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

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:

quoted

On Fri, Jun 10, 2011 at 06:05:35PM +0100, Matthew Garrett wrote:

quoted

On Fri, Jun 10, 2011 at 09:55:29AM -0700, Paul E. McKenney wrote:

quoted

On Fri, Jun 10, 2011 at 04:59:54PM +0100, Matthew Garrett wrote:

quoted

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