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

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Message-ID: <20110610173345.GA8434@in.ibm.com>
Date:	Fri, 10 Jun 2011 23:03:45 +0530
From:	Ankita Garg <ankita@...ibm.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	Kyungmin Park <kmpark@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	svaidy@...ux.vnet.ibm.com, thomas.abraham@...aro.org
Subject: Re: [PATCH 00/10] mm: Linux VM Infrastructure to support Memory
 Power Management

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.

-- 
Regards,
Ankita Garg (ankita@...ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India
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