linux-kernel - Re: device struct bloat

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Message-Id: <1194342534.6544.25.camel@twins>
Date:	Tue, 06 Nov 2007 10:48:54 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Greg KH <greg@...ah.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oneukum@...e.de>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, apw <apw@...dowen.org>,
	Ingo Molnar <mingo@...e.hu>,
	linux-usb-devel@...ts.sourceforge.net
Subject: Re: device struct bloat

On Mon, 2007-11-05 at 14:49 -0800, Greg KH wrote:
> On Mon, Nov 05, 2007 at 11:57:14AM +0100, Peter Zijlstra wrote:
> > Hmm, the problem seems to be stuff like:
> > 
> > add usb driver to pci
> >   scan pci devices
> >      add usb host controller device
> >         scan usb devices
> >           add usb hub device
> >             scan usb devices
> >               add usb .....
> > 
> > This seems to be able to go on forever, as long as one can cascade usb
> > hubs.
> 
> USB hubs only work 7 deep, so there is a limit.

Ah, missed that bit of knowledge :-)

> > Doesn't seem like an ideal thing to do from a stack space POV either.
> > 
> > Would it be possible to break at the second scan, that is the device
> > probe and stick that into a workqueue or something. Then we'd only ever
> > have driver->device nesting.
> 
> Alan and Oliver have done some work in this area I think, combined with
> the suspend/bind/unbind issues.  I'll let them comment on your patch :)

Great, so the thing I need to make this work nicely is a limited
device->mutex nesting, if these changes result in that we can work
together to finish this conversion.



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