Speed on Windows

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Andreas Schnell

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Apr 16, 2021, 11:20:31 AM4/16/21
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Hello,

I moved a small test project to TUP to learn the possibilities and I'm very happy.
The next step would be the migration of a project with around 16000 files on Windows.
What I understood TUP gains most of it's speed by the monitor which is not available on Windows.
What's your opinion/experience on Windows.
Will TUP be faster than MAKE on Windows?
Will NINJA be faster than TUP on Windows?

I know that it depends on the project, but I want to hear a bit of your experience.

Thanks a lot and best regards.

Andreas

Mike Shal

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Apr 19, 2021, 1:23:37 AM4/19/21
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Hi Andreas,

Some background: tup was designed with the file monitor in mind, with the idea that the build system should already know which files the user changed ahead of time, and then the dependency information can be structured in a way to take advantage of that information. I was expecting that 'make' spends too much time calling stat() on a bunch of unnecessary files, and that this would be the bulk of the time savings. But in reality, make also spends a lot of time parsing the Makefiles and processing all the funky variable constructions that people end up with (like a bunch of $(call) and $(eval) and such). Tup separates out the parsing into a separate phase, and so most of the time that can all be skipped. The partial DAG that tup constructs is also much smaller than a full DAG that a make-like system would use, so it needs to do less work overall there.

In practice, I almost never use the file monitor. Without the file monitor, tup defaults to "scanning mode", where it simply walks the whole tree from the top of the tup hierarchy (ie: where 'tup init' was run, and the .tup directory exists). So you can determine how much exactly the monitor would save you by running 'time tup scan'. On Linux at least, even for a reasonably large project (72k files, roughly 5k commands), the scan takes 260ms on my machine, which is noticeable but still low enough that I don't bother running the monitor on it most of the time.

Of course, Windows is pretty notorious for having much worse file I/O than Linux. You can get an idea for the scanning overhead very easily (without writing any Tupfiles) by going to the top of your project directory and doing something like:

$ tup init
$ tup
# Run this once to initialize the database
$ tup
[ tup ] [0.000s] Scanning filesystem...
[ tup ] [0.261s] Reading in new environment variables...
...

The time on the second line (0.261s in this case) is the time it took to scan, which is all the time the monitor would save.

Note that in comparison to something like make or ninja, it is very easy to construct a case where the scanning mode of tup performs very poorly. Make or Ninja will only look at the files that you declare in the Makefile/ninja files, while tup will scan the whole tree, even if you don't have any Tupfiles at all. Tup could certainly be improved in this case but only tracking files that are mentioned in the Tupfiles and/or are detected as dependencies, but again that would only help when scanning, and the upper bound of the benefit is the time it takes scan to run. In my experience (again, on Linux), the time tup saves by using its more intelligent partial-DAG construction more than makes up for the time for the naive scanning algorithm. Not to mention the peace-of-mind of having automated dependency checking!

I'm curious what your results are and if you find the scanning time prohibitive for your project.

-Mike

Andreas Schnell

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Apr 19, 2021, 11:23:31 AM4/19/21
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Hi Mike,

thank you for your great reply. I haven't expected that it's that simple to check the speed which can be saved by monitor.
To provide a better understanding of the following numbers, this is my PC:
Hewlett-Packard HP ZBook 14 G2
Intel Core i7-5600U CPU @ 2.6GHz with 16.0 GB RAM
Samsung SSD 860 QVO 1TB

Mid size Project:
4901 files in 1650 folders -> Scan took 0.7702s

Big Project:
18835 files in 4238 folders -> Scan took 2.0722s

The scan time is the average of 5 scans.

Our actual build system takes for a build without any modification:
Preprocessing, Compile and Link, Postprocessing -> 13 Minutes
Only Compile and Link -> 4 Minutes
But I get at least the same times if one c-file is touched :-D.

I think there is a big potential in TUP for us :-P.

Regards

Andreas
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