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

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Message-ID: <20100623143940.GA5424@sig21.net>
Date:	Wed, 23 Jun 2010 16:39:40 +0200
From:	Johannes Stezenbach <js@...21.net>
To:	"Luis R. Rodriguez" <mcgrof@...il.com>
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 12:38:03PM -0700, Luis R. Rodriguez wrote:
> On Tue, Jun 22, 2010 at 12:37 PM, Luis R. Rodriguez <mcgrof@...il.com> wrote:
> > On Tue, Jun 22, 2010 at 12:31 PM, Johannes Stezenbach <js@...21.net> wrote:
> >>
> >> 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.
> >
> > 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.
> 
> So defaults should always be sane and you should not have to play with
> this stuff, unless you're a hacker, or are testing something for
> development purposes. Tweaking ASPM settings is not something a user
> should have to worry about. Period.

OK, let me put the question another way:

If enabling ASPM comes with a performance penalty (which is not unexpected,
there is usually a tradeoff between performance and power consumption),
do you think a boot time option (pcie_aspm=) or compile time option
(CONFIG_PCIEASPM) is the right user interface?


But meanwhile I found that CONFIG_PCIEASPM has a runtime
interface, /sys/module/pcie_aspm/parameters/policy.
http://lwn.net/Articles/266585/

I have not tested it on my N130 yet.


Johannes
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