Test Suite - Performance

Boot Time

Before a test can be run all the VMs are (re)booted. Consequently one obvious way to speed up testing is to reduce the amount of time it takes to boot:

• make the boot faster - it should be around 1s

• boot several machines in parallel - however booting is CPU intensive (see below for analysis)

To determine where a VM is spending its time during boot, use systemd-analyze blame (do several runs, the very first boot does extra configuration so is always be slower):

$ ./testing/utils/kvmsh.py --boot cold w.east systemd-analyze blame
virsh 0.01: starting domain
virsh 15.05: 'login: ' matched after 13.7 seconds
virsh 15.05: waiting 10 seconds for login prompt; 5 seconds for password prompt; 5 seconds for shell prompt
virsh 15.05: 'login: ' matched after 0.0 seconds
virsh 15.09: We're in after 0.5 seconds!

[root@east ~]# systemd-analyze blame
          7.576s network.service
           843ms dev-vda1.device
           781ms initrd-switch-root.service
           776ms systemd-vconsole-setup.service
           679ms sssd.service
           526ms systemd-udev-trigger.service
           235ms sysroot.mount
           180ms dev-mqueue.mount
           174ms dracut-cmdline.service
           170ms kmod-static-nodes.service
           162ms systemd-journald.service
           159ms sys-kernel-debug.mount
           152ms dev-hugepages.mount
           151ms user@0.service
           144ms systemd-tmpfiles-setup-dev.service
           144ms systemd-tmpfiles-setup.service
           143ms systemd-remount-fs.service
           137ms testing.mount
           135ms fedora-readonly.service
           135ms systemd-modules-load.service
           127ms source.mount
           119ms systemd-journal-flush.service
           107ms initrd-parse-etc.service
            ....

Test Time

First to establish a baseline, enumcheck-01, which pretty much nothing, takes ~2s to run the test scripts once things are booted:

w.runner enumcheck-01 32.08/32.05: start running scripts west:west.sh west:final.sh at 2018-10-24 22:00:44.706355
...
w.runner enumcheck-01 34.03/34.00: stop running scripts west:west.sh west:final.sh after 1.5 seconds
...
w.runner enumcheck-01 34.04: stop processing test enumcheck-01 (test 1 of 739) after 34.1 seconds

everything else is slower.

Disk Performance

Something goes here?

Speeding up "make kvm-test" by running things in parallel

Internally kvmrunner.py has two work queues:

• a pool of reboot threads; each thread reboots one domain at a time
• a pool of test threads; each thread runs one test at a time using domains with a unique prefix

The test threads uses the reboot thread pool as follows:

• get the next test
• submit required domains to reboot pool
• wait for domains to reboot
• run test
• repeat

My adjusting KVM_WORKERS and KVM_PREFIXES it is possible:

• speed up test runs
• run independent testsuites in parallel

The reboot thread pool - make KVM_WORKERS=...

Booting the domains is the most CPU intensive part of running a test, and trying to perform too many reboots in parallel will bog down the machine to the point where tests time out and interactive performance becomes hopeless. For this reason a pre-sized pool of reboot threads is used to reboot domains:

• the default is 1 reboot thread limiting things to one domain reboot at a time
• KVM_WORKERS specifies the number of reboot threads, and hence, the reboot parallelism
• increasing this allows more domains to be rebooted in parallel
• however, increasing this consumes more CPU resources

To increase the size of the reboot thread pool set KVM_WORKERS. For instance:

$ grep KVM_WORKERS Makefile.inc.local
KVM_WORKERS=2
$ make kvm-install kvm-test
[...]
runner 0.019: using a pool of 2 worker threads to reboot domains
[...]
runner basic-pluto-01 0.647/0.601: 0 shutdown/reboot jobs ahead of us in the queue
runner basic-pluto-01 0.647/0.601: submitting shutdown jobs for unused domains: road nic north
runner basic-pluto-01 0.653/0.607: submitting boot-and-login jobs for test domains: east west
runner basic-pluto-01 0.654/0.608: submitted 5 jobs; currently 3 jobs pending
[...]
runner basic-pluto-01 28.585/28.539: domains started after 28 seconds

Only if your machine has lots of cores should you consider adjusting this in Makefile.inc.local.

