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

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