Re: [PATCH v5 08/13] powerpc/perf: PMU functions for Core IMC and hotplugging

[Gautham R Shenoy <ego@linux.vnet.ibm.com>]

Hi Maddy, Hemant, Anju,

On Thu, Mar 16, 2017 at 01:05:02PM +0530, Madhavan Srinivasan wrote:

[..snip..]

> +
> +static void core_imc_change_cpu_context(int old_cpu, int new_cpu)
> +{
> +	if (!core_imc_pmu)
> +		return;
> +	perf_pmu_migrate_context(&core_imc_pmu->pmu, old_cpu, new_cpu);
> +}
> +
> +
> +static int ppc_core_imc_cpu_online(unsigned int cpu)
> +{
> +	int ret;
> +
> +	/* If a cpu for this core is already set, then, don't do anything */
> +	ret = cpumask_any_and(&core_imc_cpumask,
> +				 cpu_sibling_mask(cpu));
> +	if (ret < nr_cpu_ids)
> +		return 0;
> +
> +	/* Else, set the cpu in the mask, and change the context */
> +	cpumask_set_cpu(cpu, &core_imc_cpumask);
> +	core_imc_change_cpu_context(-1, cpu);

So, in the core case, we are ok as long as any cpu in the core is
present in the imc_cpumask. It need not have to be the smallest online
cpu in the core.

Can the same logic be applied to the earlier nest case ?

We can have a single function for cpu_offline and cpu_online which
implements these checks and sets the cpu bit if required.

ppc_entity_imc_cpu_offline(unsigned int cpu, cpumask_t
			   entity_imc_mask,
			   entity_imc_change_cpu_context_fn)
{
	.
	.
	.
	
}


static ppc_nest_imc_cpu_offline(unsigned int cpu)
{
	return ppc_entity_imc_cpu_offline(cpu, nest_imc_mask,
					  nest_imc_change_cpu_context);
}

And similar ones for core imc and thread imc.

Does this sound reasonable ?

> +	return 0;
> +}
> +
> +static int ppc_core_imc_cpu_offline(unsigned int cpu)
> +{
> +	int target;
> +	unsigned int ncpu;
> +
> +	/*
> +	 * clear this cpu out of the mask, if not present in the mask,
> +	 * don't bother doing anything.
> +	 */
> +	if (!cpumask_test_and_clear_cpu(cpu, &core_imc_cpumask))
> +		return 0;
> +
> +	/* Find any online cpu in that core except the current "cpu" */
> +	ncpu = cpumask_any_but(cpu_sibling_mask(cpu), cpu);
> +
> +	if (ncpu < nr_cpu_ids) {
> +		target = ncpu;
> +		cpumask_set_cpu(target, &core_imc_cpumask);
> +	} else
> +		target = -1;
> +
> +	/* migrate the context */
> +	core_imc_change_cpu_context(cpu, target);
> +
> +	return 0;
> +}
> +

--
Thanks and Regards
gautham.