What is the CPU time for one paging in, and for one paging out?
Do you have any suggestion to measure CPU time or logical caluculation
formula for the CPU time would be also appreciated.
ANSWER
The following is from class notes on the SMP machines. It was to
illustrate the importance of a cache hit. These numbers were for
machines running from 75 - 150MHz.
Memory type Latency
L1 cache 0 - 1 cycles
L2 cache 5 - 10 cycles
Memory 20 - 50 cycles
Disk 750K - 1.5M cycles
As you can see these are big numbers. But, what this means is that
if a processor cannot do anything until data is retrieved from the
disk then it will wait about 750K cycles. Of course in a multi-
process environment like AIX the processor may run other tasks
during this time so the system could be in use.
Again, these were for the SPM machines and these numbers will be
specific to the different models.
ANSWER
R: Unfortunatly, the exact numbers you are looking for are not
available, but, I did find numbers more specific to the POWER2
chip.
The POWER2 chip has a very good memory subsystem. It takes
6 cycles to get data from L2 cache and 8 cycles form memory.
So, all of the penalty of getting data from disk, in page
space or from opening a file is from disk access. To
calculate the number of cycles to get the data back from
disk would involve many varaibles, such as seek time, if
the disk is currently busy with a different access, and
transfer rate of the disk. So, the numbers above are general
estimates for the time to access data on disk.
Thank You.
S e a r c h - k e y w o r d s:
PAGING PENALTY.
WWQA: ITEM: RTA000086522 ITEM: RTA000086522
Dated: 03/1995 Category: ITSAI6000GE
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