Re: [RFC PATCH 06/10] ARM: sched: Use device-tree to provide fast/slow CPU list for HMP

["Jon Medhurst (Tixy)" <tixy@linaro.org>]

On Wed, 2012-10-10 at 12:04 +0100, Morten Rasmussen wrote:
> Hi Tixy,
> 
> Could you have a look at my code stealing patch below? Since it is
> basically a trimmed version of one of your patches I would prefer to
> put you as author and have your SOB on it. What is your opinion?

Yes, I can agree with that opinion, (and my employer likes to count
their patch totals ;-) so please feel free to add: 

From: Jon Medhurst <tixy@linaro.org>
Signed-off-by: Jon Medhurst <tixy@linaro.org>

Thanks

-- 
Tixy


> Thanks,
> Morten
> 
> On Fri, Sep 21, 2012 at 07:32:21PM +0100, Morten Rasmussen wrote:
> > From: Morten Rasmussen <morten.rasmussen@arm.com>
> > 
> > We can't rely on Kconfig options to set the fast and slow CPU lists for
> > HMP scheduling if we want a single kernel binary to support multiple
> > devices with different CPU topology. E.g. TC2 (ARM's Test-Chip-2
> > big.LITTLE system), Fast Models, or even non big.LITTLE devices.
> > 
> > This patch adds the function arch_get_fast_and_slow_cpus() to generate
> > the lists at run-time by parsing the CPU nodes in device-tree; it
> > assumes slow cores are A7s and everything else is fast. The function
> > still supports the old Kconfig options as this is useful for testing the
> > HMP scheduler on devices without big.LITTLE.
> > 
> > This patch is reuse of a patch by Jon Medhurst <tixy@linaro.org> with a
> > few bits left out.
> > 
> > Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
> > ---
> >  arch/arm/Kconfig           |    4 ++-
> >  arch/arm/kernel/topology.c |   69 ++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 72 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index cb80846..f1271bc 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -1588,13 +1588,15 @@ config HMP_FAST_CPU_MASK
> >  	string "HMP scheduler fast CPU mask"
> >  	depends on SCHED_HMP
> >  	help
> > -          Specify the cpuids of the fast CPUs in the system as a list string,
> > +          Leave empty to use device tree information.
> > +	  Specify the cpuids of the fast CPUs in the system as a list string,
> >  	  e.g. cpuid 0+1 should be specified as 0-1.
> >  
> >  config HMP_SLOW_CPU_MASK
> >  	string "HMP scheduler slow CPU mask"
> >  	depends on SCHED_HMP
> >  	help
> > +	  Leave empty to use device tree information.
> >  	  Specify the cpuids of the slow CPUs in the system as a list string,
> >  	  e.g. cpuid 0+1 should be specified as 0-1.
> >  
> > diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
> > index 26c12c6..7682e12 100644
> > --- a/arch/arm/kernel/topology.c
> > +++ b/arch/arm/kernel/topology.c
> > @@ -317,6 +317,75 @@ void store_cpu_topology(unsigned int cpuid)
> >  		cpu_topology[cpuid].socket_id, mpidr);
> >  }
> >  
> > +
> > +#ifdef CONFIG_SCHED_HMP
> > +
> > +static const char * const little_cores[] = {
> > +	"arm,cortex-a7",
> > +	NULL,
> > +};
> > +
> > +static bool is_little_cpu(struct device_node *cn)
> > +{
> > +	const char * const *lc;
> > +	for (lc = little_cores; *lc; lc++)
> > +		if (of_device_is_compatible(cn, *lc))
> > +			return true;
> > +	return false;
> > +}
> > +
> > +void __init arch_get_fast_and_slow_cpus(struct cpumask *fast,
> > +					struct cpumask *slow)
> > +{
> > +	struct device_node *cn = NULL;
> > +	int cpu = 0;
> > +
> > +	cpumask_clear(fast);
> > +	cpumask_clear(slow);
> > +
> > +	/*
> > +	 * Use the config options if they are given. This helps testing
> > +	 * HMP scheduling on systems without a big.LITTLE architecture.
> > +	 */
> > +	if (strlen(CONFIG_HMP_FAST_CPU_MASK) && strlen(CONFIG_HMP_SLOW_CPU_MASK)) {
> > +		if (cpulist_parse(CONFIG_HMP_FAST_CPU_MASK, fast))
> > +			WARN(1, "Failed to parse HMP fast cpu mask!\n");
> > +		if (cpulist_parse(CONFIG_HMP_SLOW_CPU_MASK, slow))
> > +			WARN(1, "Failed to parse HMP slow cpu mask!\n");
> > +		return;
> > +	}
> > +
> > +	/*
> > +	 * Else, parse device tree for little cores.
> > +	 */
> > +	while ((cn = of_find_node_by_type(cn, "cpu"))) {
> > +
> > +		if (cpu >= num_possible_cpus())
> > +			break;
> > +
> > +		if (is_little_cpu(cn))
> > +			cpumask_set_cpu(cpu, slow);
> > +		else
> > +			cpumask_set_cpu(cpu, fast);
> > +
> > +		cpu++;
> > +	}
> > +
> > +	if (!cpumask_empty(fast) && !cpumask_empty(slow))
> > +		return;
> > +
> > +	/*
> > +	 * We didn't find both big and little cores so let's call all cores
> > +	 * fast as this will keep the system running, with all cores being
> > +	 * treated equal.
> > +	 */
> > +	cpumask_setall(fast);
> > +	cpumask_clear(slow);
> > +}
> > +
> > +#endif /* CONFIG_SCHED_HMP */
> > +
> > +
> >  /*
> >   * init_cpu_topology is called at boot when only one cpu is running
> >   * which prevent simultaneous write access to cpu_topology array
> > -- 
> > 1.7.9.5
> > 
>