Messages in this thread Patch in this message | | | Subject | Re: [PATCH v11 07/10] powerpc/perf: PMU functions for Core IMC and hotplugging | From | Madhavan Srinivasan <> | Date | Thu, 29 Jun 2017 14:44:19 +0530 |
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On Thursday 29 June 2017 01:11 AM, Thomas Gleixner wrote: > On Thu, 29 Jun 2017, Anju T Sudhakar wrote: >> +static void cleanup_all_core_imc_memory(struct imc_pmu *pmu_ptr) >> +{ >> + struct imc_mem_info *ptr; >> + >> + for (ptr = pmu_ptr->mem_info; ptr; ptr++) { >> + if (ptr->vbase[0]) >> + free_pages((u64)ptr->vbase[0], 0); >> + } > This loop is broken beyond repair. If pmu_ptr->mem_info is not NULL, then > ptr will happily increment to the point where it wraps around to > NULL. Oh well. > >> + kfree(pmu_ptr->mem_info); >> +bool is_core_imc_mem_inited(int cpu) > This function is global because? > >> +{ >> + struct imc_mem_info *mem_info; >> + int core_id = (cpu / threads_per_core); >> + >> + mem_info = &core_imc_pmu->mem_info[core_id]; >> + if ((mem_info->id == core_id) && (mem_info->vbase[0] != NULL)) >> + return true; >> + >> + return false; >> +} >> + >> +/* >> + * imc_mem_init : Function to support memory allocation for core imc. >> + */ >> +static int imc_mem_init(struct imc_pmu *pmu_ptr) >> +{ > The function placement is horrible. This function belongs to the pmu init > stuff and wants to be placed there and not five pages away in the middle of > unrelated functions. > >> + int nr_cores; >> + >> + if (pmu_ptr->imc_counter_mmaped) >> + return 0; >> + nr_cores = num_present_cpus() / threads_per_core; >> + pmu_ptr->mem_info = kzalloc((sizeof(struct imc_mem_info) * nr_cores), GFP_KERNEL); >> + if (!pmu_ptr->mem_info) >> + return -ENOMEM; >> + return 0; >> +} >> +static int core_imc_event_init(struct perf_event *event) >> +{ >> + int core_id, rc; >> + u64 config = event->attr.config; >> + struct imc_mem_info *pcmi; >> + struct imc_pmu *pmu; >> + >> + if (event->attr.type != event->pmu->type) >> + return -ENOENT; >> + >> + /* Sampling not supported */ >> + if (event->hw.sample_period) >> + return -EINVAL; >> + >> + /* unsupported modes and filters */ >> + if (event->attr.exclude_user || >> + event->attr.exclude_kernel || >> + event->attr.exclude_hv || >> + event->attr.exclude_idle || >> + event->attr.exclude_host || >> + event->attr.exclude_guest) >> + return -EINVAL; >> + >> + if (event->cpu < 0) >> + return -EINVAL; >> + >> + event->hw.idx = -1; >> + pmu = imc_event_to_pmu(event); >> + >> + /* Sanity check for config (event offset and rvalue) */ >> + if (((config & IMC_EVENT_OFFSET_MASK) > pmu->counter_mem_size) || >> + ((config & IMC_EVENT_RVALUE_MASK) != 0)) >> + return -EINVAL; >> + >> + if (!is_core_imc_mem_inited(event->cpu)) >> + return -ENODEV; >> + >> + core_id = event->cpu / threads_per_core; >> + pcmi = &pmu->mem_info[core_id]; >> + if ((pcmi->id != core_id) || (!pcmi->vbase[0])) >> + return -ENODEV; >> + >> + event->hw.event_base = (u64)pcmi->vbase[0] + (config & IMC_EVENT_OFFSET_MASK); >> + /* >> + * Core pmu units are enabled only when it is used. >> + * See if this is triggered for the first time. >> + * If yes, take the mutex lock and enable the core counters. >> + * If not, just increment the count in core_events. >> + */ >> + if (atomic_inc_return(&core_events[core_id]) == 1) { >> + mutex_lock(&imc_core_reserve); >> + rc = opal_imc_counters_start(OPAL_IMC_COUNTERS_CORE, >> + get_hard_smp_processor_id(event->cpu)); >> + mutex_unlock(&imc_core_reserve);
Idea is to handle multiple event session for a given core and yes, my bad, current implementation is racy/broken. But an alternate approach is to have a per-core mutex and per-core ref count to handle this.
event_init path: per-core mutex lock if ( per-core[refcount] == 0) { rc = opal call to start the engine; if (rc on failure) { per-core mutex unlock; log error info; return error; } } increment the per-core[refcount]; per-core mutex unlock;
event_destroy path: per-core mutex lock decrement the per-core[refcount]; if ( per-core[refcount] == 0) { rc = opal call to stop the engine; if (rc on failure) { per-core mutex unlock; log the failure; return error; } } else if ( per-core[refcount] < 0) { WARN() per-core[refcount] = 0; } per-core mutext unlock;
Kindly let me know your comment for this.
