linux-kernel - Re: [PATCH 16/16 v6] PCI: document the new PCI boot parameters

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Message-ID: <20081211014313.GA4947@yzhao12-linux.sh.intel.com>
Date:	Thu, 11 Dec 2008 09:43:13 +0800
From:	Yu Zhao <yu.zhao@...el.com>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Greg KH <greg@...ah.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"achiang@...com" <achiang@...com>,
	"grundler@...isc-linux.org" <grundler@...isc-linux.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"randy.dunlap@...cle.com" <randy.dunlap@...cle.com>,
	"rdreier@...co.com" <rdreier@...co.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 16/16 v6] PCI: document the new PCI boot parameters

On Fri, Nov 07, 2008 at 12:17:22PM +0800, Matthew Wilcox wrote:
> On Fri, Nov 07, 2008 at 11:40:21AM +0800, Zhao, Yu wrote:
> > Greg KH wrote:
> > >We've thought about this in the past, and even Microsoft said it was
> > >going to happen for Vista, but they realized in the end, like we did a
> > >few years previously, that it would require full support of all PCI
> > >drivers as well (if you rebalance stuff that is already bound to a
> > >driver.)  So they dropped it.
> > >
> > >When would you want to do this kind of rebalancing?  Before any PCI
> > >driver is bound to any devices?  Or afterwards?
> > 
> > I guess if we want the rebalance dynamic, then we should have it full -- 
> > the rebalance would be functional even after the driver is loaded.
> > 
> > But in most cases, there will be problem when we unload driver from a 
> > hard disk controller, etc. We can mount root on a ramdisk and do the 
> > rebalance there, but it's complicated for a real user.
> > 
> > So looks like doing rebalancing before any driver is bound to any device 
> > is also a nice idea, if user can get a shell to do rebalance before 
> > built-in PCI driver grabs device.
> 
> Can we use the suspend/resume code to do this?  Some drivers (sym2 for
> one) would definitely need to rerun some of their init code to cope with
> a BAR address changing.

Yes, that is what I was thinking. But after some grep on the PCI device
drivers, I feel frustrated because all those drivers only do 'ioremap'
once at the 'probe' stage.

I believe this is the only problem that preclude us having the run-time
resource rebalance. And I'm not sure how much effort we can fix it. Any
comments?


Thanks,
Yu
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