By the way, I understand that the current PDL uses the total number of
processors as a default for set_autopthread_targ. Is this a good
default? The documentation says that the gain after 4 pthreads is not
much, and using more could be counterproductive. For example:
No threads:
$ perl -MTime::HiRes=time -MPDL -E '
set_autopthread_targ(shift) if @ARGV; $x = zeroes(5000,5000);
$y =5; $t=time; $z=$x+$y; say "Time: ", time-$t, "\nThreads: ",
get_autopthread_actual();
' 0
Time: 0.0815010070800781
Threads: 0
Two threads:
$ perl -MTime::HiRes=time -MPDL -E '
set_autopthread_targ(shift) if @ARGV; $x = zeroes(5000,5000);
$y =5; $t=time; $z=$x+$y; say "Time: ", time-$t, "\nThreads: ",
get_autopthread_actual();
' 2
Time: 0.0741269588470459
Threads: 2
There is a gain, but small.
Four threads:
mochan@tlahuilli:~$ perl -MTime::HiRes=time -MPDL -E '
set_autopthread_targ(shift) if @ARGV; $x = zeroes(5000,5000);
$y =5; $t=time; $z=$x+$y; say "Time: ", time-$t, "\nThreads: ",
get_autopthread_actual();
' 4
Time: 0.0751421451568604
Threads: 4
Slightly worse.
Default:
mochan@tlahuilli:~$ perl -MTime::HiRes=time -MPDL -E '
set_autopthread_targ(shift) if @ARGV; $x = zeroes(5000,5000);
$y =5; $t=time; $z=$x+$y; say "Time: ", time-$t, "\nThreads: ",
get_autopthread_actual();
'
Time: 0.0870430469512939
Threads: 48
Even worse with 48 threads.
Maybe this is a bad example to show the benefits of pthreads. Is there
a simple more convincing case?
Regards,
Luis
--
o
W. Luis Mochán, | tel:(52)(777)329-1734 /<(*)
Instituto de Ciencias Físicas, UNAM | fax:(52)(777)317-5388 `>/ /\
Av. Universidad s/n CP 62210 | (*)/\/ \
Cuernavaca, Morelos, México | [email protected] /\_/\__/
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