Messages in this thread | | | Date | Tue, 24 Mar 2015 09:41:18 +0000 | From | Morten Rasmussen <> | Subject | Re: [RFCv3 PATCH 14/48] arm: Frequency invariant scheduler load-tracking support |
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On Mon, Mar 23, 2015 at 01:39:44PM +0000, Peter Zijlstra wrote: > On Wed, Feb 04, 2015 at 06:30:51PM +0000, Morten Rasmussen wrote: > > +/* cpufreq callback function setting current cpu frequency */ > > +void arch_scale_set_curr_freq(int cpu, unsigned long freq) > > +{ > > + atomic_long_set(&per_cpu(cpu_curr_freq, cpu), freq); > > +} > > + > > +/* cpufreq callback function setting max cpu frequency */ > > +void arch_scale_set_max_freq(int cpu, unsigned long freq) > > +{ > > + atomic_long_set(&per_cpu(cpu_max_freq, cpu), freq); > > +} > > + > > +unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu) > > +{ > > + unsigned long curr = atomic_long_read(&per_cpu(cpu_curr_freq, cpu)); > > + unsigned long max = atomic_long_read(&per_cpu(cpu_max_freq, cpu)); > > + > > + if (!curr || !max) > > + return SCHED_CAPACITY_SCALE; > > + > > + return (curr * SCHED_CAPACITY_SCALE) / max; > > +} > > so I've no idea how many cycles an (integer) division takes on ARM; but > doesn't it make sense to do this division (once) in > arch_scale_set_curr_freq() instead of every time we need the result?
It does. In fact I have already prepared that fix for v4. Integer division is expensive ARM and we call this function a lot.
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