[Bug 211713] NVME controller failure: resetting

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=211713

--- Comment #24 from Warner Losh <imp at FreeBSD.org> ---
Gen2 PCIe is limited to 2GB/s for that setup. That's your problem. and likely
an indicator of the solution...

When you say 'under ubuntu' is that on the same physical hardware or a
different system? If it is just a reboot between the two performance profiles,
that tells me one thing. If it is in a physically separate box, that tells me
something else.

At work we have some drives that are defective (bad resistors that need to be
swapped out) because they can't keep the link established at x4 PCIe3 speeds.
Either they fall back to x1 PCIe3 speeds or x2 and/or PCIe2 speeds. And when
they do, they aren't super reliable, in addition to being slow.

FreeBSD currently does a poor job of dealing with PCIe errors, so links can get
into crazy states where they perform horribly. Maybe Linux is better able to
reset the links on errors. If so, then that's up the alley of some uncommitted
AER / Link retrain code I've been working on.

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