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

Saravana Kannan
2020-11-21T02:02:44Z

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.

Thanks,
Saravana

[1] - https://lore.kernel.org/linux-pm/CAGETcx-aiW251dhEXT1GNb9bi6YcX8W=jLBrro5CnPuEjGL09g@mail.gmail.com/

v1 -> v2:
Patches 1-6:
- Added the "why" to explain the reverts.
Patch 7:
- Fixed white space comment.
Patch 8:
- Reworded commit text and some function doc.
Patch 11:
- Fixed the build warning this patch would cause by removing a "const".
Patch 12:
- Added/updated documentation.
- Changed flags from u32 to u8.
Patch 13:
- Squashed with Patch 10. Will use v1 patch number for the rest of the diff
descriptions.
Patch 15:
- Removed an unnecessary unlikely()
Patch 17:
- Refactored fw_devlink_create_devlink() to flip the error handling vs
successful paths.
Patch 18:
- Squashed into Patch 17 as requested by Greg.
- Added Tested-by: tags from Laurent and Grygorii.
New Patch 17:
- New patch to delete useless input to add_links()

Saravana Kannan (17):
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() and
fwnode_get_next_parent_dev()
driver core: Redefine the meaning of fwnode_operations.add_links()
driver core: Add fw_devlink_parse_fwtree()
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: Refactor fw_devlink feature
driver core: Delete pointless parameter in fwnode_operations.add_links

drivers/acpi/property.c | 2 +-
drivers/acpi/scan.c | 2 +-
drivers/base/core.c | 555 ++++++++++++++++++++------------
drivers/base/property.c | 52 +++
drivers/base/swnode.c | 2 +-
drivers/firmware/efi/efi-init.c | 32 +-
drivers/of/dynamic.c | 1 +
drivers/of/platform.c | 2 -
drivers/of/property.c | 149 +++------
include/linux/device.h | 10 +-
include/linux/fwnode.h | 73 ++---
include/linux/of.h | 2 +-
include/linux/property.h | 3 +
kernel/irq/irqdomain.c | 2 +-
14 files changed, 495 insertions(+), 392 deletions(-)

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2.29.2.454.gaff20da3a2-goog