Messages in this thread | | | Date | Tue, 9 Apr 2024 14:18:19 -0400 | Subject | Re: [PATCH 3/3] perf report: Add weight[123] output fields | From | "Liang, Kan" <> |
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On 2024-04-09 12:53 p.m., Namhyung Kim wrote: > Hi Kan, > > On Tue, Apr 9, 2024 at 9:37 AM Liang, Kan <kan.liang@linux.intel.com> wrote: >> >> >> >> On 2024-04-08 8:06 p.m., Namhyung Kim wrote: >>> Add weight1, weight2 and weight3 fields to -F/--fields and their aliases >>> like 'ins_lat', 'p_stage_cyc' and 'retire_lat'. Note that they are in >>> the sort keys too but the difference is that output fields will sum up >>> the weight values and display the average. >>> >>> In the sort key, users can see the distribution of weight value and I >>> think it's confusing we have local vs. global weight for the same weight. >>> >>> For example, I experiment with mem-loads events to get the weights. On >>> my laptop, it seems only weight1 field is supported. >>> >>> $ perf mem record -- perf test -w noploop >>> >>> Let's look at the noploop function only. It has 7 samples. >>> >>> $ perf script -F event,ip,sym,weight | grep noploop >>> # event weight ip sym >>> cpu/mem-loads,ldlat=30/P: 43 55b3c122bffc noploop >>> cpu/mem-loads,ldlat=30/P: 48 55b3c122bffc noploop >>> cpu/mem-loads,ldlat=30/P: 38 55b3c122bffc noploop <--- same weight >>> cpu/mem-loads,ldlat=30/P: 38 55b3c122bffc noploop <--- same weight >>> cpu/mem-loads,ldlat=30/P: 59 55b3c122bffc noploop >>> cpu/mem-loads,ldlat=30/P: 33 55b3c122bffc noploop >>> cpu/mem-loads,ldlat=30/P: 38 55b3c122bffc noploop <--- same weight >>> >>> When you use the 'weight' sort key, it'd show entries with a separate >>> weight value separately. Also note that the first entry has 3 samples >>> with weight value 38, so they are displayed together and the weight >>> value is the sum of 3 samples (114 = 38 * 3). >>> >>> $ perf report -n -s +weight | grep -e Weight -e noploop >>> # Overhead Samples Command Shared Object Symbol Weight >>> 0.53% 3 perf perf [.] noploop 114 >>> 0.18% 1 perf perf [.] noploop 59 >>> 0.18% 1 perf perf [.] noploop 48 >>> 0.18% 1 perf perf [.] noploop 43 >>> 0.18% 1 perf perf [.] noploop 33 >>> >>> If you use 'local_weight' sort key, you can see the actualy weight. >>> >>> $ perf report -n -s +local_weight | grep -e Weight -e noploop >>> # Overhead Samples Command Shared Object Symbol Local Weight >>> 0.53% 3 perf perf [.] noploop 38 >>> 0.18% 1 perf perf [.] noploop 59 >>> 0.18% 1 perf perf [.] noploop 48 >>> 0.18% 1 perf perf [.] noploop 43 >>> 0.18% 1 perf perf [.] noploop 33 >>> >>> But when you use the -F/--field option instead, you can see the average >>> weight for the while noploop funciton (as it won't group samples by >> >> %s/funciton/function/ >> >>> weight value and use the default 'comm,dso,sym' sort keys). >>> >>> $ perf report -n -F +weight | grep -e Weight -e noploop >>> # Overhead Samples Weight1 Command Shared Object Symbol >>> 1.23% 7 42.4 perf perf [.] noploop >> >> I think the current +weight shows the sum of weight1 of all samples, >> (global weight). With this patch, it becomes an average (local_weight). >> The definition change may break the existing user script. >> >> Ideally, I think we should keep the meaning of the weight and >> local_weight as is. > > Hmm.. then we may add 'avg_weight' or something. > > But note that there's a subtle difference in the usage. If you use > 'weight' as a sort key (-s weight) it'd keep the existing behavior > that shows the sum (global_weight). It'd show average only if > you use it as an output field (-F weight). >
As my understanding, the -F weight is implicitly replaced by the -F weight1 with this patch. There is no way to get the sum of weight with -F anymore.
I think that's a user visible behavior change. At least, we have to warn the end user with a message, e.g., "weight is not supported with -F anymore. Using weight1 to instead". Only updating the doc may not be enough.
> The issue of the sort key is that it cannot have the total sum > of weights for a function. It'll have separate entries for each > weight for each function like in the above example. >
That seems to be a different issue. If the total sum of weights for a function is required, we should fix the existing "weight".
Thanks, Kan
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