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

From: Lukas Wunner <lukas@wunner.de>
To: Sinan Kaya <okaya@codeaurora.org>
Cc: "Raj, Ashok" <ashok.raj@intel.com>,
	Bjorn Helgaas <helgaas@kernel.org>,
	linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
	Yinghai Lu <yinghai@kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Keith Busch <keith.busch@intel.com>
Subject: Re: [GIT PULL] PCI fixes for v4.10
Date: Tue, 2 May 2017 12:49:29 +0200	[thread overview]
Message-ID: <20170502104929.GA14029@wunner.de> (raw)
In-Reply-To: <65f46b49-950a-270f-8bc4-c3fb7513866e@codeaurora.org>

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