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

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Date:   Wed, 9 Dec 2020 19:16:14 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        kernel-team@...roid.com, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 00/17] Refactor fw_devlink to significantly improve
 boot time

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 :)

thanks,

greg k-h