Date:   Fri, 6 Nov 2020 14:46:25 +0200
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Saravana Kannan <saravanak@...gle.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Android Kernel Team <kernel-team@...roid.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v1 00/18] Refactor fw_devlink to significantly improve
 boot time



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

-- 
Best regards,
grygorii

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