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

[Grygorii Strashko]

On 06/11/2020 10:36, Saravana Kannan wrote:
> 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.

I've tried your series on top of
521b619acdc8 Merge tag 'linux-kselftest-kunit-fixes-5.10-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest
on am571x-idk

Before:
[    0.049395] cpuidle: using governor menu
[    1.654766] audit: type=2000 audit(0.040:1): state=initialized audit_enabled=0 res=1
[    2.315266] No ATAGs?
[    2.315317] hw-breakpoint: found 5 (+1 reserved) breakpoint and 4 watchpoint registers.
[    2.315327] hw-breakpoint: maximum watchpoint size is 8 bytes.
...
[    6.549595] EXT4-fs (mmcblk0p2): mounted filesystem with ordered data mode. Opts: (null)
[    6.557794] VFS: Mounted root (ext4 filesystem) on device 179:26.
[    6.574103] devtmpfs: mounted
[    6.577749] Freeing unused kernel memory: 1024K
[    6.582433] Run /sbin/init as init process


after:
[    0.049223] cpuidle: using governor menu
[    0.095893] audit: type=2000 audit(0.040:1): state=initialized audit_enabled=0 res=1
[    0.102958] No ATAGs?
[    0.103010] hw-breakpoint: found 5 (+1 reserved) breakpoint and 4 watchpoint registers.
[    0.103020] hw-breakpoint: maximum watchpoint size is 8 bytes.
...
[    3.518623] EXT4-fs (mmcblk0p2): mounted filesystem with ordered data mode. Opts: (null)
[    3.526822] VFS: Mounted root (ext4 filesystem) on device 179:26.
[    3.543128] devtmpfs: mounted
[    3.546781] Freeing unused kernel memory: 1024K
[    3.551463] Run /sbin/init as init process

So, it's much better. Thank you.
Tested-by: Grygorii Strashko <grygorii.strashko@xxxxxx>

--
Best regards,
grygorii