Re: Issues with "PCI/LINK: Report degraded links via link bandwidth notification"

Alex G.
2021-01-29T00:08:32Z

On 1/28/21 5:51 PM, Sinan Kaya wrote:
> On 1/28/2021 6:39 PM, Bjorn Helgaas wrote:
>> 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.
>
> Hide behind debug or expert option by default? or even mark it as BROKEN
> until someone fixes it?
>
Instead of making it a config option, wouldn't it be better as a kernel
parameter? People encountering this seem quite competent in passing
kernel arguments, so having a "pcie_bw_notification=off" would solve
their problems.

As far as marking this as broken, I've seen no conclusive evidence of to
tell if its a sw bug or actual hardware problem. Could we have a sysfs
to disable this on a per-downstream-port basis?

e.g.
echo 0 > /sys/bus/pci/devices/0000:00:04.0/bw_notification_enabled

This probably won't be ideal if there are many devices downtraining
their links ad-hoc. At worst we'd have a way to silence those messages
if we do encounter such devices.

Alex