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So far in this book we have focused primarily on the creation of Xen guest domains (domainU). By this stage it is safe to assume that you now have one or more domainU systems up and running on your server or desktop. Given this assumption, this chapter of Xen Virtualization Essentials will be dedicated to providing an overview of the tools and techniques that may be employed to monitor a Xen based environment.
Why Monitor a Xen Environment?
It is important to keep in mind that Xen is an enterprise level environment capable of supporting complex virtualization configurations. As with any complex system it would be naive to assume that the system will run without the occasional performance issues or problem. Deploying Xen virtualization therefore requires an understanding of the tools and techniques necessary to monitor the running environment, identify performance issues and track down problems.
Obtaining Xen Configuration and System Information
Perhaps the most basic step in monitoring a Xen system or isolating a problem is to get a high level overview of the Xen environment and underlying configuration. This information will be of particular importance when requesting help from a vendor or forum. A good way to obtain this information is to use the xm info command. For example, the following example shows output from xm info on a Red Hat Enterprise Linux 5 (RHEL5) system:
xm info host : localhost.localdomain release : 2.6.18-53.el5xen version : #1 SMP Wed Oct 10 17:06:12 EDT 2007 machine : i686 nr_cpus : 1 nr_nodes : 1 sockets_per_node : 1 cores_per_socket : 1 threads_per_core : 1 cpu_mhz : 2993 hw_caps : 0febfbff:20100000:00000000:00000180:0000a015:00000000:00000001 total_memory : 255 free_memory : 14 xen_major : 3 xen_minor : 1 xen_extra : .0-53.el5 xen_caps : xen-3.0-x86_32p xen_pagesize : 4096 platform_params : virt_start=0xf5800000 xen_changeset : unavailable cc_compiler : gcc version 4.1.2 20070626 (Red Hat 4.1.2-14) cc_compile_by : brewbuilder cc_compile_domain : build.redhat.com cc_compile_date : Wed Oct 10 16:30:55 EDT 2007 xend_config_format : 2
Monitoring Xen Performance with XenMon
The XenMon tool is useful for monitoring the performance Xen domains, particularly when identifying which domains are responsible for the highest I/O or processing loads on a system.
XenMon is started from the command-line using the xenmon.py command. The following figure shows a typical XenMon session:
The XenMon display shows two sets of data. On the left hand side are statistics captured over the preceding 10 seconds and on the right is the data for the last 1 second.
For each domain three sets of data are provided. The first row (the grammatically dubious Gotten) for each domain is the amount of time the domain as spent executing. The Blocked row shows statistics for idle time. Finally, the Waited row indicates the amount of time the domain has been in a wait state. For each category the amount of time spent in the particular mode and the time as a percentage of overall time during the corresponding period (i.e 1 or 10 seconds) is displayed. The final value depends on the category. For Gotten this represents processor time, for Blocked the average blocked time and for Wait the average waiting time.
By default XenMon displays information for CPU 0. If the system has more than one physical CPU then the p and n keys can be used to page through the data for each CPU on the system.
When XenMon is exited (using the q key) a summary of data collected during the monitoring session is displayed:
ms_per_sample = 100 Initialized with 1 cpu CPU Frequency = 2993.98 Event counts: 00000000 Other 00000000 Add Domain 00000000 Remove Domain 00000000 Sleep 00022838 Wake 00022838 Block 00045666 Switch 00000000 Timer Func 00045666 Switch Prev 00045666 Switch Next 00000000 Page Map 00000000 Page Unmap 00000000 Page Transfer processed 182674 total records in 288 seconds (634 per second) woke up 288 times in 288 seconds (1 per second)
XenMon accepts a range of command-line options which control various aspects of the monitoring. For a breakdown of these options simply pass the --help argument through to xenmon.py:
xenmon.py --help
usage: xenmon.py [options]
options:
-h, --help show this help message and exit
-l, --live show the ncurses live monitoring frontend (default)
-n, --notlive write to file instead of live monitoring
-p PREFIX, --prefix=PREFIX
prefix to use for output files
-t DURATION, --time=DURATION
stop logging to file after this much time has elapsed
(in seconds). set to 0 to keep logging indefinitely
-i INTERVAL, --interval=INTERVAL
interval for logging (in ms)
--ms_per_sample=MSPERSAMPLE
determines how many ms worth of data goes in a sample
--cpu=CPU specifies which cpu to display data for
--allocated Display allocated time for each domain
--noallocated Don't display allocated time for each domain
--blocked Display blocked time for each domain
--noblocked Don't display blocked time for each domain
--waited Display waiting time for each domain
--nowaited Don't display waiting time for each domain
--excount Display execution count for each domain
--noexcount Don't display execution count for each domain
--iocount Display I/O count for each domain
--noiocount Don't display I/O count for each domain
Monitoring Performance with XenTop
Anyone who has been using UNIX or Linux for any length of time (particularly since the days before GUI desktop environments) is probably familiar with the top command. This long standing tool is used to display information, such as CPU and memory usage, about processes running on a particular system. One of the best features of top is that is puts the process making the heaviest use of a particular resource at the top of the list. When a system is exhibiting performance degradation the top command is often the first port of call for the experienced system administrator.
XenTop is essentially a Xen version of the original top utility and is used to show information about all the domains running on a particular system.
The XenTop tool is launched by typing xentop as root at the command-line. Whilst xentop can be launched without any command-line options, it is worth knowing that a range of options are available and can be listed using the --help flag:
xentop --help Usage: xentop [OPTION] Displays ongoing information about xen vm resources -h, --help display this help and exit -V, --version output version information and exit -d, --delay=SECONDS seconds between updates (default 3) -n, --networks output vif network data -x, --vbds output vbd block device data -r, --repeat-header repeat table header before each domain -v, --vcpus output vcpu data -b, --batch output in batch mode, no user input accepted -i, --iterations number of iterations before exiting Report bugs to <[email protected]>.
The following figure shows sample output from a XenTop session:
