Re: [PATCH v1 00/18] Refactor fw_devlink to significantly improve boot time

Laurent Pinchart
2020-11-06T05:09:48Z

Hi Saravana,

Thank you for working on this !

On Wed, Nov 04, 2020 at 03:23:37PM -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.
>
> Tomi/Laurent/Grygorii,
>
> If you can test this series, that'd be great!

I gave it a try, rebasing my branch from v5.9 to v5.10-rc2 first. On
v5.10-rc2 the kernel dies when booting due to a deadlock (reported by
lockdep, so hopefully not too hard to debug). *sigh*. Fortunately, it
dies after the fw_devlink initialization, so I can still report results.

Before your series:

[ 0.743065] cpuidle: using governor menu
[ 13.350259] No ATAGs?

With your series applied:

[ 0.722670] cpuidle: using governor menu
[ 1.135859] No ATAGs?

That's a very clear improvement :-)

Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> [1] - https://lore.kernel.org/linux-pm/CAGETcx-aiW251dhEXT1GNb9bi6YcX8W=jLBrro5CnPuEjGL09g@mail.gmail.com/
>
> Saravana Kannan (18):
> Revert "driver core: Avoid deferred probe due to fw_devlink_pause/resume()"
> Revert "driver core: Rename dev_links_info.defer_sync to defer_hook"
> Revert "driver core: Don't do deferred probe in parallel with kernel_init thread"
> Revert "driver core: Remove check in driver_deferred_probe_force_trigger()"
> Revert "of: platform: Batch fwnode parsing when adding all top level devices"
> Revert "driver core: fw_devlink: Add support for batching fwnode parsing"
> driver core: Add fwnode_init()
> driver core: Add fwnode link support
> driver core: Allow only unprobed consumers for SYNC_STATE_ONLY device links
> device property: Add fwnode_is_ancestor_of()
> driver core: Redefine the meaning of fwnode_operations.add_links()
> driver core: Add fw_devlink_parse_fwtree()
> driver core: Add fwnode_get_next_parent_dev() helper function
> driver core: Use device's fwnode to check if it is waiting for suppliers
> of: property: Update implementation of add_links() to create fwnode links
> efi: Update implementation of add_links() to create fwnode links
> driver core: Add helper functions to convert fwnode links to device links
> driver core: Refactor fw_devlink feature
>
> drivers/acpi/property.c | 2 +-
> drivers/acpi/scan.c | 2 +-
> drivers/base/core.c | 584 +++++++++++++++++++++-----------
> drivers/base/property.c | 27 ++
> drivers/base/swnode.c | 2 +-
> drivers/firmware/efi/efi-init.c | 31 +-
> drivers/of/dynamic.c | 1 +
> drivers/of/platform.c | 2 -
> drivers/of/property.c | 150 +++-----
> include/linux/device.h | 10 +-
> include/linux/fwnode.h | 66 ++--
> include/linux/of.h | 2 +-
> include/linux/property.h | 2 +
> kernel/irq/irqdomain.c | 2 +-
> 14 files changed, 490 insertions(+), 393 deletions(-)

--
Regards,

Laurent Pinchart