Re: [PATCH v1 0/5] Optimize async device suspend/resume

[Saravana Kannan]

On Thu, Nov 14, 2024 at 2:09 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote:
>
> A lot of the details are in patch 4/5 and 5/5. The summary is that
> there's a lot of overhead and wasted work in how async device
> suspend/resume is handled today. I talked about this and otther
> suspend/resume issues at LPC 2024[1].
>
> You can remove a lot of the overhead by doing a breadth first queuing of
> async suspend/resumes. That's what this patch series does. I also
> noticed that during resume, because of EAS, we don't use the bigger CPUs
> as quickly. This was leading to a lot of scheduling latency and
> preemption of runnable threads and increasing the resume latency. So, we
> also disable EAS for that tiny period of resume where we know there'll
> be a lot of parallelism.
>
> On a Pixel 6, averaging over 100 suspend/resume cycles, this patch
> series yields significant improvements:
> +---------------------------+-----------+----------------+------------+-------+
> | Phase                     | Old full sync | Old full async | New full async |
> |                           |               |                | + EAS disabled |
> +---------------------------+-----------+----------------+------------+-------+
> | Total dpm_suspend*() time |        107 ms |          72 ms |          62 ms |
> +---------------------------+-----------+----------------+------------+-------+
> | Total dpm_resume*() time  |         75 ms |          90 ms |          61 ms |
> +---------------------------+-----------+----------------+------------+-------+
> | Sum                       |        182 ms |         162 ms |         123 ms |
> +---------------------------+-----------+----------------+------------+-------+
>
> There might be room for some more optimizations in the future, but I'm
> keep this patch series simple enough so that it's easier to review and
> check that it's not breaking anything. If this series lands and is
> stable and no bug reports for a few months, I can work on optimizing
> this a bit further.
>
> Thanks,
> Saravana
> P.S: Cc-ing some usual suspects you might be interested in testing this
> out.
>
> [1] - https://lpc.events/event/18/contributions/1845/
>
> Saravana Kannan (5):
>   PM: sleep: Fix runtime PM issue in dpm_resume()
>   PM: sleep: Remove unnecessary mutex lock when waiting on parent
>   PM: sleep: Add helper functions to loop through superior/subordinate
>     devs
>   PM: sleep: Do breadth first suspend/resume for async suspend/resume
>   PM: sleep: Spread out async kworker threads during dpm_resume*()
>     phases
>
>  drivers/base/power/main.c | 325 +++++++++++++++++++++++++++++---------

Hi Rafael/Greg,

I'm waiting for one of your reviews before I send out the next version.

-Saravana

>  kernel/power/suspend.c    |  16 ++
>  kernel/sched/topology.c   |  13 ++
>  3 files changed, 276 insertions(+), 78 deletions(-)
>
> --
> 2.47.0.338.g60cca15819-goog
>