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

[Arjan van de Ven <arjan@linux.intel.com>]

>>>>
>>>
>>> Arjan, are you referring to the fact that Intel/SNB systems can exploit
>>> memory self-refresh only when the entire system goes idle? Is that why
>>> this
>>> patchset won't turn out to be that useful on those platforms?
>>
>> no we can use other things (CKE and co) all the time.
>>
>
> Ah, ok..
>
>> just that we found that statistical grouping gave 95%+ of the benefit,
>> without the cost of being aggressive on going to a 100.00% grouping
>>
>
> And how do you do that statistical grouping? Don't you need patches similar
> to those in this patchset? Or are you saying that the existing vanilla
> kernel itself does statistical grouping somehow?

so the way I scanned your patchset.. half of it is about grouping,
the other half (roughly) is about moving stuff.

the grouping makes total sense to me.
actively moving is the part that I am very worried about; that part burns power to do
(and performance).... for which the ROI is somewhat unclear to me
(but... data speaks. I can easily be convinced with data that proves one way or the other)

is moving stuff around the 95%-of-the-work-for-the-last-5%-of-the-theoretical-gain
or is statistical grouping enough to get > 95% of the gain... without the cost of moving.


>
> Also, I didn't fully understand how NUMA policy will help in this case..
> If you want to group memory allocations/references into fewer memory regions
> _within_ a node, will NUMA policy really help? For example, in this patchset,
> everything (all the allocation/reference shaping) is done _within_ the
> NUMA boundary, assuming that the memory regions are subsets of a NUMA node.
>
> Regards,
> Srivatsa S. Bhat
>