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

[Peter Zijlstra]

On Mon, 2012-01-09 at 19:14 -0500, Youquan Song wrote:
> Fine, I will base your suggestion to develop another patch soon.
> 

> 
> @@ -3923,6 +3923,10 @@ static inline void update_sg_lb_stats(struct
> sched_domain *sd,
>                                                 SCHED_POWER_SCALE);
>         if (!sgs->group_capacity)
>                 sgs->group_capacity = fix_small_capacity(sd, group);
> +
> +       if (sched_smt_power_savings)
> +               sgs->group_capacity *= 2; 

Note, this has the hard-coded assumption you only have 2 threads per
core, which while true for intel, isn't true in general. I think you
meant to write *= group->group_weight or somesuch.

Also, you forgot to limit this to the SD_SHARE_CPUPOWER domain, you're
now doubling the capacity for all domains.

Furthermore, have a look at the SD_PREFER_SIBLING logic and make sure
you're not fighting that.
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