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Date:   Fri, 10 Aug 2018 10:19:45 -0700
From:   Sodagudi Prasad <psodagud@...eaurora.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Rishabh Bhatnagar <rishabhb@...eaurora.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        tsoni@...eaurora.org, Vikram Mulukutla <markivx@...eaurora.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ckadabi@...eaurora.org, rjwysocki@...il.com
Subject: Re: [PATCH] dd: Invoke one probe retry cycle after every initcall
 level

On 2018-08-10 00:10, Rafael J. Wysocki wrote:
> On Fri, Aug 10, 2018 at 12:30 AM,  <rishabhb@...eaurora.org> wrote:
>> On 2018-08-06 01:53, Rafael J. Wysocki wrote:
>>> 
>>> On Fri, Aug 3, 2018 at 12:20 AM, Sodagudi Prasad
>>> <psodagud@...eaurora.org> wrote:
>>>>> 
>>>>> From: RAFAEL J. WYSOCKI <rafael@...nel.org>
>>>>> Date: Wed, Aug 1, 2018 at 2:21 PM
>>>>> Subject: Re: [PATCH] dd: Invoke one probe retry cycle after every
>>>>> initcall level
>>>>> To: Rishabh Bhatnagar <rishabhb@...eaurora.org>
>>>>> Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Greg Kroah-Hartman
>>>>> <gregkh@...uxfoundation.org>, Linux Kernel Mailing List
>>>>> <linux-kernel@...r.kernel.org>, ckadabi@...eaurora.org,
>>>>> tsoni@...eaurora.org, Vikram Mulukutla <markivx@...eaurora.org>
>>>>> 
>>>>> 
>>>>> On Wed, Aug 1, 2018 at 11:18 PM,  <rishabhb@...eaurora.org> wrote:
>>>>>> 
>>>>>> 
>>>>>> On 2018-07-24 01:24, Rafael J. Wysocki wrote:
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> On Mon, Jul 23, 2018 at 10:22 PM,  <rishabhb@...eaurora.org> 
>>>>>>> wrote:
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>> On 2018-07-23 04:17, Rafael J. Wysocki wrote:
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> On Thu, Jul 19, 2018 at 11:24 PM, Rishabh Bhatnagar
>>>>>>>>> <rishabhb@...eaurora.org> wrote:
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> Drivers that are registered at an initcall level may have to
>>>>>>>>>> wait until late_init before the probe deferral mechanism can
>>>>>>>>>> retry their probe functions. It is possible that their
>>>>>>>>>> dependencies were resolved much earlier, in some cases even
>>>>>>>>>> before the next initcall level. Invoke one probe retry cycle
>>>>>>>>>> at every _sync initcall level, allowing these drivers to be
>>>>>>>>>> probed earlier.
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> Can you please say something about the actual use case this is
>>>>>>>>> expected to address?
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>> We have a display driver that depends 3 other devices to be
>>>>>>>> probed so that it can bring-up the display. Because of
>>>>> 
>>>>> 
>>>>> dependencies
>>>>>>>> 
>>>>>>>> 
>>>>>>>> not being met the deferral mechanism defers the probes for a 
>>>>>>>> later
>>>>> 
>>>>> 
>>>>> time,
>>>>>>>> 
>>>>>>>> 
>>>>>>>> even though the dependencies might be met earlier. With this
>>>>> 
>>>>> 
>>>>> change
>>>>>>>> 
>>>>>>>> 
>>>>>>>> display can be brought up much earlier.
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> OK
>>>>>>> 
>>>>>>> What runlevel brings up the display after the change?
>>>>>>> 
>>>>>>> Thanks,
>>>>>>> Rafael
>>>>>> 
>>>>>> 
>>>>>> After the change the display can come up after device_initcall 
>>>>>> level
>>>>>> itself.
>>>>>> The above mentioned 3 devices are probed at 0.503253, 0.505210 and
>>>>> 
>>>>> 
>>>>> 0.523264
>>>>>> 
>>>>>> 
>>>>>> secs.
>>>>>> Only the first device is probed successfully. With the current
>>>>>> deferral mechanism the devices get probed again after 
>>>>>> late_initcall
>>>>>> at 9.19 and 9.35 secs. So display can only come up after 9.35 
>>>>>> secs.
>>>>>> With this change the devices are re-probed successfully at 0.60 
>>>>>> and
>>>>>> 0.613 secs. Therefore display can come just after 0.613 secs.
>>>>> 
>>>>> 
>>>>> 
>>>>> OK, so why do you touch the initcall levels earlier than device_?
>>>> 
>>>> 
>>>> 1)      re-probe probing devices in the active list on every level 
>>>> help
>>>> to
>>>> avoid circular dependency pending list.
>>>> 2)      There are so many devices which gets deferred in earlier 
>>>> init
>>>> call
>>>> levels, so we wanted to reprobe them at every successive init call 
>>>> level.
>>> 
>>> 
>>> Do you have specific examples of devices for which that helps?
>>> 
>>>>> 
>>>>>> This change helps in overall android bootup as well.
>>>>> 
>>>>> 
>>>>> 
>>>>> How exactly?
>>>> 
>>>> 
>>>> We have seen less no of re-probes at late_init and most of the 
>>>> driver's
>>>> dependency met earlier than late_init call level. It helped display 
>>>> and
>>>> couple of other drivers by executing the re probe work at every init
>>>> level.
>>> 
>>> 
>>> So I can believe that walking the deferred list on device_initcall 
>>> and
>>> maybe on device_initcall_sync may help, but I'm not quite convinced
>>> that it matters for the earlier initcall levels.
>> 
>> 
>> Many of our drivers are dependent on the regulator and bus driver.
>> Both the regulator and bus driver are probed in the subsys_initcall 
>> level.
>> Now the probe of bus driver requires regulator to be working. If the 
>> probe
>> of
>> bus driver happens before regulator, then bus driver's probe will be
>> deferred and all other device's probes which depend on bus driver will 
>> also
>> be deferred.
>> The impact of this problem is reduced if we have this patch.
> 
> Fair enough, but this information should be there in the changelog of
> your patch.
> 
> And why do you do that for arch_initcall_sync()?
<Prasad> You are right and we can remove arch_initcall_sync().

Added some logging and observed that, none of the devices are re-probed 
in the arch_initcall_sync level.

-Thanks, Prasad
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
Forum,
Linux Foundation Collaborative Project

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