Re: [PATCH v2 00/17] Refactor fw_devlink to significantly improve boot time

Saravana Kannan
2020-11-24T17:26:49Z

On Tue, Nov 24, 2020 at 12:29 AM 'Tomi Valkeinen' via kernel-team
<kernel-team@android.com> wrote:
>
> Hi,
>
> On 21/11/2020 04:02, 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.
> >
> > Laurent and Grygorii tested the v1 series and they saw boot time
> > improvment of about 12 seconds and 3 seconds, respectively.
>
> Tested v2 on OMAP4 SDP. With my particular config, boot time to starting init went from 18.5 seconds
> to 12.5 seconds.

Thanks for testing Tomi!

-Saravana