| Message ID | 1505151134-26128-1-git-send-email-anju@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | powerpc/perf: Fix for core/nest imc call trace on cpuhotplug | expand |
Anju T Sudhakar <anju@linux.vnet.ibm.com> writes: > Nest/core pmu units are enabled only when it is used. A reference count is > maintained for the events which uses the nest/core pmu units. Currently in > *_imc_counters_release function a WARN() is used for notification of any > underflow of ref count. Replace WARN() with a pr_info since it is an overkill. As discussed elsewhere this is not the right solution. If it's OK for the reference count to be negative, then we shouldn't print anything when it is. But I don't understand how it can be OK for the refcount to be negative. That means someone has a negative number of references to something? cheers
Hi mpe, On Thursday 21 September 2017 10:04 AM, Michael Ellerman wrote: > Anju T Sudhakar <anju@linux.vnet.ibm.com> writes: > >> Nest/core pmu units are enabled only when it is used. A reference count is >> maintained for the events which uses the nest/core pmu units. Currently in >> *_imc_counters_release function a WARN() is used for notification of any >> underflow of ref count. Replace WARN() with a pr_info since it is an overkill. > As discussed elsewhere this is not the right solution. > > If it's OK for the reference count to be negative, then we shouldn't > print anything when it is. > > But I don't understand how it can be OK for the refcount to be negative. > That means someone has a negative number of references to something? > > cheers > Scenario where this happens is in a stress test where perf session is started, followed by offlining of all cpus in a given core. And finally terminate the perf session. So, in cpuhotplug offline path(ppc_core_imc_cpu_offline), function set the ref->count to zero, if the current cpu which is about to offline is the last cpu in a given core and make an OPAL call to disable the engine in that core. And on perf session termination, perf->destory (core_imc_counters_release) will first decrement the ref->count for this core and based on the ref->count value an opal call is made to disable the core-imc engine. Now, since cpuhotplug path already clears the ref->count for core and disabled the engine, perf->destroy() decrementing again at event termination make it negative which in turn fires the WARN_ON. So we do prefer to remove the message as this wont happen in normal operation and the core counters are working as expected. I will send out a patch by removing the message asap. Thanks, Anju
diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c index 9ccac86..4d523d0 100644 --- a/arch/powerpc/perf/imc-pmu.c +++ b/arch/powerpc/perf/imc-pmu.c @@ -409,7 +409,7 @@ static void nest_imc_counters_release(struct perf_event *event) return; } } else if (ref->refc < 0) { - WARN(1, "nest-imc: Invalid event reference count\n"); + pr_info("nest-imc: Invalid event reference count\n"); ref->refc = 0; } mutex_unlock(&ref->lock); @@ -656,7 +656,7 @@ static void core_imc_counters_release(struct perf_event *event) return; } } else if (ref->refc < 0) { - WARN(1, "core-imc: Invalid event reference count\n"); + pr_info("core-imc: Invalid event reference count\n"); ref->refc = 0; } mutex_unlock(&ref->lock);