On Tue, 20 Mar 2012 23:11:30 +0000, Graham Harris wrote: >... could be polluting all your processor caches a lot >more than you were experiencing previously on 3 CPs, which could lead to >increased overheads in the OS managing higher levels of cache-misses under >the covers.
The operating system does not get involved in cache misses. When the processor references storage that is not in the most local cache, the hardware retrieves it from the next level cache, if it is available there. If not, it tries the next level and the next. A z196 has a 4 level cache. IIRC a z10 has 3 levels of cache. If it can't be found in any cache, main storage is referenced. This all done entirely by the hardware, and it results in the instruction requiring more time to execute. To look at it another way, cache exists because main storage is very slow compared to the processor speed. Without cache, the processor would not be able to execute instructions nearly as fast as it could. Cache allows data from main storage to be kept very close to the processor in extremely fast memory, allowing the processor to execute instructions as fast as possible. -- Tom Marchant ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
