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===== Checking job performance =====

Sometimes it is useful to take a closer look on the performance of jobs using the toolbox that Linux has.
We will not describe the details of these tools but just mention a few.

==== Logging in to compute nodes ====

Using the ''ssh'' command line tool it is possible to login into nodes where one of your jobs is running. Please note that you can only login into these nodes. A connection to another node will be refused.

Logging in can be done like this:
<code>
ssh node34
</code>
After this you should obtain a command-line prompt on this node (if you have a job running on that node!). You can use ''squeue'' described earlier to see where your job is running.

==== Checking job performance ====

There are two tools that we will describe on this page. The first is ''top'', the second ''ps''.

=== top ===

The ''top'' tool will show an overview of running processes on the system. You can limit it to your own processes using the ''-u'' option.
The tool will show the CPU utilization at ''%CPU'', the memory usage using ''VIRT'' for virtual (claimed) memory and ''RES'' for memory that is really used.
The CPU usage should ideally be close to 100% for single core tasks and close to  n*100% for multithreaded tasks where n is the number of threads.

To see the individual threads of a multithreaded program you can press shift-H for uppercase H. The q key will exit top.

=== ps ===

Another useful tool is ''ps''. ''ps'' will show processes on the node. To see an extensive overview of the users processes you can use:
<code>
ps -elf | egrep "UID|$USER"
</code>

Please see the man page of ''ps'' for information about the meaning of the fields.