Morten Rasmussen <morten.rasmus...@arm.com> writes:
> On Fri, Sep 11, 2015 at 10:05:53AM -0700, bseg...@google.com wrote:
>> Morten Rasmussen <morten.rasmus...@arm.com> writes:
>>
>> > On Fri, Sep 11, 2015 at 08:28:25AM +0800, Yuyang Du wrote:
>> >> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> >> index 119823d..55a7b93 100644
>> >> --- a/include/linux/sched.h
>> >> +++ b/include/linux/sched.h
>> >> @@ -912,7 +912,7 @@ enum cpu_idle_type {
>> >> /*
>> >> * Increase resolution of cpu_capacity calculations
>> >> */
>> >> -#define SCHED_CAPACITY_SHIFT 10
>> >> +#define SCHED_CAPACITY_SHIFT SCHED_RESOLUTION_SHIFT
>> >> #define SCHED_CAPACITY_SCALE (1L << SCHED_CAPACITY_SHIFT)
>> >>
>> >> /*
>> >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> >> index 68cda11..d27cdd8 100644
>> >> --- a/kernel/sched/sched.h
>> >> +++ b/kernel/sched/sched.h
>> >> @@ -40,6 +40,9 @@ static inline void update_cpu_load_active(struct rq
>> >> *this_rq) { }
>> >> */
>> >> #define NS_TO_JIFFIES(TIME) ((unsigned long)(TIME) / (NSEC_PER_SEC
>> >> / HZ))
>> >>
>> >> +# define SCHED_RESOLUTION_SHIFT 10
>> >> +# define SCHED_RESOLUTION_SCALE (1L << SCHED_RESOLUTION_SHIFT)
>> >> +
>> >> /*
>> >> * Increase resolution of nice-level calculations for 64-bit
>> >> architectures.
>> >> * The extra resolution improves shares distribution and load balancing
>> >> of
>> >> @@ -53,16 +56,15 @@ static inline void update_cpu_load_active(struct rq
>> >> *this_rq) { }
>> >> * increased costs.
>> >> */
>> >> #if 0 /* BITS_PER_LONG > 32 -- currently broken: it increases power
>> >> usage under light load */
>> >> -# define SCHED_LOAD_RESOLUTION 10
>> >> -# define scale_load(w) ((w) << SCHED_LOAD_RESOLUTION)
>> >> -# define scale_load_down(w) ((w) >> SCHED_LOAD_RESOLUTION)
>> >> +# define SCHED_LOAD_SHIFT (SCHED_RESOLUTION_SHIFT +
>> >> SCHED_RESOLUTION_SHIFT)
>> >> +# define scale_load(w) ((w) << SCHED_RESOLUTION_SHIFT)
>> >> +# define scale_load_down(w) ((w) >> SCHED_RESOLUTION_SHIFT)
>> >> #else
>> >> -# define SCHED_LOAD_RESOLUTION 0
>> >> +# define SCHED_LOAD_SHIFT (SCHED_RESOLUTION_SHIFT)
>> >> # define scale_load(w) (w)
>> >> # define scale_load_down(w) (w)
>> >> #endif
>> >>
>> >> -#define SCHED_LOAD_SHIFT (10 + SCHED_LOAD_RESOLUTION)
>> >> #define SCHED_LOAD_SCALE (1L << SCHED_LOAD_SHIFT)
>> >>
>> >> #define NICE_0_LOAD SCHED_LOAD_SCALE
>> >
>> > I think this is pretty much the required relationship between all the
>> > SHIFTs and SCALEs that Peter checked for in his #if-#error thing
>> > earlier, so no disagreements from my side :-)
>> > --
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>>
>> SCHED_LOAD_RESOLUTION and the non-SLR part of SCHED_LOAD_SHIFT are not
>> required to be the same value and should not be conflated.
>>
>> In particular, since cgroups are on the same timeline as tasks and their
>> shares are not scaled by SCHED_LOAD_SHIFT in any way (but are scaled so
>> that SCHED_LOAD_RESOLUTION is invisible), changing that part of
>> SCHED_LOAD_SHIFT would cause issues, since things can assume that nice-0
>> = 1024. However changing SCHED_LOAD_RESOLUTION would be fine, as that is
>> an internal value to the kernel.
>>
>> In addition, changing the non-SLR part of SCHED_LOAD_SHIFT would require
>> recomputing all of prio_to_weight/wmult for the new NICE_0_LOAD.
>
> I think I follow, but doesn't that mean that the current code is broken
> too? NICE_0_LOAD changes if you change SCHED_LOAD_RESOLUTION:
>
> #define SCHED_LOAD_SHIFT (10 + SCHED_LOAD_RESOLUTION)
> #define SCHED_LOAD_SCALE (1L << SCHED_LOAD_SHIFT)
>
> #define NICE_0_LOAD SCHED_LOAD_SCALE
> #define NICE_0_SHIFT SCHED_LOAD_SHIFT
>
> To me it sounds like we need to define it the other way around:
>
> #define NICE_0_SHIFT 10
> #define NICE_0_LOAD (1L << NICE_0_SHIFT)
>
> and then add any additional resolution bits from there to ensure that
> NICE_0_LOAD and the prio_to_weight/wmult tables are unchanged.
No, NICE_0_LOAD is supposed to be scale_load(prio_to_weight[nice_0]),
ie including SLR. It has never been clear to me what
SCHED_LOAD_SCALE/SCHED_LOAD_SHIFT were for as opposed to NICE_0_LOAD,
and the new utilization uses of it are entirely unlinked to 1024 == NICE_0
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