The tests thread pool - make KVM_PREFIXES=...

Note that this is still somewhat experimental and has limitations:

• stopping parallel tests requires multiple control-c's
• since the duplicate domains have the same IP address, things like "ssh east" don't apply; use "make kvmsh-<prefix><domain>" or "sudo virsh console <prefix><domain" or "./testing/utils/kvmsh.py <prefix><domain>".

Tests spend a lot of their time waiting for timeouts or slow tasks to complete. So that tests can be run in parallel the KVM_PREFIX provides a list of prefixes to add to the host names forming unique domain groups that can each be used to run tests:

• the default is no prefix limiting things to a single global domain pool
• KVM_PREFIXES specifies the domain prefixes to use, and hence, the test parallelism
• increasing this allows more tests to be run in parallel
• however, increasing this consumes more memory and context switch resources

For instance, setting KVM_PREFIXES in Makefile.inc.local to specify a unique set of domains for this directory:

$ grep KVM_PREFIX Makefile.inc.local
KVM_PREFIX=a.
$ make kvm-install
[...]
$ make kvm-test
[...]
runner 0.018: using the serial test processor and domain prefix 'a.'
[...]
a.runner basic-pluto-01 0.574: submitting boot-and-login jobs for test domains: a.west a.east

And setting KVM_PREFIXES in Makefile.inc.local to specify two prefixes and, consequently, run two tests in parallel:

$ grep KVM_PREFIX Makefile.inc.local
KVM_PREFIX=a. b.
$ make kvm-install
[...]
$ make kvm-test
[...]
runner 0.019: using the parallel test processor and domain prefixes ['a.', 'b.']
[...]
b.runner basic-pluto-02 0.632/0.596: submitting boot-and-login jobs for test domains: b.west b.east
[...]
a.runner basic-pluto-01 0.769/0.731: submitting boot-and-login jobs for test domains: a.west a.east

creates and uses two dedicated domain/network groups (a.east ..., and b.east ...).

Finally, to get rid of all the domains use:

$ make kvm-uninstall

or even:

$ make KVM_PREFIX=b. kvm-uninstall

Two domain groups (e.x., KVM_PREFIX=a. b.) seems to give the best results.

Recommendations

Some Analysis

The test system:

• 4-core 64-bit intel
• plenty of ram
• the file mk/perf.sh

Increasing the number of parallel tests, for a given number of reboot threads:

• having #cores/2 reboot threads has the greatest impact
• having more than #cores reboot threads seems to slow things down

Increasing the number of reboots, for a given number of test threads:

• adding a second test thread has a far greater impact than adding a second reboot thread - contrast top lines
• adding a third and even fourth test thread - i.e., up to #cores - still improves things

Finally here's some ASCII art showing what happens to the failure rate when the KVM_PREFIX is set so big that the reboot thread pool is kept 100% busy:

                  Fails  Reboots  Time
     ************  127      1     6:35  ****************************************
   **************  135      2     3:33  *********************
  ***************  151      3     3:12  *******************
  ***************  154      4     3:01  ******************

Notice how having more than #cores/2 KVM_WORKERS (here 2) has little benefit and failures edge upwards.

Desktop Development Directory

• reduce build/install time - use only one prefix
• reduce single-test time - boot domains in parallel
• use the non-prefix domains east et.al. so it is easy to access the test domains using tools like ssh

Lets assume 4 cores:

KVM_WORKERS=2
KVM_PREFIX=''

You could also add a second prefix vis:

KVM_PREFIX= '' a.

but that, unfortunately, slows down the the build/install time.

Desktop Baseline Directory

• do not overload the desktop - reduce CPU load by booting sequentially
• reduce total testsuite time - run tests in parallel
• keep separate to development directory above

Lets assume 4 cores

• KVM_WORKERS=1
• KVM_PREFIX= b1. b2.

Dedicated Test Server

• minimize total testsuite time
• maximize CPU use
• assume only testsuite running

Assuming 4 cores:

* KVM_WORKERS=2
* KVM_PREFIX= '' t1. t2. t3.