Maddy
> That machinery here is racy as hell in several aspects. > > CPU0 CPU1 > > atomic_inc_ret(core_events[0]) -> 1 > > preemption() > atomic_inc_ret(core_events[0]) -> 2 > return 0; > > Uses the event, without counters > being started until the preempted > task comes on the CPU again. > > Here is another one: > > CPU0 CPU1 > > atomic_dec_ret(core_events[0]) -> 0 > atomic_inc_ret(core_events[1] -> 1 > mutex_lock(); > mutex_lock() start counter(); > mutex_unlock() > > stop_counter(); > mutex_unlock(); > Yay, another stale event! > > Brilliant stuff that, or maybe not so much. > >> + if (rc) { >> + atomic_dec_return(&core_events[core_id]); > What's the point of using atomic_dec_return here if you ignore the return > value? Not that it matters much as the whole logic is crap anyway. > >> + pr_err("IMC: Unable to start the counters for core %d\n", core_id); >> + return -ENODEV; >> + } >> + } >> @@ -410,22 +658,38 @@ int init_imc_pmu(struct imc_events *events, int idx, >> struct imc_pmu *pmu_ptr) >> { >> int ret = -ENODEV; >> + > Sure ret needs to stay initialized, just in case imc_mem_init() does not > return anything magically, right? > >> + ret = imc_mem_init(pmu_ptr); >> + if (ret) >> + goto err_free; >> /* Add cpumask and register for hotplug notification */ >> - if (atomic_inc_return(&nest_pmus) == 1) { >> - /* >> - * Nest imc pmu need only one cpu per chip, we initialize the >> - * cpumask for the first nest imc pmu and use the same for the rest. >> - * To handle the cpuhotplug callback unregister, we track >> - * the number of nest pmus registers in "nest_pmus". >> - * "nest_imc_cpumask_initialized" is set to zero during cpuhotplug >> - * callback unregister. >> - */ >> - ret = nest_pmu_cpumask_init(); >> + switch (pmu_ptr->domain) { >> + case IMC_DOMAIN_NEST: >> + if (atomic_inc_return(&nest_pmus) == 1) { >> + /* >> + * Nest imc pmu need only one cpu per chip, we initialize >> + * the cpumask for the first nest imc pmu and use the >> + * same for the rest. >> + * To handle the cpuhotplug callback unregister, we track >> + * the number of nest pmus registers in "nest_pmus". >> + * "nest_imc_cpumask_initialized" is set to zero during >> + * cpuhotplug callback unregister. >> + */ >> + ret = nest_pmu_cpumask_init(); >> + if (ret) >> + goto err_free; >> + mutex_lock(&imc_nest_inited_reserve); >> + nest_imc_cpumask_initialized = 1; >> + mutex_unlock(&imc_nest_inited_reserve); >> + } >> + break; >> + case IMC_DOMAIN_CORE: >> + ret = core_imc_pmu_cpumask_init(); >> if (ret) >> - goto err_free; >> - mutex_lock(&imc_nest_inited_reserve); >> - nest_imc_cpumask_initialized = 1; >> - mutex_unlock(&imc_nest_inited_reserve); >> + return ret; > Oh, so now you replaced the goto with ret. What is actually taking care of > the cleanup if that fails? > >> + break; >> + default: >> + return -1; /* Unknown domain */ >> } >> ret = update_events_in_group(events, idx, pmu_ptr); >> if (ret) >> @@ -459,5 +723,10 @@ int init_imc_pmu(struct imc_events *events, int idx, >> mutex_unlock(&imc_nest_inited_reserve); >> } >> } >> + /* For core_imc, we have allocated memory, we need to free it */ >> + if (pmu_ptr->domain == IMC_DOMAIN_CORE) { >> + cleanup_all_core_imc_memory(pmu_ptr); >> + cpuhp_remove_state(CPUHP_AP_PERF_POWERPC_CORE_IMC_ONLINE); > Cute. You cleanuo the memory stuff and then you let the hotplug core invoke > the offline callbacks which then deal with freed memory. > > Thanks, > > tglx >
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