Prefmem of bus 3
Eric W. Biederman
ebiederman at lnxi.com
Tue Mar 9 17:59:01 CET 2004
Li-Ta Lo <ollie at lanl.gov> writes:
> On Mon, 2004-03-01 at 14:06, Eric W. Biederman wrote:
> > There are many was to assign resources on a bus. After some
> > experiences with tight memory situations I implemented a near optimal
> > solution. The solution is optimal if all of your resources are a
> > power of 2 in size.
> > Basically the code is a loop. For each iteration the
> > code finds the largest unassigned resource. Then the resource
> > constraints of that resource are considered and padding between
> > the previous resources and the current resources are inserted if
> > necessary. Then we get into the next iteration.
> I still don't understand this. Do you mean that now the resource
> allocation is not sequential (in the order of devices been enumerated)
> and not continuous (there are gaps in allocated address) ?
The reason the allocation is not sequential (in the order of devices
been enumerated) is to reduce the number of gaps in the allocated
So a thought problem to help put this in perspective.
First all resources are a power of 2 in size must be that same
power of 2 aligned.
So if I have 3 resources A,B,C with the following sizes:
Allocating them sequentially would use 756M of address space.
After allocating A you need nearly 256M of padding to get B 256M
aligned. C takes nearly 256M due to padding.
Allocating them largest to smallest (B,A,C) uses just 512M of address
space. Because the alignment necessary for A is present at the end
of B, and the alignment necessary for A is present at the end of C.
> > The reason this is optimal if all of your resources are a power of
> > two in size is because if your previous resource is a larger or equal
> > power of two no padding will be needed for the current resource.
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