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Running tests in parallel on a grid
The “queuesystem” configuration

Introduction
When you have more than one machine at your disposal for testing purposes, it is very beneficial to be able to utilise all of them from the same test run. “Grid Engine” software allows you to do this, so that tests can run in parallel across a network. This greatly speeds up testing, naturally, and means far more tests (or longer tests) can be run with somebody waiting on the results.
TextTest's queuesystem configuration is enabled by setting the config file entry “config_module” to “queuesystem”. It operates against an abstract grid engine, which is basically a Python API. Two implementations of this are provided, for the free open source grid engine SGE (which sadly doesn't work on Windows) and Platform Computing's LSF (which does, but costs money). You choose between these by setting the config file entry “queue_system_module” to “SGE” or “LSF”: it defaults to “SGE”.
By default, it will submit all tests to the grid engine. It is still possible to run tests locally as with the default configuration, you need to select the option “Run Tests Locally” (-l on the command line). Internally, TextTest in fact submits itself to the grid engine and runs a slave process remotely, which runs the test in question and communicates the result back to the master process via a socket.
As soon as each test finishes, the test will go green or red, and results will be presented. Unlike the default configuration, the tests will not naturally finish in order. Here is a sample screenshot, using SGE:


Some tests have finished and gone green, but others are still running and hence yellow. TextTest reports their state in the grid engine (“RUN”) followed by the machine each is running on in brackets.
Tables for the queuesystem module
As this functionality works with a different configuration module, additional config file entries, running options and support scripts are available, over and above those provided by default:
Queues
A grid engine will be configured to have a number of queues, which will hold jobs (tests in our case) until a CPU becomes available somewhere, and then dispatch them to that machine. These queues also handle job priorities, it is generally possible to set up several queues so that jobs from one will cause jobs from the other to be suspended. In the case of testing, it is often useful to prioritise jobs by how long they are expected to take, so that a one-hour test can be suspended to allow a five-second test to run. To find out more, read the documentation of the grid engine of your choice.
As far as TextTest is concerned, it must decide which queue to submit each test to. The procedure is as follows:
  1. If the option “Request SGE/LSF queue” has been filled in (-q on the command line), that queue will be used.
  2. If the config file setting “default_queue” has been set to something other than its default value (“texttest_default”), that queue will be used.
  3. If neither, the default queue of the queue system will be used, supposing it has one.
It is often useful to write a derived configuration to modify this logic, for example to introduce some mechanism to select queues based on expected time taken.
Resources
Resources are used to specify properties of machines where you wish your job to run. For example, you might want to request a machine running a particular flavour of linux, or you might want a machine with at least 2GB of memory. Such requests are implemented by resources, in both grid engines. Naturally, more details can again be had from the documentation of the queue systems. LSF requests resources via “bsub -R” on the command line, while SGE uses “qsub -l”.
TextTest must choose which resources to request on the command line. The procedure here is to request all of the resources as specified below:
  1. The value of the option “Request SGE/LSF resource”, if it has been filled in (-R on the command line)
  2. The value of the environment variable QUEUE_SYSTEM_RESOURCE, if it has been set in an environment file.
  3. All resources as generated by the performance_test_resource functionality, if enabled (see below).
Multi-platform testing and environment transfer (UNIX)
TextTest will transfer the environment it has read from its environment files to the slave processes it starts. This can cause a problem if the remote machine is running on a different platform. In this case it is necessary to ensure a full correct login remotely. It has been found useful to support the start of a subshell remotely to make this happen: correct logins are often ensured in shell start-up scripts.
To this end, the “login_shell” entry is provided. This defaults to “sh” (Bourne Shell) but can be configured to be whichever shell startup contains your configuration.
Collecting system resource usage with a grid engine
The queuesystem configuration also provides some improvements in default configuration's functionality for comparing system resource usage in tests. This is essentially in the area of the concept of a performance test machine. In the default configuration, tests are run locally, so all we can do is see if our current machine is enabled for performance testing. With a grid engine at our disposal, we can actually request a performance machine for particular tests.
The simplest way to do this is to check the “run on performance machines only” box from the static GUI (“-perf” on the command line). That will make sure the grid engine requests that the test only run on such machines.
It is also possible to say (for CPU time testing only) that once tests take a certain amount of time they should always be run on performance machines only (it is assumed that the performance of the longest tests is generally the most interesting.) This can be done via the setting min_time_for_performance_force.
There is also an additional mechanism for specifying the performance machines, which on SGE has to be used instead. The config file setting 'performance_test_resource' allows you to identify your performance machines via a grid engine resource, for example to say “test performance on all Opteron250 machines”. This is generally easier than writing out a long list of machines, and is compulsory with SGE for more than one machine. With LSF, you can write out the machines as for the default configuration if you want to.
Batch Mode with a grid engine
The queuesystem configuration also provides an improvement to the batch mode functionality for unattended runs. This basically involves adding a horizon when all remaining tests are killed off and reported as unfinished. This will be done if it receives the signal SIGUSR2 on UNIX.
Both grid engines can be set up to send this signal at a particular time themselves, which involves submitting the TextTest batch run itself to the grid engine. In LSF, use “bsub -t 8:00” to send SIGUSR2 to the job at 8am the next morning. In SGE, use “qsub -notify”, and then call “qdel” for the job at the allotted time: this will also cause the signal to be sent.
CPULIMIT, RUNLIMIT, kill notification and configuring SGE
Both LSF and SGE have mechanisms to send signals to jobs when they exceed a certain time limit. It is possible to configure the queues such that they send SIGXCPU if more than a certain amount of CPU time has been consumed, or SIGUSR1/SIGUSR2 if too much wallclock time is consumed.
TextTest will assume this meaning for these signals and report accordingly. SIGXCPU is always assumed to mean a CPU limit has been reached. SIGUSR2 is interpret to mean a kill notification in SGE and a maximum wallclock time in LSF, while SIGUSR1 is used the other way round in the two grid engines.
To configure SGE to play nicely with this, it's useful to set a notify period of about 60 seconds when jobs are killed (TextTest submits all jobs with the -notify flag). By default, SIGUSR1 is also used to be a suspension notification in SGE, which TextTest does not expect or handle. It's therefore important to disable the NOTIFY_SUSP parameter in SGE if you aren't going to get tests spuriously failing with RUNLIMIT whenever they would be suspended:
When the system under test takes more than one CPU
Both grid engines have functionality for testing systems which are themselves parallel, setting aside several CPUs for the same test. TextTest integrates with this functionality also.
This is basically done via the environment variable QUEUE_SYSTEM_PROCESSES, which says how many CPUs will be needed for each test under that point in the test suite. In LSF this basically translates to the “-n” option to “bsub”. In SGE, you need to use an SGE parallel environment (read the SGE docs!), this is specified via the config file entry “parallel environment name”,
The performance machine functionality described above still works here. In this case TextTest will ask the queue system for all machines that have been used, and only if they are all performance machines will performance be compared.


Last updated: 05 October 2012