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    SubjectRe: [ath5k-devel] [PATCH v2] ath5k: disable ASPM
    On Tue, Jun 22, 2010 at 12:31 PM, Johannes Stezenbach <js@sig21.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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