Report generated for the foo program

Hostname:  aixhost1.austin.ibm.com
Real memory size:   16.00 Mb
Time of day:  Thu Mar 18 19:04:04 2004
Command:  foo

Simulated memory size initialized to  16.00 Mb.

Number of iterations per memory size = 1 warm-up + 1 measured = 2.

Memory size  Avg. Pageins  Avg. Response Time    Avg. Pagein Rate
(megabytes)                     (sec.)           (pageins / sec.)
-----------------------------------------------------------------
16.00            115.0           123.9                 0.9
15.00            112.0           125.1                 0.9
14.00            179.0           126.2                 1.4
13.00             81.0           125.7                 0.6
12.00            403.0           132.0                 3.1
11.00            855.0           141.5                 6.0
10.00           1161.0           146.8                 7.9
9.00            1529.0           161.3                 9.5
8.00            2931.0           202.5                 14.5

The report consists of four columns. The leftmost column gives the memory size, while the Avg. Pageins column gives the average number of page-ins that occurred when the application was run at that memory size. It is important to note that the Avg. Pageins column refers to all page-in operations, including code, data, and file reads, from all programs, that completed while the application ran. The Avg. Response Time column gives the average amount of time it took the application to complete, while the Avg. Pagein Rate column gives the average rate of page-ins.

Concentrate on the Avg. Pagein Rate column. From 16 MB to 13 MB, the page-in rate is relatively small (< 1.5 page-ins per second). However, from 13 MB to 8 MB, the page-in rate grows gradually at first, and then rapidly as 8 MB is reached. The Avg. Response Time column has a similar shape: relatively flat at first, then increasing gradually, and finally increasing rapidly as the memory size is decreased to 8 MB.

Here, the page-in rate actually decreases when the memory size changes from 14 MB (1.4 page-ins per second) to 13 MB (0.6 page-ins per second). This is not cause for alarm. In an actual system, it is impossible to expect the results to be perfectly smooth. The important point is that the page-in rate is relatively low at both 14 MB and 13 MB.

Finally, you can make a couple of deductions from the report. First, if the performance of the application is deemed unacceptable at 8 MB (as it probably would be), then adding memory would enhance performance significantly. Note that the response time rises from approximately 124 seconds at 16 MB to 202 seconds at 8 MB, an increase of 63 percent. On the other hand, if the performance is deemed unacceptable at 16 MB, adding memory will not enhance performance much, because page-ins do not slow the program appreciably at 16 MB.