Xen Performance Monitor
-----------------------

The xenmon tools make use of the existing xen tracing feature to provide fine
grained reporting of various domain related metrics. It should be stressed that
the xenmon.py script included here is just an example of the data that may be
displayed. The xenbake demon keeps a large amount of history in a shared memory
area that may be accessed by tools such as xenmon.

For each domain, xenmon reports various metrics. One part of the display is a
group of metrics that have been accumulated over the last second, while another
part of the display shows data measured over 10 seconds. Other measurement
intervals are possible, but we have just chosen 1s and 10s as an example.

************* IMPORTANT ****************
Currently, xenmon does NOT support SMP. 
****************************************

Execution Count
---------------
 o The number of times that a domain was scheduled to run (ie, dispatched) over
 the measurement interval


CPU usage
---------
 o Total time used over the measurement interval
 o Usage expressed as a percentage of the measurement interval
 o Average cpu time used during each execution of the domain


Waiting time
------------
This is how much time the domain spent waiting to run, or put another way, the
amount of time the domain spent in the "runnable" state (or on the run queue)
but not actually running. Xenmon displays:

 o Total time waiting over the measurement interval
 o Wait time expressed as a percentage of the measurement interval
 o Average waiting time for each execution of the domain

Blocked time
------------
This is how much time the domain spent blocked (or sleeping); Put another way,
the amount of time the domain spent not needing/wanting the cpu because it was
waiting for some event (ie, I/O). Xenmon reports:

 o Total time blocked over the measurement interval
 o Blocked time expressed as a percentage of the measurement interval
 o Blocked time per I/O (see I/O count below)

Allocation time
---------------
This is how much cpu time was allocated to the domain by the scheduler; This is
distinct from cpu usage since the "time slice" given to a domain is frequently
cut short for one reason or another, ie, the domain requests I/O and blocks.
Xenmon reports:

 o Average allocation time per execution (ie, time slice)
 o Min and Max allocation times

I/O Count
---------
This is a rough measure of I/O requested by the domain. The number of page
exchanges (or page "flips") between the domain and dom0 are counted. The
number of pages exchanged may not accurately reflect the number of bytes
transferred to/from a domain due to partial pages being used by the network
protocols, etc. But it does give a good sense of the magnitude of I/O being
requested by a domain. Xenmon reports:

 o Total number of page exchanges during the measurement interval
 o Average number of page exchanges per execution of the domain

Installation
------------
 - The patches can be found in the patches directory. They are against changeset
   684d8193344209f3bbce4b07977f9d51ec48f63e, but they are fairly trivial and so 
   should be easy to apply manually should a patch fails
 - the patches are in unified diff format, and should apply from the root of
   your xen source tree
 - The tools are in the tools directory. Do a 'make' to build and a 'make install'
   to install them. By default, the executables go in /usr/local/sbin
 - the tools directory does NOT need to be in your xen source tree. You can put
   it anywhere and it should compile as long as Xen is properly installed on
   your machine.

Usage Notes and issues
----------------------
 - Start xenmon by simply running xenmon.py; The xenbake demon is started and
   stopped automatically by xenmon.
 - IMPORTANT: xenbaked uses the processor frequency to convert cycle count to
   timestamps. Therefore, you *MUST* specify the correct frequency for your
   machine, otherwise you will see the time messed up (and utilization not
   adding up to 100%). The frequency can be specified by passing the --cpu_freq
   parameter to xenmon (see xenmon -h).  The frequency should be specified in
   MHz.
 - To see the various options for xenmon, run xenmon -h. Ditto for xenbaked
 - xenmon also has an option (-n) for output log data to a file instead of the
   curses interface
 - Lost trace records are indicated by a blue line at the bottom of the screen.
   When this appears, it means that the data being shown may not be reliable.
   If the number of lost records is excessive (or if the data just seems wrong
   or doesn't add up) then you may need to increase the memory allocated for
   trace buffers. This is done by changing opt_tbuf_size in xen/common/trace.c.
 - NDOMAINS is defined to be 8, but can be changed by recompiling xenbaked
 - Xenmon.py appears to create 1-2% cpu overhead; Part of this is just the
   overhead of the python interpreter. Part of it may be the number of trace
   records being generated. The number of trace records generated can be
   limited by setting the trace mask (with a dom0 Op), which controls which
   events cause a trace record to be emitted.
 - if your terminal screen is not wide enough, xenmon will generate an error
 - To exit xenmon, type 'q'

Future Work
-----------
o RPC interface to allow external entities to programmatically access processed data
o I/O Count batching to reduce number of trace records generated
o Compute processor frequency automatically

Authors
-------
Diwaker Gupta   <diwaker.gupta@hp.com>
Rob Gardner     <rob.gardner@hp.com>
Lucy Cherkasova <lucy.cherkasova.hp.com>

