On Thu, Nov 5, 2020 at 9:09 PM Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > 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. Phew! For a sec I thought you said fw_devlink was causing a deadlock. > > 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 :-) Thanks for testing. Great to hear it's helping! > Tested-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> I'll add it to my v2 series. -Saravana
