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Re: Slow array indexing [message #29214 is a reply to message #29204]

Wed, 06 February 2002 09:26

Nigel Wade
Messages: 286
Registered: March 1998

Senior Member

trouble wrote:

> Hi,
>
> Another array query - accessing arrays seems very slow in 5.5 (Alpha
> Linux)
>
> IDL> array = INTARR(256,256,10)
> IDL> iz = [0,2,4,6,8]
> IDL> t=systime(1)&new = array[*,*,iz]&print,systime(1)-t
> 11.529402
>

Is it really taking that much time or is it miscalculating systime()?

>
> Compare this with 5.4 (Alpha OSF unix) on a slower machine:
> 0.039039969
>
>

That's about what I get with IRIX, Solaris and Linux/x86.

> Anyone know what's going on here ?

Not a clue. Something strange in Alpha Linux.

What happens if you run strace on idl? E.g. put the commands in a file
(script.pro) and run

strace idl script.pro

If the IDL executable is similar for Alpha as it is for x86 there should be
two calls to gettimeofday (one each for the calls to systime()). Is
anything strange going on in between them (all I get is two calls to mmap2
and one call to munmap, presumably allocating/releasing storage for the
arrays created).?

--
-----------------------------------------------------------
Nigel Wade, System Administrator, Space Plasma Physics Group,
University of Leicester, Leicester, LE1 7RH, UK
E-mail : nmw@ion.le.ac.uk
Phone : +44 (0)116 2523568, Fax : +44 (0)116 2523555

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[Message index]

		Re: Slow array indexing By: Nigel Wade on Thu, 07 February 2002 10:09
		Re: Slow array indexing By: the_cacc on Thu, 07 February 2002 09:17
		Re: Slow array indexing By: the_cacc on Thu, 07 February 2002 02:21
		Re: Slow array indexing By: Nigel Wade on Thu, 07 February 2002 01:45
		Re: Slow array indexing By: Nigel Wade on Wed, 06 February 2002 09:26
		Re: Slow array indexing By: the_cacc on Wed, 06 February 2002 09:15

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