linux-kernel - Re: [RFC] PCIE ASPM support

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Date:	Tue, 08 Jan 2008 09:34:43 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	"Kok, Auke" <auke-jan.h.kok@...el.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	linux-pci <linux-pci@...ey.karlin.mff.cuni.cz>,
	Greg KH <greg@...ah.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Subject: Re: [RFC] PCIE ASPM support


On Mon, 2008-01-07 at 10:19 -0800, Kok, Auke wrote:
> Shaohua Li wrote:
> > 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?
> 
> agreed, however this could still be usefull in debugging equipment for the
> experienced user. In any case an easy handle for the driver to dis/enable ASPM
> would certainly help our case, and possibly others.
Then I'll add a config option, and enable the per-device interface with
config enabled.

Thanks,
Shaohua

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