Messages in this thread | | | Subject | Re: Issues with "PCI/LINK: Report degraded links via link bandwidth notification" | From | "Alex G." <> | Date | Tue, 2 Feb 2021 14:25:14 -0600 |
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On 2/2/21 2:16 PM, Bjorn Helgaas wrote: > On Tue, Feb 02, 2021 at 01:50:20PM -0600, Alex G. wrote: >> On 1/29/21 3:56 PM, Bjorn Helgaas wrote: >>> On Thu, Jan 28, 2021 at 06:07:36PM -0600, Alex G. wrote: >>>> 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. >>> >>> I don't want people to have to discover a parameter to solve issues. >>> If there's a parameter, notification should default to off, and people >>> who want notification should supply a parameter to enable it. Same >>> thing for the sysfs idea. >> >> I can imagine cases where a per-port flag would be useful. For example, a >> machine with a NIC and a couple of PCIe storage drives. In this example, the >> PCIe drives downtrain willie-nillie, so it's useful to turn off their >> notifications, but the NIC absolutely must not downtrain. It's debatable >> whether it should be default on or default off. >> >>> I think we really just need to figure out what's going on. Then it >>> should be clearer how to handle it. I'm not really in a position to >>> debug the root cause since I don't have the hardware or the time. >> >> I wonder >> (a) if some PCIe devices are downtraining willie-nillie to save power >> (b) if this willie-nillie downtraining somehow violates PCIe spec >> (c) what is the official behavior when downtraining is intentional >> >> My theory is: YES, YES, ASPM. But I don't know how to figure this out >> without having the problem hardware in hand. >> >>> If nobody can figure out what's going on, I think we'll have to make it >>> disabled by default. >> >> I think most distros do "CONFIG_PCIE_BW is not set". Is that not true? > > I think it *is* true that distros do not enable CONFIG_PCIE_BW. > > But it's perfectly reasonable for people building their own kernels to > enable it. It should be safe to enable all config options. If they > do enable CONFIG_PCIE_BW, I don't want them to waste time debugging > messages they don't expect. > > If we understood why these happen and could filter out the expected > ones, that would be great. But we don't. We've already wasted quite > a bit of Jan's and Atanas' time, and no doubt others who haven't > bothered to file bug reports. > > So I think I'll queue up a patch to remove the functionality for now. > It's easily restored if somebody debugs the problem or adds a > command-line switch or something.
I think it's best we make it a module (or kernel) parameter, default=off for the time being.
Alex
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