Re: [PATCH 0/2] perf: add sort by inclusive time functionality (v2)

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On 3/8/12 7:31 AM, Frederic Weisbecker wrote:
On Thu, Mar 08, 2012 at 08:29:01AM +0100, Ingo Molnar wrote:

* Arun Sharma<asharma@xxxxxx>  wrote:

This patch series refactors existing code a bit and adds sort by
inclusive time (time spent in the function + callees).

Sample command lines:

# perf record -ag -- sleep 1
# perf report -g graph,0.5,callee -n -s inclusive

So I tried this out with:

   $ taskset 1 perf record -g git gc

and got entries above 100% (in the TUI):

   $ perf report -g graph,0.5,callee -n -s inclusive

  +  321.11%        5628  [.] 0x392b609269
  +  142.27%        3774  [.] create_delta
  +  78.86%        1248  [.] lookup_object
  +  40.54%        1348  [k] system_call_fastpath

Is that expected?

Yes - this is the "known bug" I noted in the cover letter

The second column (samples) is still accurate and could be used for the analysis.

I think this happens because of this:

-               hists->stats.total_period += h->period;
+               if (!h->inclusive)
+                       hists->stats.total_period += h->period;

Which I'm not sure why it is needed btw.

Suppose the file had 1000 samples each with a period of 1e6 events. total_period would be 1e9 without -s inclusive. Further, let's say the callchains had an average length of 10.

Now, after adding extra entries to the histogram, total_period would be 1e10, which screws up the percentages. I'd like to differentiate between the hist entries that were in the event stream vs the ones added for inclusive time computation. Desired end result: the total_period remains unchanged at 1e9.

This is done via:

+		if (i != 0)
+			he->inclusive = 1;
+		else
+			orig_he = he;

Either (i != 0) is not a good enough test, or the inclusive bit is not getting propagated properly after histogram collapsing/resorting. This is the part I need to better understand and debug.

I tried to explain this problem in my first RFC message as well:

The problem Ingo is running into (and I've reproduced it on my end as well) is that total_period is smaller than without -s inclusive i.e. h->inclusive is 1 when it shouldn't be.

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