Instruction Scheduling?

Hi,


In Robert Blainey's paper on instruction scheduling for the RS6000 he looks
for instrunctions that are ready to schedle on a given cycle, and allocates
resources for them as he finds each ready instruction. If he finds another
ready instruction that needs the same resources that have already been
allocated to another instruction, he chooses between the two. If the
instruction that was given the resources turns out to have a lower priority
it gets evicted.


My question is instead of allocating resources to a ready instruction as soon
as it is found, why not collect all the ready instructions. Then sort them
by priority and allocate resources (for dispatch) in that order. This way
you avoid backtracking and the possibility of cycling.


What are the pros and cons of his approach versus the conventional way of
collecting and prioritizing all ready instructions before allocating resources?


Thanks,
Sanjoy Ghosh
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