Re: [PATCH v1 -next 0/3] Some optimizations about freezer

[Michal Koutný]

Hello.

On Thu, Sep 05, 2024 at 01:41:27PM GMT, Chen Ridong <chenridong@xxxxxxxxxx> wrote:
> We optimized the freezer to reduce redundant loops. We add a selftest to
> ensure our optimizations cause no harm, and we confirmed that the
> performance can be improved.

I think these patches have potential to make the code also cleaner and
better to understand (the numbers from optimization don't impress me
that much at the moment).

I post more comments on the individual patches.


> We tested the following subtree: D, E, F and G each have n children.
>         A
>        / \
>       B   C
>     / | \  \
>     D E F   G
>    /  |  \   \
>  1-n 1-n 1-n  0-n

(Why is the last one different?)

> Our test is to freeze A B C D E F G, and then unfreeze A B C D E F G.

I would say measuring freezing/unfreezing of only A would give better
idea about the impact of the change.
(Going through all descendants manually would unfairly show greater
improvement.)

> We measured the elapsed time.
> 
> 	BEFORE(ns)	AFTER(ns)	SAVED(ns)
> n=10	142679950	139666014	3,013,936
> n=100	199832160	192773032	7,059,128
> n=1000	488595100	414901570	73,693,530

How many tasks were there inside cgroups in this benchmark?

(I assume in practice the freezing time would be dominated by waiting
for tasks' response, so it'd be good to note this beside this result.)

Thanks,
Michal

Attachment: signature.asc
Description: PGP signature