Re: [PATCH 2/5] drivercore: Add driver probe deferral mechanism

Josh Triplett
2011-10-08T18:18:29Z

On Sat, Oct 08, 2011 at 08:55:02AM -0700, Greg KH wrote:
> On Fri, Oct 07, 2011 at 09:03:51PM -0700, Josh Triplett wrote:
> > On Fri, Oct 07, 2011 at 02:23:26PM -0700, Greg KH wrote:
> > > On Fri, Oct 07, 2011 at 01:57:15PM -0700, Josh Triplett wrote:
> > > > On Thu, Oct 06, 2011 at 11:49:28PM -0700, Greg KH wrote:
> > > > > On Fri, Oct 07, 2011 at 10:33:07AM +0500, G, Manjunath Kondaiah wrote:
> > > > > > +config PROBE_DEFER
> > > > > > + bool "Deferred Driver Probe"
> > > > > > + default y
> > > > > > + help
> > > > > > + This option provides deferring driver probe if it has dependency on
> > > > > > + other driver. Without this feature, initcall ordering should be done
> > > > > > + manually to resolve driver dependencies. This feature completely side
> > > > > > + steps the issues by allowing driver registration to occur in any
> > > > > > + order, and any driver can request to be retried after a few more other
> > > > > > + drivers get probed.
> > > > >
> > > > > Why is this even an option? Why would you ever want it disabled? Why
> > > > > does it need to be selected?
> > > > >
> > > > > If you are going to default something to 'y' then just make it so it
> > > > > can't be turned off any other way by just not making it an option at
> > > > > all.
> > > >
> > > > Given that the drivers which use this mechanism will not necessarily get
> > > > built into the kernel, I'd suggest that it should remain optional and
> > > > default to n. Those drivers can then add a dependency on PROBE_DEFER.
> > > > Let's try to avoid adding more infrastructure to the kernel that takes
> > > > up space even when unused; certainly embedded will appreciate not having
> > > > this feature unless a driver needs it.
> > >
> > > How much extra space is this "feature" really?
> >
> > Just checked: 776 bytes, 640 of text and 136 of data. We have kconfig
> > options for comparable amounts.
> >
> > > I don't see it being
> > > anything larger than the amount of memory increase that just happened as
> > > I typed this email as part of the ongoing memory density changes.
> >
> > I don't know about the changes you mean
>
> Moore's law.

Ah, I see. For new systems, sure; for systems or mechanisms with a
pre-existing size constraint, that doesn't help.

> Really, 776 bytes, just always enable it, it's not worth it.

776 bytes alone, no; 776 bytes times the next (or previous) thousand
features, yes.

- Josh Triplett