[Scons-users] Performance of version 2.5.0 vs 2.3.0 on Windows host dropped significantly

[Dirk Bächle]

Hi Henrik,

On 08.08.2016 03:23, hmnews at proconx.com wrote:
> Hi all,
>
> We just updated to Scons 2.5.0 after using happily 2.3.0 for years.
>
> Sadly we found performance to have dropped significantly and I wonder
> what the contributing factor could be.
>
> Platform: Windows 10
> Python: 2.7.12 64-bit
>

some more questions about this: Can you compare the times for a build under Linux as well, or do you build under Windows only?

> [...]
>
> However with 2.5.0 execution time blows out to 11.8s, more than 4 times
> longer!!!
>

You say that this is a benchmark project. What happens to the "real" projects? Do they scale, i.e. do they also take about 4 times 
longer each?

> [...]
>
> I appears that Scons takes much longer in 2.5.0 to analyse the build
> targets. This is also apparent when running scons-2.5.0 --debug=prepare
> which takes noticeable longer to to print the file list.
>
> I also compared the dependency tree for both version using --debug=tree
> and they are identical.
>

Good to know, because we have changed "scanning" in a few places, which could've explained the longer times too.

> Has anybody experienced a similar behaviour and is there any tuning
> parameter to make 2.5.0 offer the same performance of 2.3.0?

If there were such a parameter, it would definitely be "on" by default. ;)

>
> Is there any debug option to analyse why Scons 2.5.0 takes such a long
> execution time?

In general, SCons uses most of its time during a "zero build" (nothing to do), "subst"ing variable values. If you're prepared for a 
long and technical read have a look at https://bitbucket.org/scons/scons/wiki/WhySconsIsNotSlow . You might also want to check out 
the "fastcpp" tool at https://bitbucket.org/dirkbaechle/scons_fastcpp to get an idea of how to "tweak" your environment/toolchain to 
get more speed in general.

I hope these first comments already help you a little further.

Best regards,

Dirk


>
> Thanks
>
> Henrik
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