Posts about end-to-end

What do you want to know about builds?

Mozilla has been quite involved in recent buildbot development, in particular, helping to make it scale across multiple machines. More on this in another post!

Once deployed, these changes will give us the ability to give real time access to various information about our build queue: the list of jobs waiting to start, and which jobs are in progress. This should help other tools like Tinderboxpushlog show more accurate information. One limitation of the upstream work so far is that it only captures a very coarse level of detail about builds: start/end time, and result code is pretty much it. No further detail about the build is captured, like which slave it executed on, what properties it generated (which could include useful information like the URL to the generated binaries), etc.

We've also been exporting a json dump of our build status for many months now. It's been useful for some analysis, but it also has limitations: the data is always at least 5 minutes old by the time you look, and in-progress builds are not represented at all.

We're starting to look at ways of exporting all this detail in a way that's useful to more people. You want to get notified when your try builds are done? You want to look at which test suites are taking the most time? You want to determine how our build times change over time? You want to find out what the last all-green revision was on trunk? We want to make this data available, so anybody can write these tools.

Just how big is that firehose?

I think we have one of the largest buildbot setups out there and we generate a non-trivial amount of data:

  • 6-10 buildbot master processes generating updates, on different machines in 2 or 3 data centers
  • around 130 jobs per hour composed of 4,773 individual steps total per hour. That works out to about 1.4 updates per second that are generated

How you can help

This is where you come in.

I can think of two main classes of interfaces we could set up: a query-type interface where you poll for information that you are interested in, and a notification system where you register a listener for certain types (or all!) events.

What would be the best way for us to make this data available to you? Some kind of REST API? A message or event brokering system? pubsubhubbub?

Is there some type of data or filtering that would be super helpful to you?

Faster build machines, faster end-to-end time

One metric Release Engineering focuses on a lot is the time between a commit to the source tree and when all the builds and tests for that revision are completed. We call this our end-to-end time. Our approach to improving this time has been to identify the longest bits in the total end-to-end time, and to make them faster.

One big chunk of the end-to-end time used to be wait times: how long a build or test waited for a machine to become free. We've addressed this by adding more build and test slaves into the pool.

We've also focused on parallelizing the entire process, so instead of doing this:

before we now do this: after(not exactly to scale, but you get the idea)

Faster builds please!

After splitting up tests and reducing wait times, the longest part of the entire process was now the actual build time.

Last week we added 25 new machines to the pool of build slaves for windows. These new machines are real hardware machines (not VMs), with a quad-core 2.4 GHz processor, 4 GB RAM, and dedicated hard drives.

We've been anticipating that the new build machines can crank out builds much faster.

And they can.

(the break in the graph is the time when mozilla-central was closed due to the PGO link failure bug)

We started rolling the new builders into production on February 22nd (where the orange diamonds start on the graph). You can see the end-to-end time immediately start to drop. From February 1st to the 22nd, our average end-to-end time for win32 on mozilla-central was 4h09. Since the 22nd the average time has dropped down to 3h02. That's over an hour better on average, a 26% improvement.

Faster builds means tests can start faster, which means tests can be done sooner, which means a better end-to-end time. It also means that build machines become free to do another build sooner, and so we're hoping that these faster build machines will also improve our wait time situation (but see below).

Currently we're limited to running the build on these machines with -j1 because of random hangs in the build when using -j2 or higher (bug 524149). Once we fix that, or move to pymake, we should see even better improvements.

What about OSX?

In preparation for deploying these new hardware build machines, we also implemented some prioritization algorithms to choose fast build machines over slow ones, and also to try and choose a machine that has a recent object directory (to make our incremental builds faster). This has helped us out quite a bit on our OSX end-to-end times as well, where we have a mixed pool of xserves and minis doing builds and tests.

OSX End to End time

Simply selecting the right machine for the job reduced our end-to-end time from 3h12 to 2h13, again almost an hour improvement, or 30% better.

What's next?

We have 25 linux machines that should be coming into our production pools this week.

We'll continue to monitor the end-to-end and wait times over the next weeks to see how everything is behaving. One thing I'm watching out for is that having faster builds means we can produce more builds in less time...which means more builds to test! Without enough machines running tests, we may end up making wait times and therefore our end-to-end times worse!

We're already begun work on handling this. Our plan is to start doing the unittest runs on the talos hardware....but that's another post!

Pooling the Talos slaves

One of the big projects for me this quarter was getting our Talos slaves configured as a pool of machines shared across branches. The details are being tracked in bug 488367 for those interested in the details.

This is a continuation of our work on pooling our slaves, like we've done over the past year with our build, unittest, and l10n slaves.

