Messages in this thread | | | Date | Tue, 14 Feb 2017 17:27:02 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict with VMX |
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On Tue, Feb 14, 2017 at 06:17:30PM +0200, Alexander Shishkin wrote: > Peter Zijlstra <peterz@infradead.org> writes: > > > On Tue, Feb 14, 2017 at 03:24:15PM +0200, Alexander Shishkin wrote: > >> At the moment, if VMX operation prevents PT tracing, the PMU will > >> silently return success to the event scheduling code, which will > >> track its 'on' time, etc. Instead, report failure so that perf > >> core knows this event is not actually on. > >> > >> Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> > >> Reported-by: Andi Kleen <ak@linux.intel.com> > >> Fixes: 1c5ac21a0e ("perf/x86/intel/pt: Don't die on VMXON") > >> --- > >> arch/x86/events/intel/pt.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c > >> index d92a60ef08..9372fa4549 100644 > >> --- a/arch/x86/events/intel/pt.c > >> +++ b/arch/x86/events/intel/pt.c > >> @@ -1335,7 +1335,7 @@ static void pt_event_start(struct perf_event *event, int mode) > >> struct pt_buffer *buf; > >> > >> if (READ_ONCE(pt->vmx_on)) > >> - return; > >> + goto fail_stop; > >> > >> buf = perf_aux_output_begin(&pt->handle, event); > >> if (!buf) > > > > I'm not getting it; how does this matter to the time tracking in > > event_sched_in() / event_sched_out() ? > > > > That looks at event->state == PERF_EVENT_STATE* > > > > This goto affects event->hw.state == PERF_HES_ > > > > The core assumes ->start() will _NOT_ fail. > > 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?
Now I suppose PT will never normally hit either of those, but you can do IOC_PERIOD on it, just for giggles.
Yes, this very much needs a comment... Also, should not this then live in ->add() in the first place?
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