Messages in this thread | | | From | Joakim Zhang <> | Subject | RE: [RFC] Issue in final aggregate value, in case of multiple events present in metric expression | Date | Mon, 11 May 2020 02:05:05 +0000 |
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> -----Original Message----- > From: Jin, Yao <yao.jin@linux.intel.com> > Sent: 2020年5月11日 9:12 > To: kajoljain <kjain@linux.ibm.com>; Joakim Zhang > <qiangqing.zhang@nxp.com>; acme@kernel.org; Jiri Olsa <jolsa@kernel.org>; > Andi Kleen <ak@linux.intel.com> > Cc: linux-kernel@vger.kernel.org; linux-perf-users@vger.kernel.org; Kan Liang > <kan.liang@linux.intel.com>; Madhavan Srinivasan > <maddy@linux.vnet.ibm.com>; Anju T Sudhakar <anju@linux.vnet.ibm.com>; > Ravi Bangoria <ravi.bangoria@linux.ibm.com> > Subject: Re: [RFC] Issue in final aggregate value, in case of multiple events > present in metric expression > > Hi Kajol, > > On 3/24/2020 4:00 PM, kajoljain wrote: > > 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 > > > > Since you use the interval mode, can this commit fix the issue? > > https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Flore.kern > el.org%2Flkml%2F20200420145417.6864-1-yao.jin%40linux.intel.com&dat > a=02%7C01%7Cqiangqing.zhang%40nxp.com%7Cb249ba9cac594c57208c08d7 > f5485feb%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637247563 > 504900211&sdata=6eyWI915sfoZsOg9XsdaaBHaEV1wdwI26ikKxHFT4a8 > %3D&reserved=0
Hi Andi, Jin Yao
Patch can fix this issue, thanks.
Best Regards, Joakim Zhang > Thanks > Jin Yao
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