Re: /sys/module/pcie_aspm/parameters/policy not writable?

From: Bjorn Helgaas
Date: Fri Aug 02 2013 - 09:49:05 EST

On Thu, Aug 1, 2013 at 8:13 PM, Pavel Machek <pavel@xxxxxx> wrote:

> Hmm. So I've update bios using 7buj28uc.iso . Reverted the patches and
> yes, ping latencies are still bad:

Wow. I can hardly believe how bad this is (assuming Windows has the
same problem). Thanks a lot for checking this out.

>> >> Carolyn's patch will likely work, at least most of the time, but I
>> >> think there's a small possibility that it could cause a conflict
>> >> between the BIOS and the OS over ASPM control, so I'm not 100% in
>> >> support of that approach. A conflict may not happen on your
>> >> machine,
>> >
>> > Can we base it on DMI whitelist?
>> I don't think we can know a priori whether a machine (even your
>> machine) is susceptible to a conflict. But if Carolyn forcibly
> We don't apriori now how broken machines are, true. There are 1000
> ways BIOS can break things. And yes, it will be us breaking the specs
> here. But "useful machine with OS breaking specs" is better than
> "machine useless for ssh".
> _If_ there's a conflict, we can try something else.
> (Has someone really seen a conflict, or is it just theoretical thing?)

Completely theoretical, as far as I know. I don't even know what a
conflict would look like. Maybe some unexpected ASPM enable/disable
from SMM during suspend/resume or something. Things like that would
likely go unnoticed anyway.

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