launchpad-dev team mailing list archive

[Robert Collins <robertc@xxxxxxxxxxxxxxxxx>]

On Tue, Feb 8, 2011 at 10:22 PM, Julian Edwards
<julian.edwards@xxxxxxxxxxxxx> wrote:
> On Tuesday 08 February 2011 02:39:02 Robert Collins wrote:
>> Mid end desktops these days are 8 way machines that should be able to
>> easily do a full test run in < 60 minutes.
>
> Good luck with that.  I've parallelised test runs using virtualisation before
> and you get so much I/O contention that the overall increase in speed is only
> about 10%.
>
> (Using two simultaneous runs on my quad-core Phenom)

I'm certainly aware that there are a bunch of of issues - and previous
experiments here. One of the fairly early steps has to be generating a
load profile for each test process - (python, librarian, appserver,
postgresql etc). We need to then figure out answers to get enough
capacity to scale. For instance, IO load can perhaps be largely
addressed via running the test DB's in a ramdisk. I remember prior
attempts with ramdisks having little impact - but that may can easily
be accounted for if we consider that in a single threaded
configuration we are not bottlenecked on IO: eliminating a
non-bottleneck won't have a dramatic effect. In fact if we're
sufficiently far below the IO thresholds in a single threaded test
config, its plausible we wouldn't see any improvement.

As a datapoint, bzr, which has parallelised its tests for some years
now, scales nearly linearly - and its very IO heavy, writing GB's of
data across an entire test run. If you hit the IO ceiling on a
machine, it stops improving rapidly ;)

-Rob