Messages in this thread | | | Date | Fri, 21 Jan 2011 19:06:18 +0100 | Subject | perf_events: question about __perf_event_read() | From | Stephane Eranian <> |
| |
Hi,
I think the code below still has a problem in case of a per-cpu event.
If you issue a read() on a different CPU, then you IPI to the event's cpu. By the time you get there, the event may be de-scheduled in which case you don't want to issue event->pmu_read() nor update context timings. The function has a test but it seems to be checking the per-cpu case only.
I have seen panics on P4 with this code because it goes all the way down to rdmsrl() with a bogus counter index (like -1).
Am I missing something here?
static void __perf_event_read(void *info) { struct perf_event *event = info; struct perf_event_context *ctx = event->ctx; struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
/* * If this is a task context, we need to check whether it is * the current task context of this cpu. If not it has been * scheduled out before the smp call arrived. In that case * event->count would have been updated to a recent sample * when the event was scheduled out. */ if (ctx->task && cpuctx->task_ctx != ctx) return;
raw_spin_lock(&ctx->lock); update_context_time(ctx); update_event_times(event); raw_spin_unlock(&ctx->lock);
event->pmu->read(event); }
| |