Messages in this thread | | | Date | Thu, 14 Nov 2013 21:50:49 +0100 | Subject | [BUG] perf stat: explicit grouping yields unexpected results | From | Stephane Eranian <> |
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Jiri,
I was trying the grouping support in perf stat and I was surprised to see that if I create a group that is too big to be scheduled, and where only N out of P events can fit, perf stat still yields counts for the N events. I was expecting 0 counts or <not supported>.
The kernel semantic is to schedule all the events in a group or none. Perf does something different and this is confusing. If you use explicit grouping then I think you want to group to fail if not all the events can be scheduled:
On an IvyBridge: $ perf stat --g -e '{cycles,instructions,branches,branches,branches,branches,branches}' noploop 1 3 229 417 079 cycles 3 223 919 023 instructions # 1,00 insns per cycle 3 220 868 098 branches 3 220 868 098 branches 3 220 868 098 branches 3 220 868 098 branches <not supported> branches
I think it should be: <not supported> for all events.
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