Re: [PATCH] libata: Power off empty ports

[Tejun Heo <tj@kernel.org>]

Hello,

On Fri, Mar 04, 2011 at 10:47:56AM -0800, Kristen Carlson Accardi wrote:
> > Why not just do the following?
> > 
> > 	scontrol &= ~(0x3 << 8);
> 
> because, the IPM value is meaningless if we have no devices,
> so this is a wasted operation.

What?  You're trying to save one AND operation to a value which is
already in register in libata powersave path?  That's wrong on so many
levels (it's not even a proper optimization, think about it).  Just
make it easier on the eyes.

> This change was tested on Intel's Sandy Bridge platform.  Your power
> savings will depend on how many implemented ports you have, and how
> many are not being used.  For a system I tested with which had 2 ports
> which I could turn off, I saved 300mW.

Can you please test at least on a couple different hardware and make
sure that the port can be brought back after put to sleep?  ie. Verify
that hotplug still works after min_power -> max_performance?  Also,
please add the test results in the patch description.

Thanks.

-- 
tejun