On 23 March 2015 at 14:19, Peter Zijlstra peterz@infradead.org wrote:
On Fri, Feb 27, 2015 at 04:54:07PM +0100, Vincent Guittot wrote:
unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu);
sa->running_avg_sum += delta_w * scale_freq>> SCHED_CAPACITY_SHIFT;so the only thing that could be improved is somehow making this multiplication go away when the arch doesn't implement the function.
But I'm not sure how to do that without #ifdef.
Maybe a little something like so then... that should make the compiler get rid of those multiplications unless the arch needs them.
yes, it removes useless multiplication when not used by an arch. It also adds a constraint on the arch side which have to define arch_scale_freq_capacity like below:
#define arch_scale_freq_capacity xxx_arch_scale_freq_capacity with xxx_arch_scale_freq_capacity an architecture specific function
If it sounds acceptable i can update the patch with your proposal ?
Vincent
--- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2484,8 +2484,6 @@ static u32 __compute_runnable_contrib(u6 return contrib + runnable_avg_yN_sum[n]; }
-unsigned long __weak arch_scale_freq_capacity(struct sched_domain *sd, int cpu);
/*
- We can represent the historical contribution to runnable average as the
- coefficients of a geometric series. To do this we sub-divide our runnable
@@ -6015,11 +6013,6 @@ static unsigned long default_scale_capac return SCHED_CAPACITY_SCALE; }
-unsigned long __weak arch_scale_freq_capacity(struct sched_domain *sd, int cpu) -{
return default_scale_capacity(sd, cpu);-}
static unsigned long default_scale_cpu_capacity(struct sched_domain *sd, int cpu) { if ((sd->flags & SD_SHARE_CPUCAPACITY) && (sd->span_weight > 1)) --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1387,7 +1387,14 @@ static inline int hrtick_enabled(struct
#ifdef CONFIG_SMP extern void sched_avg_update(struct rq *rq); -extern unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu);
+#ifndef arch_scale_freq_capacity +static __always_inline +unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu) +{
return SCHED_CAPACITY_SCALE;+} +#endif
static inline void sched_rt_avg_update(struct rq *rq, u64 rt_delta) {