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

[Sodagudi Prasad]

On 2018-08-10 00:10, Rafael J. Wysocki wrote:
> On Fri, Aug 10, 2018 at 12:30 AM,  <rishabhb@xxxxxxxxxxxxxx> wrote:
> > On 2018-08-06 01:53, Rafael J. Wysocki wrote:
> > > On Fri, Aug 3, 2018 at 12:20 AM, Sodagudi Prasad
> > > <psodagud@xxxxxxxxxxxxxx> wrote:
> > > > > From: RAFAEL J. WYSOCKI <rafael@xxxxxxxxxx>
> > > > > 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@xxxxxxxxxxxxxx>
> > > > > Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>, Greg Kroah-Hartman
> > > > > <gregkh@xxxxxxxxxxxxxxxxxxx>, Linux Kernel Mailing List
> > > > > <linux-kernel@xxxxxxxxxxxxxxx>, ckadabi@xxxxxxxxxxxxxx,
> > > > > tsoni@xxxxxxxxxxxxxx, Vikram Mulukutla <markivx@xxxxxxxxxxxxxx>
> > > > >
> > > > >
> > > > > On Wed, Aug 1, 2018 at 11:18 PM,  <rishabhb@xxxxxxxxxxxxxx> wrote:
> > > > > > On 2018-07-24 01:24, Rafael J. Wysocki wrote:
> > > > > > > On Mon, Jul 23, 2018 at 10:22 PM,  <rishabhb@xxxxxxxxxxxxxx> 
> > > > > > > wrote:
> > > > > > > > On 2018-07-23 04:17, Rafael J. Wysocki wrote:
> > > > > > > > > On Thu, Jul 19, 2018 at 11:24 PM, Rishabh Bhatnagar
> > > > > > > > > <rishabhb@xxxxxxxxxxxxxx> 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
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