On Sun, Nov 06, 2011 at 10:24:57PM +0200, Sasha Levin wrote: > On Sun, 2011-11-06 at 09:30 +0200, Michael S. Tsirkin wrote: > > On Fri, Nov 04, 2011 at 04:53:05PM +0200, Sasha Levin wrote: > > > > > > > As you said, the PCI cap list was introduced both to save space (which > > > > > > > is not the motivation here), and because it's a very efficient > > > > > > > > > > > > It's actually pretty inefficient - there's an overhead of 3 bytes for > > > > > > each vendor specific option. > > > > > > > > > > It's efficient because while you pay a small price for each optional > > > > > option it also means that that option is optional and won't clutter the > > > > > config space if it's not really in use. > > > > > > > > I guess my assumption is that most options will be in use, > > > > not discarded dead-ends. > > > > > > I don't know about that. 64 bit features would be pretty rare for now - > > > and I don't think that setting the alignment will be also enabled by > > > default. > > > > Setting the alignment might not be *used* by default but > > I think it must be enabled by default to allow bios access. > > > > > I think that we're looking at it differently because I assume that any > > > feature we add at this point would be optional and used only in specific > > > scenarios, while you think that everything added will be used most of > > > the time. > > > > Options must often be present even if not used. For example, as device > > has no way to know whether a guest will want to program alignment, it > > has to make that option available. > > They should be enabled, but heres the difference between the two > approaches is that if it's cap it simply won't be there, How can it not be there? They layout is specified by host, not by guest. > while in the > other case it would just remain empty at some random offset of the > struct. > > -- > > Sasha. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