Up until now each branch has had a dedicated set of Mac Minis to run performance tests for just that branch, on five different operating systems. For example, the Firefox 3.0 branch used to have 19 Mac Minis doing regular Talos tests: 4 of each platform (except for Leopard, which had 3). Across our 4 active branches (Firefox 3.0, 3.5, 3.next, and TraceMonkey), we have around 80 minis in total! That's a lot of minis!

What we've been working towards is to put all the Talos slaves into one pool that is shared between all our active branches. Slaves will be given builds to test in FIFO order, regardless of which branch the build is produced on.

This new pool will be....

Faster

With more slaves available to all branches, the time to wait for a free slave will go down, so testing can start more quickly...which means you get your results sooner!

Smarter

It will be able to handle varying load between branches. If there's a lot of activity on one branch, like on the Firefox 3.5 branch before a release, then more slaves will be available to test those builds and won't be sitting idle waiting for builds from low activity branches.

Scalable

We will be able to scale our infrastructure much better using a pooled system. Similar to how moving to pooled build and unittest slaves has allowed us to scale based on number of checkins rather than number of branches, having pooled Talos slaves will allow us to scale our capacity based on number of builds produced rather than the number of branches.

In the current setup, each new release or project branch required an allocation of at least 15 minis to dedicate to the branch.

Once all our Talos slaves are pooled, we will be able to add Talos support for new project or release branches with a few configuration changes instead of waiting for new minis to be provisioned.

This means we can get up and running with new project branches much more quickly!

More Robust

We'll also be in a much better position in terms of maintenance of the machines. When a slave goes offline, the test coverage for any one branch won't be jeopardized since we'll still have the rest of the slaves that can test builds from that branch.

In the current setup, if one or two machines of the same platform needs maintenance on one branch, then our performance test coverage of that branch is significantly impacted. With only one or two machines remaining to run tests on that platform, it can be difficult to determine if a performance regression is caused by a code change, or is caused by some machine issue. Losing two or three machines in this scenario is enough to close the tree, since we no longer have reliable performance data.

With pooled slaves we would see a much more gradual decrease in coverage when machines go offline. It's the difference between losing one third of the machines on your branch, and losing one tenth.

When is all this going to happen?

Some of it has started already! We have a small pool of slaves testing builds from our four branches right now. If you know how to coerce Tinderbox to show you hidden columns, you can take a look for yourself. They're also reporting to the new graph server using machines names starting with 'talos-rev2'.

We have some new minis waiting to be added to the pool. Together with existing slaves, this will give us around 25 machines in total to start off the new pool. This isn't enough yet to be able to test every build from each branch without skipping any, so for the moment the pool will be skipping to the most recent build per branch if there's any backlog.

It's worth pointing out that our current Talos system also skips builds if there's any backlog. However, our goal is to turn off skipping once we have enough slaves in the pool to handle our peak loads comfortably.

After this initial batch is up and running, we'll be waiting for a suitable time to start moving the existing Talos slaves into the pool.

All in all, this should be a big win for everyone!

Parallelizing Unit Tests

Last week we flipped the switch and turned on running unit tests on packaged builds for our mozilla-1.9.1, mozilla-central, and tracemonkey branches.

What this means is that our current unit test builds are uploaded to a web server along with all their unit tests. Another machine will then download the build and tests, and run various test suites on them.

Splitting up the tests this way allows us to run the test suites in parallel, so the mochitest suite will run on one machine, and all the other suites will be run on another machine (this group of tests is creatively named 'everythingelse' on Tinderbox).

paralleltests

Splitting up the tests is a critical step towards reducing our end-to-end time, which is the total time elapsed between when a change is pushed into one of the source repositories, and when all of the results from that build are available. Up until now, you had to wait for all the test suites to be completed in sequence, which could take over an hour in total. Now that we can split the tests up, the wait time is determined by the longest test suite. The mochitest suite is currently the biggest chunk here, taking somewhere around 35 minutes to complete, and all of the other tests combined take around 20 minutes. One of the next steps for us to do is to look at splitting up the mochitests into smaller pieces.

For the time being, we will continue to run the existing unit tests on the same machine that is creating the build. This is so that we can make sure that running tests on the packaged builds is giving us the same results (there are already some known differences: bug 491675, bug 475383)

Parallelizing the unit tests, and the infrastructure required to run them, is the first step towards achieving a few important goals.

  • Reducing end-to-end time.

  • Running unit tests on debug, as well as on optimized builds. Once we've got both of these going, we can turn off the builds that are currently done solely to be able to run tests on them.

  • Running unit tests on the same build multiple times, to help isolate intermittent test failures.

All of the gory details can be found in bug 383136.