Re: [RFC] PCIE ASPM support

[Shaohua Li]

On Thu, 2008-01-03 at 11:33 -0800, Kok, Auke wrote:
> 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 used to have a per-device interface, but thought the interface might
be hard to use for users. If we really need the per-device interface, I
can re-add it.

> 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?
Yes, at least in my test.

> Can you
> change this parameter per device/module?
Another way is to provide a helper for driver, and driver disables
specific ASPM states. It sounds better to let driver do the disabling,
as users haven't the knowledge?

Thanks,
Shaohua

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