Linux (and other OSes) had disabled HTT by default because of the cache sniffing attacks. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parallel Pi
On Mar 18, 2010, at 21:58 , Daniel Fischer wrote: Am Freitag 19 März 2010 02:25:47 schrieb Xiao-Yong Jin: On Fri, 19 Mar 2010 01:22:58 +0100, Daniel Fischer wrote: core id : 0 cpu cores : 1 It is one of those pathetic single core pentium4 with so called hyper-threading enabled. 'kay, but why does it say processor : 0 ... processor : 1 ? Because that's how Linux presents what amounts to CPU resources, whether real (multiple cores) or virtual (HTT). You need to scan down to the core information to see if they're real or not. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parallel Pi
On 18/03/10 22:52, Daniel Fischer wrote: Am Donnerstag 18 März 2010 22:44:55 schrieb Simon Marlow: On 17/03/10 21:30, Daniel Fischer wrote: Am Mittwoch 17 März 2010 19:49:57 schrieb Artyom Kazak: Hello! I tried to implement the parallel Monte-Carlo method of computing Pi number, using two cores: move But it uses only on core: snip We see that our one spark is pruned. Why? Well, the problem is that your tasks don't do any real work - yet. piMonte returns a thunk pretty immediately, that thunk is then evaluated by show, long after your chance for parallelism is gone. You must force the work to be done _in_ r1 and r2, then you get parallelism: Generation 0: 2627 collections, 2626 parallel, 0.14s, 0.12s elapsed Generation 1: 1 collections, 1 parallel, 0.00s, 0.00s elapsed Parallel GC work balance: 1.79 (429262 / 240225, ideal 2) MUT time (elapsed) GC time (elapsed) Task 0 (worker) :0.00s( 8.22s) 0.00s( 0.00s) Task 1 (worker) :8.16s( 8.22s) 0.01s( 0.01s) Task 2 (worker) :8.00s( 8.22s) 0.13s( 0.11s) Task 3 (worker) :0.00s( 8.22s) 0.00s( 0.00s) SPARKS: 1 (1 converted, 0 pruned) INIT time0.00s ( 0.00s elapsed) MUT time 16.14s ( 8.22s elapsed) GCtime0.14s ( 0.12s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time 16.29s ( 8.34s elapsed) %GC time 0.9% (1.4% elapsed) Alloc rate163,684,377 bytes per MUT second Productivity 99.1% of total user, 193.5% of total elapsed But alas, it is slower than the single-threaded calculation :( INIT time0.00s ( 0.00s elapsed) MUT time7.08s ( 7.10s elapsed) GCtime0.08s ( 0.08s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time7.15s ( 7.18s elapsed) It works for me (GHC 6.12.1): SPARKS: 1 (1 converted, 0 pruned) INIT time0.00s ( 0.00s elapsed) MUT time9.05s ( 4.54s elapsed) GCtime0.12s ( 0.09s elapsed) EXIT time0.00s ( 0.01s elapsed) Total time9.12s ( 4.63s elapsed) wall-clock speedup of 1.93 on 2 cores. Is that Artyom's original code or with the pseq'ed length? Your fixed version. And, with -N2, I also have a productivity of 193.5%, but the elapsed time is larger than the elapsed time for -N1. How long does it take with -N1 for you? The 1.93 speedup was compared to the time for -N1 (8.98s in my case). What hardware are you using there? 3.06GHz Pentium 4, 2 cores. I have mixed results with parallelism, some programmes get a speed-up of nearly a factor 2 (wall-clock time), others 1.4, 1.5 or so, yet others take about the same wall-clock time as the single threaded programme, some - like this - take longer despite using both cores intensively. I suspect it's something specific to that processor, probably cache-related. Perhaps we've managed to put some data frequently accessed by both CPUs on the same cache line. I'd have to do some detailed profiling on that processor to find out though. If you're have the time and inclination, install oprofile and look for things like memory ordering stalls. Have you tried changing any GC settings? I've played around a little with -qg and -qb and -C, but that showed little influence. Any tips what else might be worth a try? -A would be the other thing to try. Cheers, Simon Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parallel Pi
Daniel Fischer daniel.is.fisc...@web.de writes:
3.06GHz Pentium 4, 2 cores.
[I.e. a single-core hyperthreaded CPU]
I have mixed results with parallelism, some programmes get a speed-up of
nearly a factor 2 (wall-clock time), others 1.4, 1.5 or so, yet others take
about the same wall-clock time as the single threaded programme, some -
like this - take longer despite using both cores intensively.
