On Thu, May 28, 2020 at 09:33:44AM +0200, Joerg Roedel wrote: > On Wed, May 27, 2020 at 01:18:42PM -0500, Bjorn Helgaas wrote: > > Is this slowdown significant? We already iterate over every device > > when applying PCI_FIXUP_FINAL quirks, so if we used the existing > > PCI_FIXUP_FINAL, we wouldn't be adding a new loop. We would only be > > adding two more iterations to the loop in pci_do_fixups() that tries > > to match quirks against the current device. I doubt that would be a > > measurable slowdown. > > I don't know how significant it is, but I remember people complaining > about adding new PCI quirks because it takes too long for them to run > them all. That was in the discussion about the quirk disabling ATS on > AMD Stoney systems. > > So it probably depends on how many PCI devices are in the system whether > it causes any measureable slowdown. I found this [1] from Paul Menzel, which was a slowdown caused by quirk_usb_early_handoff(). I think the real problem is individual quirks that take a long time. The PCI_FIXUP_IOMMU things we're talking about should be fast, and of course, they're only run for matching devices anyway. So I'd rather keep them as PCI_FIXUP_FINAL than add a whole new phase. Bjorn [1] https://lore.kernel.org/linux-pci/b1533fd5-1fae-7256-9597-36d3d5de9d2a@xxxxxxxxxxxxx/
