[linux-pm] [PATCH 00/10] mm: Linux VM Infrastructure to support Memory Power Management

[Paul E. McKenney]

On Fri, Jun 10, 2011 at 11:03:45PM +0530, Ankita Garg wrote:
> On Fri, Jun 10, 2011 at 10:19:39AM -0700, Paul E. McKenney wrote:
> > On Fri, Jun 10, 2011 at 06:05:35PM +0100, Matthew Garrett wrote:
> > > On Fri, Jun 10, 2011 at 09:55:29AM -0700, Paul E. McKenney wrote:
> > > > On Fri, Jun 10, 2011 at 04:59:54PM +0100, Matthew Garrett wrote:
> > > > > For the server case, the low hanging fruit would seem to be 
> > > > > finer-grained self-refresh. At best we seem to be able to do that on a 
> > > > > per-CPU socket basis right now. The difference between active and 
> > > > > self-refresh would seem to be much larger than the difference between 
> > > > > self-refresh and powered down.
> > > > 
> > > > By "finer-grained self-refresh" you mean turning off refresh for banks
> > > > of memory that are not being used, right?  If so, this is supported by
> > > > the memory-regions support provided, at least assuming that the regions
> > > > can be aligned with the self-refresh boundaries.
> > > 
> > > I mean at the hardware level. As far as I know, the best we can do at 
> > > the moment is to put an entire node into self refresh when the CPU hits 
> > > package C6.
> > 
> > But this depends on the type of system and CPU family, right?  If you
> > can say, which hardware are you thinking of?  (I am thinking of ARM.)
> > 
> 
> And also whether the memory controller is on-chip or off-chip ? As
> package could be in C6, but other packages could be refering memory
> connected to this socket right ? And as Paul mentioned, at this point
> the ARM SoCs that have support for memory power management, have only a
> single node.

I suspect that this will be changing shortly, and that finer-grained
control might be available.

However, there are also use cases where contiguous memory is required from
time to time by media codecs, and being able to use that memory for other
purposes when the media codec is not in use reduced the total amount of
memory required, which reduces power consumption all the time, right?  ;-)

							Thanx, Paul