Hello My student actually noticed this before I did, I was hoping it was some sort of error in her data.
Anyway all perf_event functionality (especially reads) has become about 20x slower, at least on Intel machines (haswell and skylake are the only ones I've tested) sometime between 4.9 and 4.11-rc For example, in the PAPI tests: 4.11-rc2 Total cost for PAPI_read (2 counters) over 1000000 iterations min cycles : 15192 max cycles : 3887735 mean cycles : 15662.057418 std deviation: 19079.398693 4.9 Total cost for PAPI_read (2 counters) over 1000000 iterations min cycles : 864 max cycles : 78459 mean cycles : 908.010315 std deviation: 144.875697 The perf_event_test validation tests are also showing this, even when using rdpmc() rather than read. Is there a likely change that might have caused this? Hoping to avoid bisecting it as that will kill the rest of the week probably. Vince
