Greg KH wrote: > On Fri, Nov 07, 2008 at 10:37:55AM +0800, Zhao, Yu wrote: >> Greg KH wrote: >>> On Wed, Oct 22, 2008 at 04:45:31PM +0800, Yu Zhao wrote: >>>> Documentation/kernel-parameters.txt | 10 ++++++++++ >>>> 1 files changed, 10 insertions(+), 0 deletions(-) >>>> >>>> diff --git a/Documentation/kernel-parameters.txt >>>> b/Documentation/kernel-parameters.txt >>>> index 53ba7c7..5482ae0 100644 >>>> --- a/Documentation/kernel-parameters.txt >>>> +++ b/Documentation/kernel-parameters.txt >>>> @@ -1677,6 +1677,16 @@ and is between 256 and 4096 characters. It is >>>> defined in the file >>>> cbmemsize=nn[KMG] The fixed amount of bus space which is >>>> reserved for the CardBus bridge's memory >>>> window. The default value is 64 megabytes. >>>> + assign-mmio=[dddd:]bb [X86] reassign memory resources of all >>>> + devices under bus [dddd:]bb (dddd is the domain >>>> + number and bb is the bus number). >>>> + assign-pio=[dddd:]bb [X86] reassign io port resources of all >>>> + devices under bus [dddd:]bb (dddd is the domain >>>> + number and bb is the bus number). >>>> + align-mmio=[dddd:]bb:dd.f [X86] relocate memory resources of a >>>> + device to minimum PAGE_SIZE alignment (dddd is >>>> + the domain number and bb, dd and f is the bus, >>>> + device and function number). >>> This seems like a big problem. How are we going to know to add these >>> command line options for devices we haven't even seen/known about yet? >>> How do we know the bus ids aren't going to change between boots (hint, >>> they are, pci bus ids change all the time...) >>> We need to be able to do this kind of thing dynamically, not fixed at >>> boot time, which seems way to early to even know about this, right? >>> thanks, >>> greg k-h >> Yes, I totally agree. Doing things dynamically is better. >> >> The purpose of these parameters is to rebalance and align resources for >> device that has BARs encapsulated in various new capabilities (SR-IOV, >> etc.), because most of existing BIOSes don't take care of those BARs. > > But how are you going to know what the proper device ids are going to > be before the machine boots? I don't see how these options are ever > going to work properly for a "real" user. > >> If we do resource rebalance after system is up, do you think there is any >> side effect or impact to other subsystem other than PCI (e.g. MTRR)? > > I don't think so. > >> I haven't had much thinking on the dynamical resource rebalance. If you >> have any idea about this, can you please suggest? > > Yeah, it's going to be hard :) > > 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. Regards, Yu _______________________________________________ Virtualization mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/virtualization
