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

Saravana Kannan
2020-12-09T20:26:19Z

On Wed, Dec 9, 2020 at 10:15 AM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Fri, Nov 20, 2020 at 06:02:15PM -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.
> >
> > Laurent and Grygorii tested the v1 series and they saw boot time
> > improvment of about 12 seconds and 3 seconds, respectively.
>
> Now queued up to my tree. Note, I had to hand-apply patches 13 and 16
> due to some reason (for 13, I have no idea, for 16 it was due to a
> previous patch applied to my tree that I cc:ed you on.)
>
> Verifying I got it all correct would be great :)

A quick diff of drivers/base/core.c between driver-core-testing and my
local tree doesn't show any major diff (only some unrelated comment
fixes). So, it looks fine.

The patch 13 conflict is probably due to having to rebase the v2
series on top of this:
https://lore.kernel.org/lkml/20201104205431.3795207-1-saravanak@google.com/

And looks like Patch 16 was handled fine.

Thanks for applying the series.

-Saravana