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

Grygorii Strashko
2020-11-06T12:46:37Z

On 06/11/2020 10:36, Saravana Kannan wrote:
> On Thu, Nov 5, 2020 at 9:09 PM Laurent Pinchart
> <laurent.pinchart@ideasonboard.com> 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@ideasonboard.com>
>
> 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@ti.com>

--
Best regards,
grygorii