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Hey Björn,

On Tue, May 17, 2016 at 11:21 AM, Bjoern Michaelsen <
bjoern.michaelsen@canonical.com> wrote:

Heya Markus,

On Tue, May 17, 2016 at 02:37:02AM +0200, Markus Mohrhard wrote:
The results for the initial build without building or executing the
tests:

real    70m17.990s
user    436m43.860s
sys    28m3.680s

After that the results of a time make, therefore forcing the build of
everything test related and executing the tests:

real    11m30.192s
user    58m43.384s
sys    1m36.876s

Did you by chance have an opportunity to also ran "make" from scratch on
that
machine? I assume/hope it wont take the 70 min + 11 min = 82 min. a
straight
addition would make one assume, because make will use idle job slots
during a
full build.


real    83m37.618s
user    493m30.052s
sys    29m44.404s


And then the following time make (therefore again only executing tests):

real    9m16.741s
user    45m31.208s
sys    0m37.516s




IOW, these number suggest a 82min/70min = 17% overhead in real and a (436 +
58)min/436min = 13% overhead in CPU time -- but I assume the real overhead
in a
build from scratch is smaller than both of that in the real world.


The most critical time I see from in all this is not anything build from
scratch anyway, but the for a simple
touch-one-cxx-recompile-relink-and-then-run-all-the-tests scenarios. So
the:

real    6m37.479s
user    45m4.740s

as an _absolute_ is the key there, I guess.



So for me the problem is that on machines that are much slower it takes
quite some time to execute the tests and that we are going to see people
just skipping the tests if the cost-value relationship becomes too bad. As
mentioned I think we are right now still in an area where it is somewhat ok
but we know that we are adding more and more tests and that it will mean
that the ratio test time/build time will become bigger.



Best,

Bjoern

P.S.: I would have assumed compiling/linking the tests to take much more
time
than running the tests. But it seems with 45min/58min=77% -- most of the
time
is indeed spend on running tests, not building them.

P.S.: For reference, the output of "time make build-nocheck" would be
helpful
      too (aka a noop incremental build time overhead in make/dep parsing
etc.)


real    0m38.787s
user    0m16.300s
sys    0m0.896s

Context


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