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

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Message-ID: <20070622190000.GK30033@kernel.dk>
Date:	Fri, 22 Jun 2007 21:00:00 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Kristen Carlson Accardi <kristen.c.accardi@...el.com>
Cc:	jeff@...zik.org, linux-ide@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	htejun@...il.com, arjan@...ux.intel.com
Subject: 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 <jens.axboe@...cle.com> wrote:
> 
> > On Wed, Jun 20 2007, Kristen Carlson Accardi wrote:
> > > 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@...el.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@...el.com>

Will you integrate it into the next posting?

-- 
Jens Axboe

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