On Fri, Jun 22 2007, Kristen Carlson Accardi wrote:
> On Thu, 21 Jun 2007 15:08:32 +0200
> Jens Axboe <[email protected]> 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 <[email protected]>
> >
> > 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 <[email protected]>
Will you integrate it into the next posting?
--
Jens Axboe
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