[+cc Christoph, Lucas, Dave, Ben, Alex, Myron] 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. > 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? > > Bjorn
