Re: [Results] [RFC PATCH v4 00/40] mm: Memory Power Management

From: Srivatsa S. Bhat
Date: Thu Sep 26 2013 - 09:21:07 EST

On 09/26/2013 06:45 AM, Arjan van de Ven wrote:
> On 9/25/2013 4:47 PM, Andi Kleen wrote:
>>> Also, the changelogs don't appear to discuss one obvious downside: the
>>> latency incurred in bringing a bank out of one of the low-power states
>>> and back into full operation. Please do discuss and quantify that to
>>> the best of your knowledge.
>> On Sandy Bridge the memry wakeup overhead is really small. It's on by
>> default
>> in most setups today.
> btw note that those kind of memory power savings are content-preserving,
> so likely a whole chunk of these patches is not actually needed on SNB
> (or anything else Intel sells or sold)

Umm, why not? By consolidating the allocations to fewer memory regions,
this patchset also indirectly consolidates the *references* as well. And
its the lack of memory references that really makes the hardware transition
the unreferenced banks to low-power (content-preserving) states. So from what
I understand, this patchset should provide noticeable benefits on Intel/SNB
platforms as well.

(BTW, even in the prototype powerpc hardware that I mentioned, the primary
memory power savings is expected to come from content-preserving states. So
its not like this patchset was designed only for content-losing/full-poweroff
type of scenarios).

Srivatsa S. Bhat

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