From mboxrd@z Thu Jan 1 00:00:00 1970 From: kajoljain Subject: Re: [PATCH v4] tools/perf/metricgroup: Fix printing event names of metric group with multiple events incase of overlapping events Date: Tue, 24 Mar 2020 12:43:32 +0530 Message-ID: <648e08fb-ffd2-16f6-005d-527ac3fee6c0@linux.ibm.com> References: <20200212054102.9259-1-kjain@linux.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Joakim Zhang , "acme@kernel.org" , Jiri Olsa , Andi Kleen Cc: "linux-kernel@vger.kernel.org" , "linux-perf-users@vger.kernel.org" , Alexander Shishkin , Kan Liang , Peter Zijlstra , Jin Yao , Madhavan Srinivasan , Anju T Sudhakar , Ravi Bangoria List-Id: linux-perf-users.vger.kernel.org On 3/20/20 12:17 PM, Joakim Zhang wrote: > > [...] >>>>> Hi Kajol, >>>>> >>>>> I am not sure if it is good to ask a question here :-) >>>>> >>>>> I encountered a perf metricgroup issue, the result is incorrect when >>>>> the >>>> metric includes more than 2 events. >>>>> >>>>> git log --oneline tools/perf/util/metricgroup.c >>>>> 3635b27cc058 perf metricgroup: Fix printing event names of metric >>>>> group with multiple events f01642e4912b perf metricgroup: Support >>>>> multiple events for metricgroup >>>>> 287f2649f791 perf metricgroup: Scale the metric result >>>>> >>>>> I did a simple test, 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/ >>>>> >>>>> You can see that only the first result is correct, could this be >>>>> reproduced at >>>> you side? >>>> >>>> Hi Joakim, >>>> Will try to look into it from my side. >>> >> >>> Thanks Kajol for your help, I look into this issue, but don't know how to fix it. >>> >>> The results are always correct if signal event used in "MetricExpr" with "-I" >> parameters, but the results are incorrect when more than one events used in >> "MetricExpr". >>> >> >> Hi Joakim, >> 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 event in the calculation of metric >> expression. >> >> So, I am taking same example you refer. >> >> 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/ >> >> If you see we have a 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 using actually 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 is the reason for single event you 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) >> >> Andi and Jiri, 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. And one more >> question, 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. > > Hi Kajol, > > Sorry, your reply was buried in a sea of emails, it comes into my eyes when I searched any feedback from you. Much thanks for your great details!!!!! > > I can quite understand what you explained. As a user, I think we always want to get the exact result according to the metric expression. > > Can you take this case as an example then send out a formal email into mailing list to reflect this weird issue, more people can participate and discuss about it. Or you need me clear up and sent out the email? > This could attract maintainers' attention. > Hi Joakim, Yes you are right, I will send separate mail on lkml. That way it will be better. Thanks, Kajol > Best Regards, > Joakim Zhang >