Red Hat LINUX VIRTUAL SERVER 4.6 - ADMINISTRATION Manuale di Installazione Scaricare il pdf (Pagina 244)

224 z/VM and Linux on IBM System z: The Virtualization Cookbook for Red Hat Enterprise Linux 6.0

15.Verify that the memory has returned:

# cat memory*/state

online

offline

# free -m

total used free shared buffers cached

Mem: 241 165 75 0 18 54

-/+ buffers/cache: 92 148

Swap: 761 0 761

This section has shown how to configure virtual machines with standby memory and how to

“hot-plug” the memory from Linux. Each of the four Linux virtual machines, LINUX01 through

LINUX04, default to 256 MB of memory and can be moved up to 1 GB. However, LINUX02

through LINUX04 require Linux to be shut down, the CP DEFINE STORAGE command to be

run, and Linux to be rebooted. LINUX01 can now have memory added while Linux is running.

This function can increase your server farm’s performance and availability.

13.7 Using the cpuplugd service

The cpuplugd service allows Linux to enable or disable CPUs and memory, based on a set of

rules. It can improve performance by setting the correct number of processors and amount of

memory for Linux systems depending on their current load. It can also prevent the Linux

scheduler from queue balancing in partial load situations.

More information about cpuplugd can be found in Linux on System z Device Drivers,

Features and Commands on Red Hat Enterprise Linux 6, which can be found on the web at

the following address:

http://www.ibm.com/developerworks/linux/linux390/documentation_red_hat.html

13.7.1 Determining the virtual CPUs being used

To determine the virtual CPUs that are being used, perform the following steps:

1. Start an SSH session to a Linux system and determine how many CPUs Linux has online.

Use a short bash script, lscpus, to save typing:

# cd /usr/local/sbin

# vi lscpus

#!/bin/bash

# script to list the number and status of virtual CPUs

for i in /sys/devices/system/cpu/cpu*

echo $i

cat $i/online

done

2. Save the file and the set it to be executable:

# chmod +x lscpus

3. Observe the status of the cpuplugd service:

# service cpuplugd status

cpuplugd (pid 1574) is running...

1 2 ... 239 240 241 242 243 244 245 246 247 248 249 ... 295 296

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Red Hat LINUX VIRTUAL SERVER 4.6 - ADMINISTRATION Manuale di Installazione Pagina 244