On Wed, Nov 4, 2020 at 3:23 PM Saravana Kannan <saravanak@xxxxxxxxxx> 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! > > Thanks, > Saravana > > [1] - https://lore.kernel.org/linux-pm/CAGETcx-aiW251dhEXT1GNb9bi6YcX8W=jLBrro5CnPuEjGL09g@xxxxxxxxxxxxxx/ Forgot the update this link in the cover letter. Here's a much better link to the thread that discusses boot time regression: https://lore.kernel.org/linux-omap/ea02f57e-871d-cd16-4418-c1da4bbc4696@xxxxxx/ -Saravana
