linux-kernel - Re: [RFC PATCH 5/8] arm64: parse cpu capacity from DT

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Date:	Fri, 11 Dec 2015 10:07:35 +0000
From:	Juri Lelli <juri.lelli@....com>
To:	Dietmar Eggemann <dietmar.eggemann@....com>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	peterz@...radead.org, vincent.guittot@...aro.org,
	robh+dt@...nel.org, mark.rutland@....com, linux@....linux.org.uk,
	sudeep.holla@....com, lorenzo.pieralisi@....com,
	catalin.marinas@....com, will.deacon@....com,
	morten.rasmussen@....com, Mark Brown <broonie@...aro.org>
Subject: Re: [RFC PATCH 5/8] arm64: parse cpu capacity from DT

Hi,

On 10/12/15 14:15, Dietmar Eggemann wrote:
> On 23/11/15 14:28, Juri Lelli wrote:
> > With the introduction of cpu capacity bindings, CPU capacities can now be
> > extracted from DT. Add parsing of such information at boot time. Also,
> > store such information using per CPU variables, as we do for arm.
> > 
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: Will Deacon <will.deacon@....com>
> > Cc: Mark Brown <broonie@...aro.org>
> > Cc: Sudeep Holla <sudeep.holla@....com>
> > Signed-off-by: Juri Lelli <juri.lelli@....com>
> > ---
> >  arch/arm64/kernel/topology.c | 46 ++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 46 insertions(+)
> 
> A lot of code disappears if you get rid of capacity-scale.
> 

Some code disappears yes, but I'll have to put some other code to
normalize capacities w.r.t. the highest capacity amongst CPUs. Not
a problem, though :-).

Thanks,

- Juri

> > 
> > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> > index 694f6de..4423cc5 100644
> > --- a/arch/arm64/kernel/topology.c
> > +++ b/arch/arm64/kernel/topology.c
> > @@ -23,6 +23,45 @@
> >  #include <asm/cputype.h>
> >  #include <asm/topology.h>
> >  
> > +static DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
> > +
> > +unsigned long arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
> > +{
> > +	return per_cpu(cpu_scale, cpu);
> > +}
> > +
> > +static void set_capacity_scale(unsigned int cpu, unsigned long capacity)
> > +{
> > +	per_cpu(cpu_scale, cpu) = capacity;
> > +}
> > +
> > +static u32 capacity_scale = SCHED_CAPACITY_SCALE;
> > +
> > +static void __init parse_cpu_capacity(struct device_node *cpu_node, int cpu)
> > +{
> > +	int ret;
> > +	u32 cpu_capacity;
> > +
> > +	ret = of_property_read_u32(cpu_node,
> > +				   "capacity",
> > +				   &cpu_capacity);
> > +	if (!ret) {
> > +		u64 capacity;
> > +
> > +		/*
> > +		 * Enforce capacity <= capacity-scale.
> > +		 */
> > +		cpu_capacity = cpu_capacity <= capacity_scale ? cpu_capacity :
> > +			capacity_scale;
> > +		capacity = (cpu_capacity << SCHED_CAPACITY_SHIFT) /
> > +			capacity_scale;
> > +
> > +		set_capacity_scale(cpu, capacity);
> > +		pr_info("CPU%d: DT cpu_capacity %lu\n",
> > +			cpu, arch_scale_cpu_capacity(NULL, cpu));
> > +	}
> > +}
> > +
> >  static int __init get_cpu_for_node(struct device_node *node)
> >  {
> >  	struct device_node *cpu_node;
> > @@ -34,6 +73,7 @@ static int __init get_cpu_for_node(struct device_node *node)
> >  
> >  	for_each_possible_cpu(cpu) {
> >  		if (of_get_cpu_node(cpu, NULL) == cpu_node) {
> > +			parse_cpu_capacity(cpu_node, cpu);
> >  			of_node_put(cpu_node);
> >  			return cpu;
> >  		}
> > @@ -173,6 +213,12 @@ static int __init parse_dt_topology(void)
> >  		return 0;
> >  	}
> >  
> > +	if (!of_property_read_u32(cn, "capacity-scale", &capacity_scale))
> > +		pr_info("DT cpus capacity-scale %u\n", capacity_scale);
> > +	else
> > +		pr_debug("DT cpus capacity-scale not found: assuming %u\n",
> > +			capacity_scale);
> > +
> >  	/*
> >  	 * When topology is provided cpu-map is essentially a root
> >  	 * cluster with restricted subnodes.
> > 
> 
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