[BuildStream] Weekly performance update for the Debian-like project

[James Ennis <james ennis codethink co uk>]

Hello,

I've appended a line of results to the tables that I posted to the list 
last week, and also attached the notebook.

See the linked ML post ([0]) if you're struggling to open the notebook 
(the graphs have some fun interactive features).

Results below:

Averages of the show and build times of base-files/base-files.bst [1]:

| Date       |Show (s)| Show with cache (s)| Build (s)| Show once built 
(s)|
|------------|--------|--------------------|----------|--------------------|
| 21/01-27/01| 46.69  | 27.40              | 378.58   | 33.65            
  |
| 28/01-03/02| 46.36  | 27.35              | 383.83   | 33.49            
  |
| 04-02-10/02| 45.72  | 26.53              | 268.70   | 32.68            
  |
| 11/02-17/02| 43.07  | 24.04              | 228.94   | 30.13            
  |
| 18/02-24/02| 40.87  | 22.35              | 228.72   | 28.56            
  |
| 25/02-03/03| 39.33  | 19.85              | 240.00   | 26.44            
  |
| 04/03-10/03| 38.84  | 19.03              | 238.12   | 25.86            
  |
| 11/03-17/03| 38.00  | 18.31              | 301.37   | 25.29            
  |
| 18/03-24/03| 36.67  | 16.90              | 353.67   | 23.71            
  |

Averages of the maximum memory usage for the show and build of 
base-files/base-files.bst:

| Date       |Show (M)| Show with cache (M)| Build (M)| Show once built 
(M)|
|------------|--------|--------------------|----------|--------------------|
| 21/01-27/01| 1084   | 1108               | 1109     | 1110             
  |
| 28/01-03/02| 1083   | 1108               | 1109     | 1110             
  |
| 04-02-10/02| 556    | 581                | 582      | 582              
  |
| 11/02-17/02| 403    | 425                | 425      | 426              
  |
| 18/02-24/02| 410    | 424                | 425      | 425              
  |
| 25/02-03/03| 493    | 514                | 515      | 619              
  |
| 04/03-10/03| 519    | 542                | 543      | 695              
  |
| 11/03-17/03| 521    | 544                | 545      | 697              
  |
| 18/03-24/03| 524    | 547                | 548      | 696              
  |

Please don't be alarmed by the spike in build times, this occurred since 
the landing of Source cache [2]. Basically, local source imports are now 
staged into the the local cache, whereas they were not previously (there 
was a shortcut for local imports, why bother staging this in the local 
cache when it exists within the project...) and because our benchmarks 
were benchmarking a project of 6000 local source imports, we get this 
spike in the build time. Because of this, I've created a project which 
uses 'remote' imports (with a file url) [3], and I will back-generate 
the data for this.

Additionally, all of these benchmarks show that our peak memory 
consumption is creeping back up. I guess this is because we keep making 
these trade-off decisions in favor of a faster runtime, which, for now, 
some of us have agreed that this is not a bad thing, just something that 
people should be aware of. Fortunately, once the !1257 - YAML New World 
Order [4] lands, we should see a significant drop in memory, again (as 
the initial benchmarks of this branch show).

[0] 
https://mail.gnome.org/archives/buildstream-list/2019-February/msg00046.html
[1] https://gitlab.com/jennis/benchmark_debian
[2] https://gitlab.com/BuildStream/buildstream/merge_requests/1124
[3] 
https://gitlab.com/jennis/debian-stretch-bst/tree/jennis/use_remote_file
[4] https://gitlab.com/BuildStream/buildstream/merge_requests/1257