[Buildroot] [PATCH] graph-depends: optimize remove_transitive_deps()

[Gustavo Zacarias <gustavo.zacarias@free-electrons.com>]

On 15/12/15 07:21, Thomas Petazzoni wrote:

> For large configurations, the execution time of
> remove_transitive_deps() becomes really high, due to the number of
> nested loops + the is_dep() function being recursive.
>
> For an allyespackageconfig, the remove_extra_deps() function takes 334
> seconds to execute, and the overall time to generate the .dot file is
> 6 minutes and 39 seconds. Here is a timing of the different
> graph-depends steps and the overall execution time:
>
>    Getting dependencies:   42.5735 seconds
>    Turn deps into a dict:   0.0023 seconds
>    Remove extra deps:     334.1542 seconds
>    Get version:            22.4919 seconds
>    Generate .dot:           0.0197 seconds
>
>    real	6m39.289s
>    user	6m16.644s
>    sys	0m8.792s
>
> By adding a very simple cache for the results of is_dep(), we bring
> down the execution time of the "Remove extra deps" step from 334
> seconds to just 4 seconds, reducing the overall execution time to 1
> minutes and 10 seconds:
>
>    Getting dependencies:  42.9546 seconds
>    Turn deps into a dict:  0.0025 seconds
>    Remove extra deps:      4.9643 seconds
>    Get version:           22.1865 seconds
>    Generate .dot:          0.0207 seconds
>
>    real	1m10.201s
>    user	0m47.716s
>    sys	0m7.948s
>
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Tested-by: Gustavo Zacarias <gustavo.zacarias@free-electrons.com>

For a lot of transitive deps (custom package set) the difference is even 
bigger, akin to hours (previous version) vs 2 minutes (patch applied).

Regards.