Re: [GIT PULL] PCI fixes for v4.10

From: Bjorn Helgaas
Date: Tue May 02 2017 - 14:49:12 EST

On Tue, May 02, 2017 at 12:49:29PM +0200, Lukas Wunner wrote:
> On Mon, May 01, 2017 at 10:41:20PM -0400, Sinan Kaya wrote:
> > On 5/1/2017 9:54 PM, Lukas Wunner wrote:
> > > (b) ASPM L1 enabled on boot, but disabled after powering off and back on
> > > => I believe Sinan is working on this (+cc).
> >
> > The decision was made not to touch ASPM registers following hotplug insertion
> > unless pcie_aspm.policy=powersave is specified.
> >
> > The discussion is here:
> >
> > This was done to maintain existing behavior and not break things.
> Thanks for the reference, I hadn't followed the discussion in April
> very closely, but I think the outcome of the discussion is unfortunate.
> As can be seen in Ashok's tests, merely turning slot power off and back
> on is sufficient to end up with a setting that draws more power. That
> may be equally surprising for users as the issues would be that we seek
> to avoid with a "safety-first" ASPM policy. In any case it seems
> undesirable.
> I hope this is not the end if it and would like to encourage you to
> keep working on this. Perhaps it is too simple to just define a
> default policy, and what is really needed is a policy that adjusts
> itself dynamically to specific devices or workloads, or that can be
> influenced by device drivers.

It's not the end of the discussion. If you have an alternate
proposal, we'd love to hear it, especially if you implement it.