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

From: Saravana Kannan <saravanak@google.com>
To: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Len Brown <lenb@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Ard Biesheuvel <ardb@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Marc Zyngier <maz@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Grygorii Strashko <grygorii.strashko@ti.com>,
	Android Kernel Team <kernel-team@android.com>,
	ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-efi <linux-efi@vger.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>
Subject: Re: [PATCH v2 00/17] Refactor fw_devlink to significantly improve boot time
Date: Tue, 24 Nov 2020 09:25:42 -0800	[thread overview]
Message-ID: <CAGETcx_ZSYpyi8M3T9d1vJk0FzxWoFWW6A=f-vK4jtF73SR0cw@mail.gmail.com> (raw)
In-Reply-To: <758a1b59-1033-b0ae-2549-84c8eeea4b11@ti.com>

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