Re: [RFC] PCIE ASPM support

From: Kok, Auke
Date: Thu Jan 03 2008 - 14:34:31 EST

Shaohua Li wrote:
> PCI Express ASPM defines a protocol for PCI Express components in the D0
> state to reduce Link power by placing their Links into a low power state
> and instructing the other end of the Link to do likewise. This
> capability allows hardware-autonomous, dynamic Link power reduction
> beyond what is achievable by software-only controlled power management.
> However, The device should be configured by software appropriately.
> Enabling ASPM will save power, but will introduce device latency.
> This patch adds ASPM support in Linux. It introduces a global policy for
> ASPM, a sysfs file /sys/module/pcie_aspm/parameters/policy can control
> it. The interface can be used as a boot option too. Currently we have
> below setting:
> -default, BIOS default setting
> -powersave, highest power saving mode, enable all available ASPM state
> and clock power management
> -performance, highest performance, disable ASPM and clock power
> management
> By default, the 'default' policy is used currently.
> In my test, power difference between powersave mode and performance mode
> is about 1.3w in a system with 3 PCIE links.
> please review, any comments will be appreciated.

quickly glanced this over since I recently disabled l1 ASPM for the e1000/e1000e
driven 82573 device which has issues with l1 ASPM. that immediately gives me the
question: how can I continue to disable 1l aspm by default for this device using
this infrastructure?

I do like the fact that there is a generic way to re-enable it for the users who
want to use it. Can this change be done when the device is already active? Can you
change this parameter per device/module?

> + /* Clock PM state*/
> + unsigned int clk_pm_capable:1;
> + unsigned int clk_pm_enabled:1;
> + unsigned int bios_clk_state:1;

might want to get rid of these bitfields?


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