Messages in this thread | | | Subject | Re: [PATCH V7 08/14] perf/x86/intel: Generic support for hardware TopDown metrics | From | "Liang, Kan" <> | Date | Tue, 28 Jul 2020 10:01:25 -0400 |
| |
On 7/28/2020 9:44 AM, peterz@infradead.org wrote: > On Tue, Jul 28, 2020 at 09:28:39AM -0400, Liang, Kan wrote: >> >> >> On 7/28/2020 9:09 AM, Peter Zijlstra wrote: >>> On Fri, Jul 24, 2020 at 03:10:52PM -0400, Liang, Kan wrote: >>> >>>> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c >>>> index 6cb079e0c9d9..010ac74afc09 100644 >>>> --- a/arch/x86/events/intel/core.c >>>> +++ b/arch/x86/events/intel/core.c >>>> @@ -2405,27 +2405,18 @@ static u64 icl_update_topdown_event(struct >>>> perf_event *event) >>>> return slots; >>>> } >>>> >>>> -static void intel_pmu_read_topdown_event(struct perf_event *event) >>>> +static void intel_pmu_read_event(struct perf_event *event) >>>> { >>>> - struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); >>>> - >>>> - /* Only need to call update_topdown_event() once for group read. */ >>>> - if ((cpuc->txn_flags & PERF_PMU_TXN_READ) && >>>> - !is_slots_event(event)) >>>> return; >>>> >>>> - perf_pmu_disable(event->pmu); >>>> - x86_pmu.update_topdown_event(event); >>>> - perf_pmu_enable(event->pmu); >>>> -} >>>> - >>>> -static void intel_pmu_read_event(struct perf_event *event) >>>> -{ >>>> if (event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD) >>>> intel_pmu_auto_reload_read(event); >>>> - else if (is_topdown_count(event) && x86_pmu.update_topdown_event) >>>> - intel_pmu_read_topdown_event(event); >>>> - else >>>> + else if (is_slots_count(event) && x86_pmu.update_topdown_event) { >>>> + perf_pmu_disable(event->pmu); >>>> + x86_pmu.update_topdown_event(event); >>>> + perf_pmu_enable(event->pmu); >>>> + } else >>>> x86_perf_event_update(event); >>>> } >>> >>> I'm a little puzzled by this; what happens if you: >>> >>> fd = sys_perf_event_open(&attr_slots); >>> fd1 = sys_perf_event_open(&attr_metric, .group_fd=fd); >>> >>> read(fd1); >>> >>> ? >>> >> >> I did a quick test. It depends on the .read_format of attr_metric. >> If PERF_FORMAT_GROUP is applied for attr_metric, perf_read_group() will be >> invoked. The value of fd1 is updated correctly. >> If the flag is not applied, 0 will be returned. > > Exactly :-), was that intentional?
Kind of, because a metric event must be in a group with the leader slots event. If a user reads (treats) the metric event as a singleton event, an invalid value should be expected.
> Because prior to this change that > would've worked just fine. > > Now, I agree it's a daft thing, because that value is pretty useless > without also having the slots value, but I feel we should be explicit in > our choices here. > > If for example, we would've had hardware provide us the raw metric > counters, instead of us having to reconstruct them, this would've been a > semi useful thing. > > So I'm tempted to leave things as it, and keep this 'working'.
I will update the perf tool document to force the PERF_FORMAT_GROUP flag for each metric events.
Thanks, Kan
| |