[Haskell-cafe] Re: Parallel Pi

[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

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
-- 
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Erik de Castro Lopo
http://www.mega-nerd.com/