Peter Zijlstra <pet...@infradead.org> writes: > On Tue, Feb 14, 2017 at 06:17:30PM +0200, Alexander Shishkin wrote: >> This is called by pmu::add(), which checks hw.state afterwards and if it >> finds HES_STOPPED, it returns an error, which event_sched_in() captures >> and keeps the event in INACTIVE state. Should I add a comment about it? > > Egads... so what if ->add() succeeds but we then hit this on > ->stop()/->start() due to throttle or period adjust?
It will hang there with hw.state==PERF_HES_STOPPED till the next sched_out. But that will be the case anyway if VMXON kicks in while PT is running. > Now I suppose PT will never normally hit either of those, but you can do > IOC_PERIOD on it, just for giggles. True. Should we worry? > Yes, this very much needs a comment... Also, should not this then live > in ->add() in the first place? The output_stop() stuff in the mmap_close path relies on perf_aux_output_end() being in ->stop(), let me think if there's more. Regards, -- Alex
