Re: [patch 3/3] Enable Aggressive Link Power management for AHCI controllers.

On Fri, Jun 22 2007, Kristen Carlson Accardi wrote:

On Thu, 21 Jun 2007 15:08:32 +0200
Jens Axboe [off-list ref] wrote:

quoted

On Wed, Jun 20 2007, Kristen Carlson Accardi wrote:

quoted

Enable Aggressive Link Power management for AHCI controllers.

This patch will set the correct bits to turn on Aggressive
Link Power Management (ALPM) for the ahci driver.  This
will cause the controller and disk to negotiate a lower
power state for the link when there is no activity (see
the AHCI 1.x spec for details).  This feature is mutually
exclusive with Hot Plug, so when ALPM is enabled, Hot Plug
is disabled.  ALPM will be enabled by default, but it is
settable via the scsi host syfs interface.  Possible 
settings for this feature are:

Setting		Effect
----------------------------------------------------------
min_power	ALPM is enabled, and link set to enter 
		lowest power state (SLUMBER) when idle
		Hot plug not allowed.

max_performance	ALPM is disabled, Hot Plug is allowed

medium_power	ALPM is enabled, and link set to enter
		second lowest power state (PARTIAL) when
		idle.  Hot plug not allowed.

Signed-off-by:  Kristen Carlson Accardi <kristen.c.accardi@intel.com>

A suggestion (it comes with a patch!) - default to max_power/almp off,
not min_power. For two reasons:

- There's such a big performance difference between the two, you really
  want max_power when booting.

- It's a lot better to default to no change, than default to enabling
  something new.

Sounds reasonable to me.  Distros/users can decide if they want to have
scripts that enable this after boot to run at min_power. 

Exactly, it needs to be handled by some power management daemon anyway
and be integrated with power savings in general. You could use io load
to determine when to enable/disable alpm, for instance.

Acked-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>

Will you integrate it into the next posting?

-- 
Jens Axboe