Date: Tue, 22 Jun 2010 21:31:43 +0200
From: Johannes Stezenbach <js@sig21.net>
To: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: "Luis R. Rodriguez" <mcgrof@gmail.com>,
	Jussi Kivilinna <jussi.kivilinna@mbnet.fi>,
	Maxim Levitsky <maximlevitsky@gmail.com>,
	David Quan <David.Quan@atheros.com>,
	Bob Copeland <me@bobcopeland.com>,
	"Luis R. Rodriguez" <mcgrof@bombadil.infradead.org>,
	ath5k-devel@venema.h4ckr.net, linux-wireless@vger.kernel.org,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Jonathan May <jonathan.may@atheros.com>,
	Tim Gardner <tim.gardner@canonical.com>
Subject: Re: [ath5k-devel] [PATCH v2] ath5k: disable ASPM
Message-ID: <20100622193143.GA17803@sig21.net>
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On Tue, Jun 22, 2010 at 07:44:26PM +0100, Matthew Garrett wrote:
> On Tue, Jun 22, 2010 at 11:28:20AM -0700, Luis R. Rodriguez wrote:
> > 
> > Heh, this whole patch and thread was started because Jussi tested
> > ath5k with  pcie_aspm=force (on a pre PCIE 1.1 device (?)) . I have
> > been trying to explain all along why this is a terrible idea to the
> > point we should probably just remove that code from the kernel. Hence
> > my side rants and explanations to justify my reasonings.
> 
> Well, there's two things here. If you use force then you might get 
> inappropriate ASPM. But if your BIOS enables ASPM on an old device, then 
> booting *without* CONFIG_PCIE_ASPM will leave it turned on, and booting 
> *with* CONFIG_PCIE_ASPM will turn it off. The Kconfig description is 
> confusing - reality is that CONFIG_PCIE_ASPM enables logic that allows 
> the kernel to modify the BIOS default, and disabling it makes the 
> assumption that your BIOS did something sensible.

Does CONFIG_PCIEASPM provide a way for the user to modifiy
the settings at runtime?

I have a Samsung N130 netbook which has a BIOS setting
called "CPU Power Saving Mode".  When enabled it activates
ASPM L1 and L0s for the ethernet chip (Realtek RTL8102e, 100Mbit)
and the PCIE bridge (with the BIOS setting off it's just L1).
The result is that the ethernet througput is reduced to 25Mbit/s.
(The BIOS setting does not activa L0s for the Atheros AR9285 WLAN.)

99,9% of the time I want to enjoy the power savings,
but occationally I have to transfer some bulk data and would
like to switch the setting for a few minutes.

Or, well, ideally I'd like to have power savings _and_ performance
at the same time without any manual intervention.  I'm not sure
if this is a quirk of the N130 or if ASPM L0s always causes
performance degradation?


Thanks
Johannes