Messages in this thread | | | Date | Thu, 10 Sep 2015 04:15:20 +0800 | From | Yuyang Du <> | Subject | Re: [PATCH 5/6] sched/fair: Get rid of scaling utilization by capacity_orig |
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On Tue, Sep 08, 2015 at 01:50:38PM +0100, Dietmar Eggemann wrote: > > It's both a unit and a SCALE/SHIFT problem, SCHED_LOAD_SHIFT and > > SCHED_CAPACITY_SHIFT are defined separately so we must be sure to > > scale the value in the right range. In the case of cpu_usage which > > returns sa->util_avg , it's the capacity range not the load range. > > Still don't understand why it's a unit problem. IMHO LOAD/UTIL and > CAPACITY have no unit.
To be more accurate, probably, LOAD can be thought of as having unit, but UTIL has no unit.
Anyway, those are my definitions:
1) unit, only for LOAD, and SCHED_LOAD_X is the unit (but SCHED_LOAD_RESOLUTION make it also some 2, see below) 2) range, aka, resolution or fix-point percentage (as Ben said) 3) timing ratio, LOAD_AVG_MAX etc, unralated with SCHED_LOAD_X
> >> I always thought that scale_load_down() takes care of that. > > > > AFAIU, scale_load_down is a way to increase the resolution of the > > load not to move from load to capacity > > I tried to figure out why we have this issue when comparing UTIL w/ > CAPACITY and not LOAD w/ CAPACITY: > > Both are initialized like that: > > sa->load_avg = scale_load_down(se->load.weight); > sa->load_sum = sa->load_avg * LOAD_AVG_MAX; > sa->util_avg = scale_load_down(SCHED_LOAD_SCALE); > sa->util_sum = LOAD_AVG_MAX; > > and we use 'se->on_rq * scale_load_down(se->load.weight)' as 'unsigned > long weight' argument to call __update_load_avg() making sure the > scaling differences between LOAD and CAPACITY are respected while > updating sa->load_sum (and sa->load_avg).
Yes, because we used SCHED_LOAD_X as both unit and range for LOAD.
> OTAH, we don't apply a scale_load_down for sa->util_[sum/avg] only a '<< > SCHED_LOAD_SHIFT) / LOAD_AVG_MAX' on sa->util_avg. > So changing '<< SCHED_LOAD_SHIFT' to '* > scale_load_down(SCHED_LOAD_SCALE)' would be the logical thing to do.
Actually, for UTIL, we only need range, so don't conflate with LOAD, what about we get all these clarified by redefining SCHED_LOAD_RESOLUTION as the resolution/range generic macro for LOAD, UTIL, and CAPACITY:
#define SCHED_RESOLUTION_SHIFT 10 #define SCHED_RESOLUTION_SCALE (1L << SCHED_RESOLUTION_SHIFT)
#if 0 /* BITS_PER_LONG > 32 -- currently broken: it increases power usage under light load */ # define scale_load(w) ((w) << SCHED_RESOLUTION_SHIFT) # define scale_load_down(w) ((w) >> SCHED_RESOLUTION_SHIFT) # define SCHED_LOAD_SHIFT (10 + SCHED_RESOLUTION_SHIFT) #else # define scale_load(w) (w) # define scale_load_down(w) (w) # define SCHED_LOAD_SHIFT (10) #endif
#define SCHED_LOAD_SCALE (1L << SCHED_LOAD_SHIFT)
For UTIL, e.g., it will be initiated as: sa->util_avg = SCHED_RESOLUTION_SCALE;
And for capacity, we just use SCHED_RESOLUTION_SHIFT (so SCHED_CAPACITY_SHIFT is not needed).
Thanks, Yuyang
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