Messages in this thread | | | Subject | Re: Issues with "PCI/LINK: Report degraded links via link bandwidth notification" | From | Alex G <> | Date | Wed, 15 Jan 2020 20:44:21 -0600 |
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Hi Bjorn,
I'm no longer working on this, so my memory may not be up to speed. If the endpoint is causing the bandwidth change, then we should get an _autonomous_ link management interrupt instead. I don't think we report those, and that shouldn't spam the logs
If it's not a (non-autonomous) link management interrupt, then something is causing the downstream port to do funny things. I don't think ASPM is supposed to be causing this.
Do we know what's causing these swings?
For now, I suggest a boot-time parameter to disable link speed reporting instead of a compile time option.
Alex
On 1/15/20 4:10 PM, 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 > > There was similar discussion involving GPU drivers at > https://lore.kernel.org/r/20190429185611.121751-2-helgaas@kernel.org > > 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 >
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