levy@nsc.nsc.com (Jonathan Levy) (01/14/89)
I am cross posting this from the 68k group to the 32k group for interest. In article <216@unet.UUCP> jimmc@unet.PacBell.COM (Jim McCrae) writes: > > Also, has anyone noticed that the instruction cache on the > 68030 can actually slow down execution speed? We saw this > during evaluation and as yet have no explanation. Yes, this can happen. Small caches, with low hit ratios can increase the bus load due to line fills in burst mode. The situation becomes worse if wait states are evident. The increased bus load then can interfere with other bus activity that the processor needs to perform ( such as operand reads or writes). You may try to disable burst mode and verify this. (The above information is theoretical, and is based on analysis that we had done when selecting cache size for the NS32532. The Instruction cache was selected to be 512 bytes, as smaller caches had this danger of actually degrading performance) Jonathan