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

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Message-ID: <20170502104929.GA14029@wunner.de>
Date:   Tue, 2 May 2017 12:49:29 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     "Raj, Ashok" <ashok.raj@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Yinghai Lu <yinghai@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Keith Busch <keith.busch@...el.com>
Subject: Re: [GIT PULL] PCI fixes for v4.10

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: https://lkml.org/lkml/2017/4/17/255
> 
> 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.

Thanks for your efforts,

Lukas