
6.5 Case Studies: SGI Challenge and Sun Enterprise 6000 415
processor to the bus (the request queues pointing downward in Figure 6.10), so that
the multiple outstanding requests can be buffered and the processor or cache does
not stall. It may also be useful to have deeper response queues and more write-back
and other types of buffers, since the system now affords more concurrency As long
as deadlock is handled by separating requests from replies and providing them with
logically separate buffers, the exact length of any of these queues is not critical for
correctness. The reason for so few changes is that the lockup-free caches themselves ...