Messages in this thread | | | Date | Tue, 6 Jun 2017 12:27:38 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH v9 10/10] powerpc/perf: Thread imc cpuhotplug support |
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On Mon, 5 Jun 2017, Anju T Sudhakar wrote: > static void thread_imc_mem_alloc(int cpu_id) > { > - u64 ldbar_addr, ldbar_value; > int phys_id = topology_physical_package_id(cpu_id); > > per_cpu_add[cpu_id] = (u64)alloc_pages_exact_nid(phys_id, > (size_t)IMC_THREAD_COUNTER_MEM, GFP_KERNEL | __GFP_ZERO);
It took me a while to understand that per_cpu_add is an array and not a new fangled per cpu function which adds something to a per cpu variable.
So why is that storing the address as u64?
And why is this a NR_CPUS sized array instead of a regular per cpu variable?
> +} > + > +static void thread_imc_update_ldbar(unsigned int cpu_id) > +{ > + u64 ldbar_addr, ldbar_value; > + > + if (per_cpu_add[cpu_id] == 0) > + thread_imc_mem_alloc(cpu_id);
So if that allocation fails then you happily proceed. Optmistic programming, right?
> + > ldbar_addr = (u64)virt_to_phys((void *)per_cpu_add[cpu_id]);
Ah, it's stored as u64 because you have to convert it back to a void pointer at the place where it is actually used. Interesting approach.
> ldbar_value = (ldbar_addr & (u64)THREAD_IMC_LDBAR_MASK) | > - (u64)THREAD_IMC_ENABLE; > + (u64)THREAD_IMC_ENABLE; > mtspr(SPRN_LDBAR, ldbar_value); > } > > @@ -442,6 +450,26 @@ static void core_imc_change_cpu_context(int old_cpu, int new_cpu) > perf_pmu_migrate_context(&core_imc_pmu->pmu, old_cpu, new_cpu); > } > > +static int ppc_thread_imc_cpu_online(unsigned int cpu) > +{ > + thread_imc_update_ldbar(cpu); > + return 0; > +} > + > +static int ppc_thread_imc_cpu_offline(unsigned int cpu) > +{ > + mtspr(SPRN_LDBAR, 0); > + return 0; > +} > + > +void thread_imc_cpu_init(void) > +{ > + cpuhp_setup_state(CPUHP_AP_PERF_POWERPC_THREAD_IMC_ONLINE, > + "perf/powerpc/imc_thread:online", > + ppc_thread_imc_cpu_online, > + ppc_thread_imc_cpu_offline); > +} > + > static int ppc_core_imc_cpu_online(unsigned int cpu) > { > const struct cpumask *l_cpumask; > @@ -953,6 +981,9 @@ int __init init_imc_pmu(struct imc_events *events, int idx, > if (ret) > return ret; > break; > + case IMC_DOMAIN_THREAD: > + thread_imc_cpu_init(); > + break; > default: > return -1; /* Unknown domain */ > }
Just a general observation. If anything in init_imc_pmu() fails, then all the hotplug callbacks are staying registered, at least I haven't seen anything undoing it.
Thanks,
tglx
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