Peter Zijlstra <[email protected]> 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 <[email protected]> >> Reported-by: Andi Kleen <[email protected]> >> 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? Regards, -- Alex
