Hi Arnaldo, Kajol reflects this issue for almost two months, got no feedbacks, do you have any comments? That could be appreciated if you can look into it. Thanks a lot!
Please refer to below link: https://www.spinics.net/lists/linux-perf-users/msg11011.html Best Regards, Joakim Zhang > -----Original Message----- > From: kajoljain <[email protected]> > Sent: 2020年3月24日 16:01 > To: Joakim Zhang <[email protected]>; [email protected]; Jiri Olsa > <[email protected]>; Andi Kleen <[email protected]> > Cc: [email protected]; [email protected]; Kan Liang > <[email protected]>; Madhavan Srinivasan > <[email protected]>; Anju T Sudhakar <[email protected]>; > Ravi Bangoria <[email protected]> > Subject: [RFC] Issue in final aggregate value, in case of multiple events > present > in metric expression > > Hello All, > I want to discuss one issue raised by Joakim Zhang where he mentioned > that, we are not getting correct result in-case of multiple events present in > metric expression. > > This is one example pointed by him : > > below is the JSON file and result. > [ > { > "PublicDescription": "Calculate DDR0 bus actual utilization > which vary from DDR0 controller clock frequency", > "BriefDescription": "imx8qm: ddr0 bus actual utilization", > "MetricName": "imx8qm-ddr0-bus-util", > "MetricExpr": "( imx8_ddr0\\/read\\-cycles\\/ + > imx8_ddr0\\/write\\-cycles\\/ )", > "MetricGroup": "i.MX8QM_DDR0_BUS_UTIL" > } > ] > ./perf stat -I 1000 -M imx8qm-ddr0-bus-util > # time counts unit events > 1.000104250 16720 imx8_ddr0/read-cycles/ > # 22921.0 imx8qm-ddr0-bus-util > 1.000104250 6201 imx8_ddr0/write-cycles/ > 2.000525625 8316 imx8_ddr0/read-cycles/ > # 12785.5 imx8qm-ddr0-bus-util > 2.000525625 2738 imx8_ddr0/write-cycles/ > 3.000819125 1056 imx8_ddr0/read-cycles/ > # 4136.7 imx8qm-ddr0-bus-util > 3.000819125 303 imx8_ddr0/write-cycles/ > 4.001103750 6260 imx8_ddr0/read-cycles/ > # 9149.8 imx8qm-ddr0-bus-util > 4.001103750 2317 imx8_ddr0/write-cycles/ > 5.001392750 2084 imx8_ddr0/read-cycles/ > # 4516.0 imx8qm-ddr0-bus-util > 5.001392750 601 imx8_ddr0/write-cycles/ > > Based on given metric expression, the sum coming correct for first iteration > while for rest, we won't see same addition result. But in-case we have single > event in metric expression, we are getting correct result as expected. > > > So, I try to look into this issue and understand the flow. From my > understanding, > whenever we do calculation of metric expression we don't use exact count we > are getting. > Basically we use mean value of each metric event in the calculation of metric > expression. > > So, I take same example: > > Metric Event: imx8qm-ddr0-bus-util > MetricExpr": "( imx8_ddr0\\/read\\-cycles\\/ + imx8_ddr0\\/write\\-cycles\\/ > )" > > command#: ./perf stat -I 1000 -M imx8qm-ddr0-bus-util > > # time counts unit events > 1.000104250 16720 imx8_ddr0/read-cycles/ > # 22921.0 imx8qm-ddr0-bus-util > 1.000104250 6201 imx8_ddr0/write-cycles/ > 2.000525625 8316 imx8_ddr0/read-cycles/ > # 12785.5 imx8qm-ddr0-bus-util > 2.000525625 2738 imx8_ddr0/write-cycles/ > 3.000819125 1056 imx8_ddr0/read-cycles/ > # 4136.7 imx8qm-ddr0-bus-util > 3.000819125 303 imx8_ddr0/write-cycles/ > 4.001103750 6260 imx8_ddr0/read-cycles/ > # 9149.8 imx8qm-ddr0-bus-util > 4.001103750 2317 imx8_ddr0/write-cycles/ > 5.001392750 2084 imx8_ddr0/read-cycles/ > # 4516.0 imx8qm-ddr0-bus-util > 5.001392750 601 imx8_ddr0/write-cycles/ > > So, there is one function called 'update_stats' in file util/stat.c where we > do this > calculation and updating stats->mean value. And this mean value is what we > are actually using in our metric expression calculation. > > We call this function in each iteration where we update stats->mean and > stats->n for each event. > But one weird issue is, for very first event, stat->n is always 1 that is why > we > are getting mean same as count. > > So this the reason why for single event we get exact aggregate of metric > expression. > So doesn't matter how many events you have in your metric expression, every > time you take exact count for first one and normalized value for rest which is > weird. > > According to update_stats function: We are updating mean as: > > stats->mean += delta / stats->n where, delta = val - stats->mean. > > If we take write-cycles here. Initially mean = 0 and n = 1. > > 1st iteration: n=1, write cycle : 6201 and mean = 6201 (Final agg value: > 16720 > + 6201 = 22921) 2nd iteration: n=2, write cycles: 6201 + (2738 - 6201)/2 = > 4469.5 (Final aggr value: 8316 + 4469.5 = 12785.5) 3rd iteration: n=3, write > cycles: 4469.5 + (303 - 4469.5)/3 = 3080.6667 (Final aggr value: 1056 + > 3080.6667 = 4136.7) > > I am not sure if its expected behavior. I mean shouldn't we either take mean > value of each event or take n as 1 for each event. > > > I am thinking, Should we add an option to say whether user want exact > aggregate or > this normalize aggregate to remove the confusion? I try to find it out if we > already have one but didn't get. > Please let me know if my understanding is fine. Or something I can add to > resolve this issue. > > Thanks, > Kajol