Given the negative press around HT, I'm surprised you see this good
results on many programs. I thought the main benefit from Intel's HT was
to reduce the impact of memory latency, that is, when one thread was
blocking on memory, it could switch immediately to anther, ready-to-run,
thread. (I may be misunderstanding this, though).
I think the general consensus was a 10-15% speedup from HT.
Anyway, the thing to get these days is of course Nehalem, A.K.A. Core
i{3,5,7}, which seems to give a nice speedup over Core 2. Among other
things, it dynamically overclocks the busy cores (using the
more market-friendly term turbo mode), making it even harder to
compare performance reliably. Interesting times.
-k
--
If I haven't seen further, it is by standing in the footprints of giants
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parallel Pi
On 19/03/10 09:00, Ketil Malde wrote: Daniel Fischerdaniel.is.fisc...@web.de writes: 3.06GHz Pentium 4, 2 cores. [I.e. a single-core hyperthreaded CPU] Ah, that would definitely explain a lack of parallelism. I'm just grateful we don't have another one of those multicore cache-line performance bugs, becuase they're a nightmare to track down. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parallel Pi
On 17/03/10 21:30, Daniel Fischer wrote: Am Mittwoch 17 März 2010 19:49:57 schrieb Artyom Kazak: Hello! I tried to implement the parallel Monte-Carlo method of computing Pi number, using two cores: move But it uses only on core: snip We see that our one spark is pruned. Why? Well, the problem is that your tasks don't do any real work - yet. piMonte returns a thunk pretty immediately, that thunk is then evaluated by show, long after your chance for parallelism is gone. You must force the work to be done _in_ r1 and r2, then you get parallelism: Generation 0: 2627 collections, 2626 parallel, 0.14s, 0.12s elapsed Generation 1: 1 collections, 1 parallel, 0.00s, 0.00s elapsed Parallel GC work balance: 1.79 (429262 / 240225, ideal 2) MUT time (elapsed) GC time (elapsed) Task 0 (worker) :0.00s( 8.22s) 0.00s( 0.00s) Task 1 (worker) :8.16s( 8.22s) 0.01s( 0.01s) Task 2 (worker) :8.00s( 8.22s) 0.13s( 0.11s) Task 3 (worker) :0.00s( 8.22s) 0.00s( 0.00s) SPARKS: 1 (1 converted, 0 pruned) INIT time0.00s ( 0.00s elapsed) MUT time 16.14s ( 8.22s elapsed) GCtime0.14s ( 0.12s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time 16.29s ( 8.34s elapsed) %GC time 0.9% (1.4% elapsed) Alloc rate163,684,377 bytes per MUT second Productivity 99.1% of total user, 193.5% of total elapsed But alas, it is slower than the single-threaded calculation :( INIT time0.00s ( 0.00s elapsed) MUT time7.08s ( 7.10s elapsed) GCtime0.08s ( 0.08s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time7.15s ( 7.18s elapsed) It works for me (GHC 6.12.1): SPARKS: 1 (1 converted, 0 pruned) INIT time0.00s ( 0.00s elapsed) MUT time9.05s ( 4.54s elapsed) GCtime0.12s ( 0.09s elapsed) EXIT time0.00s ( 0.01s elapsed) Total time9.12s ( 4.63s elapsed) wall-clock speedup of 1.93 on 2 cores. What hardware are you using there? Have you tried changing any GC settings? Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parallel Pi
Daniel Fischer wrote: 3.06GHz Pentium 4, 2 cores. Do you have more info on that? Try: grep 'model name' /proc/cpuinfo The original Pentium 4 (eg Intel(R) Pentium(R) 4 CPU 3.00GHz) had hyperthreading which was actually pretty pathetic for parallelism. The Core 2 Duos (eg Intel(R) Core(TM)2 Duo CPU T9600 @ 2.80GHz) are far superior. Erik -- -- Erik de Castro Lopo http://www.mega-nerd.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parallel Pi
