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

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Date:   Tue, 28 Mar 2017 10:11:51 +0530
From:   Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
To:     ego@...ux.vnet.ibm.com
Cc:     mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org,
        Hemant Kumar <hemant@...ux.vnet.ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Anton Blanchard <anton@...ba.org>,
        Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
        Michael Neuling <mikey@...ling.org>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        Daniel Axtens <dja@...ens.net>,
        Stephane Eranian <eranian@...gle.com>,
        Anju T Sudhakar <anju@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5 08/13] powerpc/perf: PMU functions for Core IMC and
 hotplugging



On Thursday 23 March 2017 06:39 PM, Gautham R Shenoy wrote:
> 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 ?

Yes. This makes sense. Let me look at this.

Thanks for review
Maddy

>
> 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.