Re: perf_counters issue with PERF_SAMPLE_GROUP

[Peter Zijlstra]

On Tue, 2009-08-11 at 17:41 +0200, stephane eranian wrote:
> Hi,
> 
> It seems to me there is a problem with the group counter values
> when you use PERF_SAMPLE_GROUP. The counts are bogus
> for all events.
> 
> Test case is pretty simple:
>     - single group, 2 events
>     - sampling on PERF_COUNT_HW_CYCLES
>     - other event is PERF_COUNT_HW_CYCLES
>     - leader has SAMPLE_IP|SAMPLE_GROUP
>     - no inheritance
>     - single thread
>     - using sampling in one shot mode with PERF_COUNTER_IOC_REFRESH
>     - all events but leader start with disabled = 0 (i.e., enabled)
>     - sampling period is 240000000 (cycles)
> 
> Notification 1: ip=0x401300  39100608 PERF_COUNT_HW_CPU_CYCLES (12)
> Notification 2: ip=0x401300  17991616 PERF_COUNT_HW_CPU_CYCLES (12)
> Notification 3: ip=0x401300  17981248 PERF_COUNT_HW_CPU_CYCLES (12)
> Notification 4: ip=0x401300  9409478912 PERF_COUNT_HW_CPU_CYCLES (12)
> 
> I would expect the value for the 2nd event to be close to 240000000.
> But instead,
> it is going up and down. The IP, nr and id (12) fields are correct, so
> the parsing of
> the buffer is correct. This is with the latest from Linus's 2.6.31-rc5.

Could have broken somewhere along the line, the group stuff doesn't get
tested a lot, if at all.

perf used to have some support for it, not sure what the current state
is.

You seem to have forgotten to append your test.c though :-)

> Related to PERF_SAMPLE_GROUP, I believe there is some information missing.
> You need to provide the TIMING information because in the case of SAMPLE_GROUP
> you'd like to be able to scale the values of the counters you are
> collecting. And you
> need the timing at the moment, the sample was recorded not later.

Right, so something like the below, possibly complemented with having
PERF_COUNTER_IOC_RESET also reset the run-times?

---
 include/linux/perf_counter.h |    3 +++
 kernel/perf_counter.c        |   20 ++++++++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 2b36afe..44a056b 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -365,10 +365,13 @@ enum perf_event_type {
 	 * 	{ u64			period;   } && PERF_SAMPLE_PERIOD
 	 *
 	 *	{ u64			nr;
+	 *	  { u64		time_enabled; } && PERF_FORMAT_ENABLED
+	 *	  { u64		time_running; } && PERF_FORMAT_RUNNING
 	 *	  { u64 id, val; }	cnt[nr];  } && PERF_SAMPLE_GROUP
 	 *
 	 *	{ u64			nr,
 	 *	  u64			ips[nr];  } && PERF_SAMPLE_CALLCHAIN
+	 *
 	 *	{ u32			size;
 	 *	  char                  data[size];}&& PERF_SAMPLE_RAW
 	 * };
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index e26d2fc..e61e701 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -2636,6 +2636,7 @@ void perf_counter_output(struct perf_counter *counter, int nmi,
 {
 	int ret;
 	u64 sample_type = counter->attr.sample_type;
+	u64 read_format = counter->attr.read_format;
 	struct perf_output_handle handle;
 	struct perf_event_header header;
 	u64 ip;
@@ -2703,6 +2704,10 @@ void perf_counter_output(struct perf_counter *counter, int nmi,
 	if (sample_type & PERF_SAMPLE_GROUP) {
 		header.size += sizeof(u64) +
 			counter->nr_siblings * sizeof(group_entry);
+		if (read_format & PERF_FORMAT_ENABLED)
+			header.size += sizeof(u64);
+		if (read_format & PERF_FORMAT_RUNNING)
+			header.size += sizeof(u64);
 	}
 
 	if (sample_type & PERF_SAMPLE_CALLCHAIN) {
@@ -2765,9 +2770,20 @@ void perf_counter_output(struct perf_counter *counter, int nmi,
 	 */
 	if (sample_type & PERF_SAMPLE_GROUP) {
 		struct perf_counter *leader, *sub;
-		u64 nr = counter->nr_siblings;
+		u64 val;
+
+		val = counter->nr_siblings;
+		perf_output_put(&handle, val);
 
-		perf_output_put(&handle, nr);
+		if (read_format & PERF_FORMAT_ENABLED) {
+			val = counter->total_time_enabled;
+			perf_output_put(&handle, val);
+		}
+
+		if (read_format & PERF_FORMAT_RUNNING) {
+			val = counter->total_time_running;
+			perf_output_put(&handle, val);
+		}
 
 		leader = counter->group_leader;
 		list_for_each_entry(sub, &leader->sibling_list, list_entry) {


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