[Qbs] Qbs (way) faster than cmake (or benchmark issue)

Vincent Hui vincenthk007 at gmail.com
Tue Jul 23 04:49:50 CEST 2019

Hi Chris,

Thank you for your benchmark.

Would you mind writing a blog post to record your benchmark in order to
promote Qbs?

By the way, I think we need to come up with good ideas for promoting Qbs.


On Tue, 23 Jul 2019 at 07:31, Christian Gagneraud <chgans at gmail.com> wrote:

> On Mon, 22 Jul 2019 at 22:10, Oswald Buddenhagen
> <oswald.buddenhagen at gmx.de> wrote:
> >
> > On Mon, Jul 22, 2019 at 11:00:07AM +1200, Christian Gagneraud wrote:
> > > At the 20 jobs mark, cmake start to stagnate, whereas qbs still make
> > > use of parallelism, at the 30 jobs mark, cmake completely stopped
> > > reducing overall build time, whereas qbs start to stagnate. At the 40
> > > jobs mark, both systems are stale.
> > >
> > that means that qbs creates a build graph with fewer bottlenecks. cmake
> > certainly could do that with relatively little effort as well, at the
> > likely cost of slightly increased null rebuild times (due to the graph
> > being bigger).
> Should i plot qbs vs cmake null rebuild times? That would be funny if
> qbs was faster again... :P
> Just kidding...
> I think the build graph generated by cmake is too big/complex.
> By default, Qbs doesn't track dependencies on system header files for
> example.
> We shouldn't see such a big difference b/w cmake/ninja and qbs.
> Although i like Qbs very much, i do not believe that it implements
> revolutionary algorithms compared to ninja.
> Ninja website is actually very interesting (eg. w/ references to
> http://gittup.org/tup/ and https://github.com/apenwarr/redo) and my
> gut feeling is that this tool is really efficient in executing it's
> input.
> I think (on of) the problem is what cmake generates, as mentioned in
> an earlier email, I find suspicious that ninja has to call cmake to
> handle moc. And this moc aggregation is certainly one of the
> bottleneck (again, just gut feelings).
> > some suggestions for making a diagram where the interesting stuff isn't
> > crammed into a narrow strip at the bottom:
> > - a logarithmic job count axis
> Doesn't really help on it's own, but log on both axes kind of do, see
> attached document.
> > - build speed per job vs. job count
> > - cpu utilization per core vs. job count
> The main issue here is that i've used '-j' to control jobs, which is
> not good, i should have used docker --cpus instead.
> Nonetheless all the data is attached if someone fancy some data mining.
> > - <your idea here>
> I don't think i'll spend more time on this. But feel free to play with
> that if you (or anyone else) want.
> https://gitlab.com/chgans/cubicninjas
> Nothing fancy really, it's just a Dockerfile and a build script.
> I've attached the csv files, there's lot of potentially interesting
> data in build-qtcreator-stats.csv (see
> https://linux.die.net/man/1/time, i've dumped everything)
> The other file (build-qtcreator-dstat.csv) is data collected by dstat
> for the whole duration of the builds (see
> https://linux.die.net/man/1/dstat, i've dumped disk, load and cpu
> data).
> Again, it's full of potential useful data, it just needs some mining...
> Docker command:
> cd /path/to/qt-creator
> git clone https://gitlab.com/chgans/cubicninjas.git
> docker build -t cubicninjas cubicninjas
> mkdir builds
> docker run -it -v $PWD:$PWD -w $PWD --mount
> type=tmpfs,destination=/tmp --mount type=tmpfs,destination=$PWD/builds
> cubicninjas $PWD/cubicninjas/build.sh
> basic gnuplot command for build-qtcreator-stats.csv:
> set datafile separator ","
> set logscale x
> set logscale y
> plot 'build-qtcreator-stats.csv' every 2::1 using 2:19 with
> linespoints title 'ninja', '' every 2::0 using 2:19 with linespoints
> title 'qbs'
> Enjoy and my apologies for the grumpy email yesterday.
> Chris
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> Qbs at qt-project.org
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