On Thu, Jan 28, 2021 at 6:39 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > [+cc Atanas -- thank you very much for the bug report!] > > On Sat, Feb 22, 2020 at 10:58:40AM -0600, Bjorn Helgaas wrote: > > On Wed, Jan 15, 2020 at 04:10:08PM -0600, Bjorn Helgaas wrote: > > > I think we have a problem with link bandwidth change notifications > > > (see https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/pcie/bw_notification.c). > > > > > > Here's a recent bug report where Jan reported "_tons_" of these > > > notifications on an nvme device: > > > https://bugzilla.kernel.org/show_bug.cgi?id=206197 > > > > AFAICT, this thread petered out with no resolution. > > > > If the bandwidth change notifications are important to somebody, > > please speak up, preferably with a patch that makes the notifications > > disabled by default and adds a parameter to enable them (or some other > > strategy that makes sense). > > > > I think these are potentially useful, so I don't really want to just > > revert them, but if nobody thinks these are important enough to fix, > > that's a possibility. > > Atanas is also seeing this problem and went to the trouble of digging > up this bug report: > https://bugzilla.kernel.org/show_bug.cgi?id=206197#c8 > > I'm actually a little surprised that we haven't seen more reports of > this. I don't think distros enable CONFIG_PCIE_BW, but even so, I > would think more people running upstream kernels would trip over it. > But maybe people just haven't turned CONFIG_PCIE_BW on. > > I don't have a suggestion; just adding Atanas to this old thread. > > > > There was similar discussion involving GPU drivers at > > > https://lore.kernel.org/r/20190429185611.121751-2-helgaas@xxxxxxxxxx > > > > > > The current solution is the CONFIG_PCIE_BW config option, which > > > disables the messages completely. That option defaults to "off" (no > > > messages), but even so, I think it's a little problematic. > > > > > > Users are not really in a position to figure out whether it's safe to > > > enable. All they can do is experiment and see whether it works with > > > their current mix of devices and drivers. > > > > > > I don't think it's currently useful for distros because it's a > > > compile-time switch, and distros cannot predict what system configs > > > will be used, so I don't think they can enable it. > > > > > > Does anybody have proposals for making it smarter about distinguishing > > > real problems from intentional power management, or maybe interfaces > > > drivers could use to tell us when we should ignore bandwidth changes? There's also this recently filed bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1447 The root cause of it appears to be related to ASPM. Alex
