Re: [GIT PULL] On-demand device probing

[Noralf TrÃnnes]

Den 17.10.2015 20:45, skrev Rob Clark:
> On Sat, Oct 17, 2015 at 2:27 PM, Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > On Sat, Oct 17, 2015 at 01:54:43PM -0400, Rob Clark wrote:
> > > On Sat, Oct 17, 2015 at 12:56 PM, Greg Kroah-Hartman
> > > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > > > > I'm guessing the time is a matter of probing and undoing the probes
> > > > > rather than slow h/w. We could maybe improve things by making sure
> > > > > drivers move what they defer on to the beginning of probe, but that
> > > > > seems like a horrible, fragile hack.
> > > > How can calling probe and failing cause 2 seconds?  How many different
> > > > probe calls are failing here?  Again, a boot log graph would be great to
> > > > see as it will show the root cause, not just guessing at this.
> > >
> > > just fwiw, but when you have a driver that depends on several other
> > > drivers (which in turn depend on other drivers and so on), the amount
> > > of probe-defer we end up seeing is pretty comical.  Yeah, there
> > > probably is some room to optimize by juggling around order drivers do
> > > things in probe.  But that doesn't solve the fundamental problem with
> > > the current state, about probe order having no clue about
> > > dependencies..
> > I can imagine it is a lot of iterations, but how long does it really
> > take?  How many different devices are involved that it takes multiple
> > loops in order to finally work out the correct order?  Where is the time
> > delays here, just calling probe() and having it instantly return
> > shouldn't take all that long.
> offhand, I think the dependencies go at *least* three levels deep..
> I'd say, from memory, I see drm/msm taking at least 5 or 6 tries to
> get all the way through requesting it's various different
> regulators/clks/gpios.  I hadn't really paid attention to how many
> tries the drivers I depend on go through.  (Of those, I take clks from
> two different clk drivers (which have dependency on a 3rd clk driver),
> and regulators and gpio's come from at least two places, which in turn
> have dependencies on clks, etc.)  I don't have really good hard
> numbers handy (since my observations of this are w/ console over uart
> which effects timings, and so I see it taking much longer than 2sec)..
> but the 2sec figure that Tomeu mentioned seemed pretty plausible to
> me.
>
> I can try to get better #'s... I should have my kernel hat on at least
> some of the time next week.. but the 2sec figure didn't seem
> unrealistic to me.

Are you saying that the total boot time is increased by 2 sec due to
deferred probing, or that display initialization is happening 2 sec
after it's first try?

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