linux-kernel - Re: /sys/module/pcie_aspm/parameters/policy not writable?

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Date:	Fri, 2 Aug 2013 07:48:37 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Greg KH <greg@...ah.com>,
	kernel list <linux-kernel@...r.kernel.org>,
	Joe Lawrence <joe.lawrence@...atus.com>,
	Myron Stowe <myron.stowe@...hat.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Bruce Allan <bruce.w.allan@...el.com>,
	Carolyn Wyborny <carolyn.wyborny@...el.com>,
	Don Skidmore <donald.c.skidmore@...el.com>,
	Greg Rose <gregory.v.rose@...el.com>,
	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>,
	Alex Duyck <alexander.h.duyck@...el.com>,
	John Ronciak <john.ronciak@...el.com>,
	Tushar Dave <tushar.n.dave@...el.com>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>
Subject: Re: /sys/module/pcie_aspm/parameters/policy not writable?

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

Bjorn
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