On Wednesday, December 15, 2010 12:03:15 am Linus Torvalds wrote: > On Tue, Dec 14, 2010 at 10:26 PM, Bjorn Helgaas <bjorn.helgaas@xxxxxx> wrote: > > > > I don't know whether the other patches in this series make you > > unhappy. I'm really not happy with how I implemented the avoidance > > of ACPI devices when doing PCI allocation, but I do think we need > > to avoid them *somehow*, and I was looking for a minimal quick > > fix at this point in the cycle. > > So the "avoid ACPI devices" part makes sense, and doesn't involved > quirks, so I don't hate it at all the same way I hated the HP quirk. > > However, I hate how it makes the allocation logic opaque. You can no > longer tell from the regular non-debug dmesg and the /proc/iomem _why_ > something got allocated the way it did, because there are hidden > rules. That makes things awkward, methinks. > > Also, quite frankly, I wonder what happens after release when somebody > shows another machine that simply stopped working because the > allocation strategy didn't work for it. The hw coverage that -rc6 gets > is tiny compared to a real release. > > IOW, what's the long-term strategy for this? The only sane long-term > strategy I can see is the one we have _always_ done, which is to try > to populate the memory resource tree with what simply matches reality. > The whole "ok, we know the hardware better than the BIOS does" is a > _stable_ strategy. In contrast, the things you propose are NOT stable > strategies, they all depend on basically "we match windows exactly > and/or trust ACPI". Both of which are *known* to be failing models. > > That's why I'm somewhat upset. Your whole strategy seems to depend on > a known broken model. We _know_ ACPI tables are crap much of the time. > So we know that "avoiding ACPI resources" is inevitably insufficient. > > And that's why I hate the "switch everything around" model. Yes, we > have a known way to fix things up - namely to actually detect the > hardware itself properly when firmware inevitably screws up - but the > very act of switching things around will pretty much guarantee that > all our years of effort is of dubious value, and we'll end up finding > other laptops that used to work and no longer does. > > Only switching around when _CRS is used is possible, and shouldn't > cause any regressions if we continue to default to not using _CRS. But > you want to switch that default around at some point, don't you? At > which point we'll be up sh*t creek again. See what I'm saying? > > Which all makes me suspect that we'd be much better off just doing the > bottom-up allocation even for _CRS. And maybe CRS works fine then when > we combine our hardware knowledge with the ACPI region avoidance. ACPI devices tend to be at high addresses, so allocating top-down is definitely more dangerous unless we explicitly avoid them. I should have realized that and done something like patches 1-3 of this series before the top-down patches. Doing it bottom-up would very likely work better than the "top-down without avoiding ACPI regions" model we currently have, at least in the short term. We *would* have to do something to avoid E820 reservations to fix this: https://bugzilla.kernel.org/show_bug.cgi?id=16228, but that's doable. So here's my proposal for .37: - Keep the current state of _CRS enabled by default (for 2008 and newer machines). - Allocate bottom-up always - Avoid E820 reservations That should fix all the regressions I'm aware of. I'll work on the patches this afternoon. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
