linux-kernel - Re: [PATCH] dd: Invoke one probe retry cycle after every initcall level

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Message-ID: <de9fc0924f73bc26e067cce6c18d2714@codeaurora.org>
Date:   Thu, 02 Aug 2018 15:20:47 -0700
From:   Sodagudi Prasad <psodagud@...eaurora.org>
To:     gregkh@...uxfoundation.org, rafael@...nel.org,
        rishabhb@...eaurora.org
Cc:     tsoni@...eaurora.org, Vikram Mulukutla <markivx@...eaurora.org>,
        linux-kernel@...r.kernel.org, ckadabi@...eaurora.org,
        psodagud@...eaurora.org
Subject: Re: [PATCH] dd: Invoke one probe retry cycle after every initcall
 level

> 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.

> 
>> 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.

-thanks, Prasad
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