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

[Greg Kroah-Hartman]

On Wed, Dec 09, 2020 at 12:24:32PM -0800, Saravana Kannan wrote:
> On Wed, Dec 9, 2020 at 10:15 AM Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxx/
> 
> And looks like Patch 16 was handled fine.

Great, thanks for verifying!

greg k-h