Chapter 8. Performance and scalability considerations 137
PAZXXQ04 105 11 93 130 149 393K 303K .0 75K 100 1536M VMS,DSC,DISP
PAZXXD01 77 17 60 1210 284 249K 249K .0 212K 100 1536M VMS,DSC,DISP
<--- DEVICE ---> <----- DEVICE RDEV DATA ------> <-- MEASUREMENT FACILITY ->
DEV TYPE VOLSER IOREQST SEC %Q %ER R %LK LNK PA %UT ACC FPT DCT CN %CN
0480 OSA 8373 279 .00 .00 1.9 0 1 .00 0 0 0 0 .00
0481 OSA 7989 266 .00 .00 .29 0 1 .00 0 0 0 0 .00
1400 3390 LX1400 785 26 .00 .00 .00 1 6 21 8 0 1 7 18
34C6 3390 VMPG18 595 19 .00 .00 .00 0 6 20 10 0 8 1 3.3
<----------- CPU STATISTICS --------> <-- VECTOR ---> <STORAGE><XSTORE>
NC %CPU %US %EM %WT %SY %SP XSI %SC NV %VT %OT RSTR %ST PSEC %XS XSEC TTM
->11 10H 223 387 98 392 123 367K 98 0 0 0 0 71 3569 99 3428 0.003
<-.. 776 121 474 324 181 53 223K 97 .. 0 0 0 75 2786 98 3186 0.023
---------------------<-- 31 LOG ACTIONS INDICATED -->-----------------------+
For more information on RTM, see
z/VM V4R3.0 RealTime Monitor Function
Level 410
, SC24-6028. The data that RTM reports can be stored in a monitor file
for later reporting. The tool that reports on this data is the Performance Reporting
Facility (PRF). For more information on PRF, see
z/VM V4R3.0 Performance
Reporting Facility Function Level 410
, SC24-6027.
8.1.2 Linux storage management and swapping
The problem of determining the amount of storage required for a Linux machine
is complicated by the way Linux uses storage in the virtual machine. Linux will
use all storage in the machine, either for disk buffers, or for application use. TAR
commands for example, tend to use all the storage in the machine during their
processing. From z/VMs perspective, this means that the
working set of storage
used by the Linux guest is the full complete size of the machine. In many cases,
you can actually get better performance from a Linux virtual machine if it is
defined with a smaller memory size.
Obviously, successful operation of an application running in a small virtual
machine depends on the application. Reducing the size of a virtual machine and
then measuring the performance is an iterative process, and one that has a
distressing trial-and-error feel to it.
If Linux runs out of storage, it will attempt to swap some processes out of the
machines memory. The file used for swapping is identified by a
swapon command.
For Linux machines under z/VM, we recommend you use a z/VM facility called
VDISK in memory to supply swap space to Linux. This facility provides a disk file,
which offers very high performance access because the data exists only in
storage. No main storage resources are used until data is written to the file.
138 Experiences with Oracle for Linux on zSeries
In our configuration we allocated 4 GB of VDISK space for each Linux machine.
To do this we put a REXX exec in the virtual machines PROFILE EXEC file. This
gets executed at logon time, and defines two disk files that will be used as swap
files after Linux boots. The device addresses of 201 and 202 are used in each
Linux machine. They are addresses as /dev/dasdb1 and /dev/dasdc1 in the Linux
machine.
The commands in Example 8-6 on page 138 must be executed in the Linux
machine after boot. We enabled in.rexecd in /etc/inetd.conf and executed the
commands through rexec.
Example 8-5 GETSWAP EXEC added to the Linux machines PROFILE
/* REXX GET Swap Space for LINUX guest */
/* Obtains VDISK in Memory and formats it for swap */
address command
'CP DEFINE VFB-512 201 BLK 4194296'
'ACCESS 201 B'
push 'SWAP1'
push '1'
'FORMAT 201 B (BLK 4096'
push '1'
'RESERVE LINUX SWAP B6'
'RELEASE B'
/* Get another one */
'CP DEFINE VFB-512 202 BLK 4194296'
'ACCESS 202 B'
push 'SWAP2'
push '1'
'FORMAT 202 B (BLK 4096'
push '1'
'RESERVE LINUX SWAP B6'
'RELEASE B'
Example 8-6 SWAPON commands executed in Linux
mkswap /dev/dasdb1
swapon /dev/dasdb1
mkswap /dev/dasdc1
swapon /dev/dasdc1
Example 8-7 CP Q ALLOC PAGE command
q alloc page
EXTENT EXTENT TOTAL PAGES HIGH %
VOLID RDEV START END PAGES IN USE PAGE USED
------ ---- ------ ------ ------ ------ ------ ----

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