Re: [PATCH v1 00/18] Refactor fw_devlink to significantly improve boot time

Saravana Kannan
2020-11-06T08:36:48Z

On Thu, Nov 5, 2020 at 9:09 PM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Saravana,
>
> Thank you for working on this !
>
> On Wed, Nov 04, 2020 at 03:23:37PM -0800, Saravana Kannan wrote:
> > The current implementation of fw_devlink is very inefficient because it
> > tries to get away without creating fwnode links in the name of saving
> > memory usage. Past attempts to optimize runtime at the cost of memory
> > usage were blocked with request for data showing that the optimization
> > made significant improvement for real world scenarios.
> >
> > We have those scenarios now. There have been several reports of boot
> > time increase in the order of seconds in this thread [1]. Several OEMs
> > and SoC manufacturers have also privately reported significant
> > (350-400ms) increase in boot time due to all the parsing done by
> > fw_devlink.
> >
> > So this patch series refactors fw_devlink to be more efficient. The key
> > difference now is the addition of support for fwnode links -- just a few
> > simple APIs. This also allows most of the code to be moved out of
> > firmware specific (DT mostly) code into driver core.
> >
> > This brings the following benefits:
> > - Instead of parsing the device tree multiple times (complexity was
> > close to O(N^3) where N in the number of properties) during bootup,
> > fw_devlink parses each fwnode node/property only once and creates
> > fwnode links. The rest of the fw_devlink code then just looks at these
> > fwnode links to do rest of the work.
> >
> > - Makes it much easier to debug probe issue due to fw_devlink in the
> > future. fw_devlink=on blocks the probing of devices if they depend on
> > a device that hasn't been added yet. With this refactor, it'll be very
> > easy to tell what that device is because we now have a reference to
> > the fwnode of the device.
> >
> > - Much easier to add fw_devlink support to ACPI and other firmware
> > types. A refactor to move the common bits from DT specific code to
> > driver core was in my TODO list as a prerequisite to adding ACPI
> > support to fw_devlink. This series gets that done.
> >
> > Tomi/Laurent/Grygorii,
> >
> > If you can test this series, that'd be great!
>
> I gave it a try, rebasing my branch from v5.9 to v5.10-rc2 first. On
> v5.10-rc2 the kernel dies when booting due to a deadlock (reported by
> lockdep, so hopefully not too hard to debug). *sigh*. Fortunately, it
> dies after the fw_devlink initialization, so I can still report results.

Phew! For a sec I thought you said fw_devlink was causing a deadlock.

>
> Before your series:
>
> [ 0.743065] cpuidle: using governor menu
> [ 13.350259] No ATAGs?
>
> With your series applied:
>
> [ 0.722670] cpuidle: using governor menu
> [ 1.135859] No ATAGs?
>
> That's a very clear improvement :-)

Thanks for testing. Great to hear it's helping!

> Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

I'll add it to my v2 series.

-Saravana