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 09:28:39 -0400 |
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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.
static ssize_t __perf_read(struct perf_event *event, char __user *buf, size_t count) { u64 read_format = event->attr.read_format; int ret;
/* * Return end-of-file for a read on an event that is in * error state (i.e. because it was pinned but it couldn't be * scheduled on to the CPU at some point). */ if (event->state == PERF_EVENT_STATE_ERROR) return 0;
if (count < event->read_size) return -ENOSPC;
WARN_ON_ONCE(event->ctx->parent_ctx); if (read_format & PERF_FORMAT_GROUP) ret = perf_read_group(event, read_format, buf); else ret = perf_read_one(event, read_format, buf);
return ret; }
Thanks, Kan
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