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

[Greg Kroah-Hartman]

On Mon, Nov 18, 2024 at 08:04:26PM -0800, Saravana Kannan wrote:
> 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.

Please feel free to send, it's the middle of the merge window now, and
I'm busy with that for the next 2 weeks, so I can't do anything until
after that.

thanks,

greg k-h