more cache manager issues

[Joel Sherrill]

Eric Norum wrote:
> 
> Till Straumann wrote:
> 
> > An alternative to this approach would be letting
> > rtems_cache_aligned_malloc()
> > using its own heap with a bigger (cache aligned) granularity.
> 
> Yes, but now there's another configuration parameter to be dealt with.
> Deciding on where to split the heaps adds more of a burden to the
> application programmer.
> 
> >
> > One global `free(arg)' function could then determine the heap
> > corresponding to the argument
> > by comparing the argument pointer to the standard heap / aligned heap
> > starting and end addresses.
> >
> > Even more elegant would of course be an object oriented approach with a
> > virtual `free' member
> > function (or a field in the block header holding the information about
> > which version of `free' must
> > be used for that specific block of memory).
> 
> Yep.  Maybe the memory allocation routines (both regular and cache
> aligned) should be rewritten to do this.

FYI the way the heap code is designed the minimum block size is 4 bytes
or 1 unsigned32 and allocations are always multiples of 4.  If you look 
closely you will see the least significant bit of the front/back flags
is used as an indicator of used/free.  It is possible that the next
bit could indicate cache aligned allocation or not.  I don't know if
this
helps or not.

ALso -- there is NOTHING preventing the entire replacement of the 
libc/malloc code.  There is nothing sacred about the use of a
region.  It was just convenient.  The region is implemented to the
RTEID/ORKID specification, there is almost certainly a better
malloc implementation for embedded systems.

> >
> > IMHO, the need to call a `special' deallocator function is very error
> > prone.
> 
> Agreed.
> My quick solution to the problem wasn't very good.
> 
> I'm not yet convinced that dual heaps is a good idea, though.
> 
> --
> Eric Norum                                 eric at cls.usask.ca
> Canadian Light Source                      Phone: (306) 966-6308
> University of Saskatchewan                 FAX:   (306) 966-6058
> Saskatoon, Canada.

-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel at OARcorp.com                 On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
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