Re: [PATCH 0/18] sched: simplified fork, enable load average into LB and power awareness scheduling

[Alex Shi <alex.shi@intel.com>]

>> now, on the other hand, if you have two threads of a process that
>> share a bunch of data structures, and you'd spread these over 2
>> sockets, you end up bouncing data between the two sockets a lot,
>> running inefficient --> bad for power.
> 
> Yeah, that should be addressed by the NUMA patches people are working on
> right now.


Yes, as to balance/powersaving policy, we can tight pack tasks firstly,
then NUMA balancing will make memory follow us.

BTW, NUMA balancing is more related with page in memory. not LLC.
> 
>> having said all this, if you have to tasks that don't have such
>> cache effects, the most efficient way of running things will be on 2
>> hyperthreading halves... it's very hard to beat the power efficiency
>> of that. But this assumes the tasks don't compete with resources much
>> on the HT level, and achieve good scaling. and this still has to
>> compete with "race to halt", because if you're done quicker, you can
>> put the memory in self refresh quicker.
> 
> Right, how are we addressing the breakeven in that case? AFAIK, we
> do schedule them now on two different cores (not HT threads, i.e. no
> resource sharing besides L2) so that we get done faster, i.e. race to

that's balance policy for. :)
> idle in the performance case. And in the powersavings' case we leave
> them as tightly packed as possible.
>