linux-kernel - Re: [ath5k-devel] [PATCH v2] ath5k: disable ASPM

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Message-ID: <AANLkTin1fAAgYTYegqaadkYIYP2NXRNRzCR48e-uIgYV@mail.gmail.com>
Date:	Tue, 22 Jun 2010 12:37:01 -0700
From:	"Luis R. Rodriguez" <mcgrof@...il.com>
To:	Johannes Stezenbach <js@...21.net>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	Jussi Kivilinna <jussi.kivilinna@...et.fi>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	David Quan <David.Quan@...eros.com>,
	Bob Copeland <me@...copeland.com>,
	"Luis R. Rodriguez" <mcgrof@...badil.infradead.org>,
	ath5k-devel@...ema.h4ckr.net, linux-wireless@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jonathan May <jonathan.may@...eros.com>,
	Tim Gardner <tim.gardner@...onical.com>
Subject: Re: [ath5k-devel] [PATCH v2] ath5k: disable ASPM

On Tue, Jun 22, 2010 at 12:31 PM, Johannes Stezenbach <js@...21.net> wrote:
> 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?

You can tune ASPM settings at runtime, regardless of CONFIG_PCIEASPM. See:

http://kernel.org/pub/linux/kernel/people/mcgrof/aspm/enable-aspm
http://wireless.kernel.org/en/users/Documentation/ASPM

> 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?

L0s is not going to buy you much gains, getting at least L1 will
however. L0s is just a further enhancement. I recommend you test by
enabling L1 and L0s, check how longer your battery lasts and then test
again with just L1. Then test without both L1 and L0s.

  Luis
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