From: Peter Zijlstra peterz@infradead.org
[ Upstream commit ba5213ae6b88fb170c4771fef6553f759c7d8cdd ]
Andi was asking about PERF_FORMAT_GROUP vs inherited events, which led to the discovery of a bug from commit:
3dab77fb1bf8 ("perf: Rework/fix the whole read vs group stuff")
- PERF_SAMPLE_GROUP = 1U << 4, + PERF_SAMPLE_READ = 1U << 4,
- if (attr->inherit && (attr->sample_type & PERF_SAMPLE_GROUP)) + if (attr->inherit && (attr->read_format & PERF_FORMAT_GROUP))
is a clear fail :/
While this changes user visible behaviour; it was previously possible to create an inherited event with PERF_SAMPLE_READ; this is deemed acceptible because its results were always incorrect.
Reported-by: Andi Kleen ak@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Arnaldo Carvalho de Melo acme@kernel.org Cc: Jiri Olsa jolsa@kernel.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Stephane Eranian eranian@google.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Vince Weaver vince@deater.net Fixes: 3dab77fb1bf8 ("perf: Rework/fix the whole read vs group stuff") Link: http://lkml.kernel.org/r/20170530094512.dy2nljns2uq7qa3j@hirez.programming.k... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- kernel/events/core.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index de3303aab7d6..9eb7710914fb 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4861,9 +4861,6 @@ static void perf_output_read_one(struct perf_output_handle *handle, __output_copy(handle, values, n * sizeof(u64)); }
-/* - * XXX PERF_FORMAT_GROUP vs inherited events seems difficult. - */ static void perf_output_read_group(struct perf_output_handle *handle, struct perf_event *event, u64 enabled, u64 running) @@ -4908,6 +4905,13 @@ static void perf_output_read_group(struct perf_output_handle *handle, #define PERF_FORMAT_TOTAL_TIMES (PERF_FORMAT_TOTAL_TIME_ENABLED|\ PERF_FORMAT_TOTAL_TIME_RUNNING)
+/* + * XXX PERF_SAMPLE_READ vs inherited events seems difficult. + * + * The problem is that its both hard and excessively expensive to iterate the + * child list, not to mention that its impossible to IPI the children running + * on another CPU, from interrupt/NMI context. + */ static void perf_output_read(struct perf_output_handle *handle, struct perf_event *event) { @@ -7194,9 +7198,10 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu, local64_set(&hwc->period_left, hwc->sample_period);
/* - * we currently do not support PERF_FORMAT_GROUP on inherited events + * We currently do not support PERF_SAMPLE_READ on inherited events. + * See perf_output_read(). */ - if (attr->inherit && (attr->read_format & PERF_FORMAT_GROUP)) + if (attr->inherit && (attr->sample_type & PERF_SAMPLE_READ)) goto err_ns;
pmu = perf_init_event(event);