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:

quoted

Greg KH wrote:

quoted

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