S/390 PartnerWorld for Developers, ITSO/EFS Project EFS Systems on a Linux Base: Additional Topics

Chapter 2. Tuning considerations 23

product. The instruction cache requires an average of 11 bytes for each S/390 instruction byte

cached. A S/390 LA instruction, for example, requires 44 bytes in the cache.

You can monitor the effectiveness of the instruction cache with the d cachestats command:

flexes> d cachestats

Cache hits: 20465153/212253141 96%

Cache misses: 760188/212253141 4% <== monitor this number

...

The number of cache misses in this report is the critical information. If this number is above

about 4 percent, you should increase your cachesize parameter. (But never increase it to the

point where Linux starts paging!) If the number is considerably less than 4 percent, you

might make better use of your server memory by increasing the defined S/390 memory size,

defining more S/390 expanded memory, or increasing disk cache sizes. The CLI command

clear cachestats will reset the statistics. The counters overflow, and you will probably need

to reset the statistics before monitoring them.

FSI has not documented the meanings of the other statistics in this report.

Prior to FLEX-ES Release 6.2.12, the d cachestats command, by default, displays

information for processor zero. If you have more than one processor enabled for S/390

emulation and want to display statistics for more than processor zero, you need to first issue a

set cpu command:

flexes> set cpu 0 1 (display information for two processors)

flexes> d cachestats

The set cpu command

The CLI command set cpu, used in the previous example, affects more than the display of

cache statistics. It affects most of the CLI commands that could be directed to multiple

emulated S/390 CPUs (when they exist). For example, if you have a FLEX-ES instance with

three emulated S/390 CPUs and enter:

flexes> set cpu 2

flexes> ipl A80 0A92CS

then emulated S/390 CPU number 2 would be IPLed instead of the default CPU number zero.

For z/OS this makes no practical difference. For z/VM, the IPLed CPU is used as the

Master

Processor

.

If you want to display the general registers in CPU 0 and 1, you could:

flexes> set cpu 0 1

flexes> d g

If you want to see the registers only in CPU 1, you could set cpu 1 and issue the appropriate

display command.

2.7 Memory tuning

There are several ways you can tune FLEX-ES. Adding more processors, or faster

processors, or more memory, or faster disks, or other hardware changes can be considered a

form of tuning. Within a given hardware system (with a fixed number of processors licensed