On Fri, Aug 05, 2016 at 10:22:08AM -0700, Brendan Gregg wrote: > (Normally I'd use I$ miss overflow, but none of our Linux systems have > PMCs: cloud.)
I think I had better not comment on that ;-) > >> > The perf:perf_hrtimer probe point is also reading state mid-way > >> > through a function, so it's not quite as simple as wrapping the > >> > function pointer. I do like that idea, though, but for things like > >> > struct file_operations. > > > > So what additional state to you need? > > I was pulling in regs after get_irq_regs(), struct perf_event *event > after it's populated. Not that hard to duplicate. Just noting it > didn't map directly to the function entry. Right, both of which are available to the overflow handler. > I wanted perf_event just for event->ctx->task->pid, so that a BPF > program can differentiate between it's samples and other concurrent > sessions. > > (I was thinking of changing my patch to expose pid_t instead of > perf_event, since I was noticing it didn't add many instructions.) Slightly confused, event->ctx->task == current, no? We flip that pointer when we flip the contexts. At which point, it should be the same as SAMPLE_TID. !? > [...] > >> instead of adding a tracepoint to perf_swevent_hrtimer we can replace > >> overflow_handler for that particular event with some form of bpf wrapper. > >> (probably new bpf program type). Then not only periodic events > >> will be triggering bpf prog, but pmu events as well. > > > > Exactly. > > Although the timer use case is a bit different, and is via > hwc->hrtimer.function = perf_swevent_hrtimer. Still not entirely sure why you could not hook into event->overflow_handler.
