Re: [PATCH] x86,sched: Fix sched_smt_power_savings totally broken

[Youquan Song <youquan.song@intel.com>]

> I had tested sched_mc_powersavings=2 on dual socket quad core HT
> nehalem.  It worked as expected.  Let me check the
> sched_mc_powersavings=1 case.  I will not be surprised if it is
> broken.
> 
 
In my opinion. When CPU cores > 8, sched_mc will have issue of course.
What's more, when CPU cores increase it will be abviously if following
current CPU power capability calcaluation logic.

If CPU has 8 cores and if HT enabled, its power capability > 9 cores. 
Current logic, HT enable core power capability = 1178,  1178 * 8
/ 1024 > 9.2. So scheduler will try to schedule >8 threads to meet its
power capability before use other socket if sched_mc used.

So it will be better, like this: Of course, It is only sample code
and I do not try it yet.

For MC:
+       if (sched_mc_power_savings)
+               sgs->group_capacity = group->group_weight/2;

For SMT:
+       if (sched_smt_power_savings && !(sd->flags & SD_SHARE_CPUPOWER))
+               sgs->group_capacity = group->group_weight;


Thanks
-Youquan