Am Freitag 19 März 2010 00:56:15 schrieb Erik de Castro Lopo: Daniel Fischer wrote: 3.06GHz Pentium 4, 2 cores. Do you have more info on that? Try: grep 'model name' /proc/cpuinfo Well, $ cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 15 model : 4 model name : Intel(R) Pentium(R) 4 CPU 3.06GHz stepping: 9 cpu MHz : 3058.795 cache size : 1024 KB physical id : 0 siblings: 2 core id : 0 cpu cores : 1 apicid : 0 initial apicid : 0 fdiv_bug: no hlt_bug : no f00f_bug: no coma_bug: no fpu : yes fpu_exception : yes cpuid level : 5 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc pebs bts pni monitor ds_cpl tm2 cid cx16 xtpr lahf_lm bogomips: 6117.59 clflush size: 64 power management: processor : 1 vendor_id : GenuineIntel cpu family : 15 model : 4 model name : Intel(R) Pentium(R) 4 CPU 3.06GHz stepping: 9 cpu MHz : 3058.795 cache size : 1024 KB physical id : 0 siblings: 2 core id : 0 cpu cores : 1 apicid : 1 initial apicid : 1 fdiv_bug: no hlt_bug : no f00f_bug: no coma_bug: no fpu : yes fpu_exception : yes cpuid level : 5 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc pebs bts pni monitor ds_cpl tm2 cid cx16 xtpr lahf_lm bogomips: 6118.20 clflush size: 64 power management: Does that mean two CPUs, each with two siblings, or what is the correct interpretation? The original Pentium 4 (eg Intel(R) Pentium(R) 4 CPU 3.00GHz) had hyperthreading which was actually pretty pathetic for parallelism. The Core 2 Duos (eg Intel(R) Core(TM)2 Duo CPU T9600 @ 2.80GHz) are far superior. But probably also far more expensive :) I bought something cheap and was actually surprised when I discovered that it seemed to have two Cores/CPUs. Erik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parallel Pi
On Fri, 19 Mar 2010 01:22:58 +0100, Daniel Fischer wrote: core id : 0 cpu cores : 1 It is one of those pathetic single core pentium4 with so called hyper-threading enabled. You should have checked the intel product spreadsheet before investing such an old cpu. -- Jc/*__o/* X\ * (__ Y*/\ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parallel Pi
Am Freitag 19 März 2010 02:25:47 schrieb Xiao-Yong Jin: On Fri, 19 Mar 2010 01:22:58 +0100, Daniel Fischer wrote: core id : 0 cpu cores : 1 It is one of those pathetic single core pentium4 with so called hyper-threading enabled. 'kay, but why does it say processor : 0 ... processor : 1 ? You should have checked the intel product spreadsheet before investing such an old cpu. It was the cheapest box in town :) And it was less old when I bought it. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parallel Pi
Daniel Fischer wrote: Am Freitag 19 März 2010 02:25:47 schrieb Xiao-Yong Jin: It is one of those pathetic single core pentium4 with so called hyper-threading enabled. 'kay, but why does it say processor : 0 ... processor : 1 Hyperthreading is explained here: http://www.pcstats.com/articleview.cfm?articleID=1302 As explained, two hyperthreads is not euqivalent to to CPU cores because the two hyperthreads share resources while 2 discrete cores do not. As I remember it, the performance of the Pentium 4s with HT never met up to the promise and that line was swiftly replaced by the Core 2 Duo range of CPUs which we actually quite good. As a rough and ready test, I compiled Ben Lippmeier's DDC compiler on the following CPUS: a) Intel(R) Pentium(R) 4 CPU 3.00GHz (2Meg cache) b) Intel(R) Core(TM)2 Duo CPU T9600 @ 2.80GHz (6Meg cache) Using the ghc-6.12.1 on both (32bit Ubuntu 10.04 chroot for the P4 and a 32bit Debian unstable chroot for the Core2Duo), compiling DDC took (using 'make clean ; time make'): a) 2m54.301s on the P4 HT b) 0m59.277s on the Core2Duo If nothing else, it shows that two CPUs with similar clock speeds and the same number of processors listed in /proc/cpuinfo can have vastly different performance characteristics. Erik -- -- Erik de Castro Lopo http://www.mega-nerd.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parallel Pi
Am Freitag 19 März 2010 04:24:21 schrieb Erik de Castro Lopo: Daniel Fischer wrote: Am Freitag 19 März 2010 02:25:47 schrieb Xiao-Yong Jin: It is one of those pathetic single core pentium4 with so called hyper-threading enabled. 'kay, but why does it say processor : 0 ... processor : 1 Hyperthreading is explained here: http://www.pcstats.com/articleview.cfm?articleID=1302 Thanks. That clears things up a little. Erik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
