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

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Message-ID: <477D3889.9070301@intel.com>
Date:	Thu, 03 Jan 2008 11:33:29 -0800
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Shaohua Li <shaohua.li@...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

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?

Cheers,

Auke
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