[C400-L] RE: Porting C Linux to ILE C: Performance problem

["Mike Mills" <mikem@xxxxxxxx>]

Zvi,

How much memory are you allocating?  In particular, are you allocating and
using more than 16MB?  It used to be that you could not malloc() more than
16MB of contiguous memory on the AS/400.  That limitation was removed a few
OS releases ago.  However, in the tests that I ran immediately after the
limitation was removed, I noticed that any access to memory over the 16MB
"barrier" was *very* slow.  I haven't tried this test in more recent
versions of the OS, but if it hasn't been "fixed", then perhaps this is your
problem - but only if you're using more than 16MB of memory.

You can test this yourself by writing a small C program that allocates, say,
32MB of memory, and then loops through 'touching' each byte.  If you print a
message every megabyte or so, you can see the slowdown immediately after
crossing the 16MB boundary - assuming the problem still exists.

If this does turn out to be your problem, one workaround is abstract out
your memory access such that you can maintain an _array_ of memory segments,
each one no more than 16MB in size.

FYI.

--
Mike Mills
mikem@xxxxxxxx
ConsulTech Information Systems, Inc.


> message: 1
> date: Wed, 30 Jun 2004 07:29:10 -0700 (PDT)
> from: Zvi Kave <zvi_kave@xxxxxxxxx>
> subject: [C400-L] Porting C Linux to ILE C: Performance problem
> 
> Dear collegues,
> 
> 1. I ported succesfully(?) C coded software from Linux
> 
>    to ILE C. 
> 2. The sample program I use, takes in Linux 1 second.
>    The same program run takes on the AS/400 ...
>    7 minutes!?
> 3. When debugging the program on the AS/400, I found
>    that the slow response is in the memory allocation
>    routines, namely, calloc, malloc, realloc and 
>    free().
>    CPU usage is about 10%.
> 4. Those memory management routines are managed by
>    linked list which is allocated in the beginning of
>    program and free()d before end.
> 
>  Is there any reason for that performance problem?
> 
>   Please help.
> 
>   Regards,
> 
>    Zvi   
> 
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