Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq_fair()

[Ingo Molnar]

* Michael Wang <wangyun@xxxxxxxxxxxxxxxxxx> wrote:

> v3 change log:
> 	Fix small logical issues (Thanks to Mike Galbraith).
> 	Change the way of handling WAKE.
> 
> This patch set is trying to simplify the select_task_rq_fair() 
> with schedule balance map.
> 
> After get rid of the complex code and reorganize the logical, 
> pgbench show the improvement, more the clients, bigger the 
> improvement.
> 
> 				Prev:		Post:
> 
> 	| db_size | clients |	|  tps  |	|  tps  |
>         +---------+---------+   +-------+       +-------+
>         | 22 MB   |       1 |   | 10788 |       | 10881 |
>         | 22 MB   |       2 |   | 21617 |       | 21837 |
>         | 22 MB   |       4 |   | 41597 |       | 42645 |
>         | 22 MB   |       8 |   | 54622 |       | 57808 |
>         | 22 MB   |      12 |   | 50753 |       | 54527 |
>         | 22 MB   |      16 |   | 50433 |       | 56368 |	+11.77%
>         | 22 MB   |      24 |   | 46725 |       | 54319 |	+16.25%
>         | 22 MB   |      32 |   | 43498 |       | 54650 |	+25.64%
>         | 7484 MB |       1 |   |  7894 |       |  8301 |
>         | 7484 MB |       2 |   | 19477 |       | 19622 |
>         | 7484 MB |       4 |   | 36458 |       | 38242 |
>         | 7484 MB |       8 |   | 48423 |       | 50796 |
>         | 7484 MB |      12 |   | 46042 |       | 49938 |
>         | 7484 MB |      16 |   | 46274 |       | 50507 |	+9.15%
>         | 7484 MB |      24 |   | 42583 |       | 49175 |	+15.48%
>         | 7484 MB |      32 |   | 36413 |       | 49148 |	+34.97%
>         | 15 GB   |       1 |   |  7742 |       |  7876 |
>         | 15 GB   |       2 |   | 19339 |       | 19531 |
>         | 15 GB   |       4 |   | 36072 |       | 37389 |
>         | 15 GB   |       8 |   | 48549 |       | 50570 |
>         | 15 GB   |      12 |   | 45716 |       | 49542 |
>         | 15 GB   |      16 |   | 46127 |       | 49647 |	+7.63%
>         | 15 GB   |      24 |   | 42539 |       | 48639 |	+14.34%
>         | 15 GB   |      32 |   | 36038 |       | 48560 |	+34.75%
> 
> Please check the patch for more details about schedule balance map.

The changes look clean and reasoable, any ideas exactly *why* it 
speeds up?

I.e. are there one or two key changes in the before/after logic 
and scheduling patterns that you can identify as causing the 
speedup?

Such changes also typically have a chance to cause regressions 
in other workloads - when that happens we need this kind of 
information to be able to enact plan-B.

Thanks,

	Ingo
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