[PATCH v4 0/7] perf: Stream comparison
Sometimes, a small change in a hot function reducing the cycles of this function, but the overall workload doesn't get faster. It is interesting where the cycles are moved to. What it would like is to diff before/after streams. The stream is the branch history which is aggregated by the branch records from perf samples. For example, the callchains aggregated from the branch records. By browsing the hot stream, we can understand the hot code path. By browsing the hot streams, we can understand the hot code path. By comparing the cycles variation of same streams between old perf data and new perf data, we can understand if the cycles are moved to other codes. The before stream is the stream in perf.data.old. The after stream is the stream in perf.data. Diffing before/after streams compares top N hottest streams between two perf data files. If all entries of one stream in perf.data.old are fully matched with all entries of another stream in perf.data, we think two streams are matched, otherwise the streams are not matched. For example, cycles: 1, hits: 26.80% cycles: 1, hits: 27.30% -- -- main div.c:39 main div.c:39 main div.c:44 main div.c:44 The above streams are matched and we can see for the same streams the cycles (1) are equal and the callchain hit percents are slightly changed (26.80% vs. 27.30%). That's expected. Now let's see examples. perf record -b ... Generate perf.data.old with branch data perf record -b ... Generate perf.data with branch data perf diff --stream [ Matched hot streams ] hot chain pair 1: cycles: 1, hits: 27.77% cycles: 1, hits: 9.24% --- -- main div.c:39 main div.c:39 main div.c:44 main div.c:44 hot chain pair 2: cycles: 34, hits: 20.06%cycles: 27, hits: 16.98% --- -- __random_r random_r.c:360 __random_r random_r.c:360 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:380 __random_r random_r.c:380 __random_r random_r.c:357 __random_r random_r.c:357 __random random.c:293 __random random.c:293 __random random.c:293 __random random.c:293 __random random.c:291 __random random.c:291 __random random.c:291 __random random.c:291 __random random.c:291 __random random.c:291 __random random.c:288 __random random.c:288 rand rand.c:27 rand rand.c:27 rand rand.c:26 rand rand.c:26 rand@pltrand@plt rand@pltrand@plt compute_flag div.c:25 compute_flag div.c:25 compute_flag div.c:22 compute_flag div.c:22 main div.c:40 main div.c:40 main div.c:40 main div.c:40 main div.c:39 main div.c:39 hot chain pair 3: cycles: 9, hits: 4.48% cycles: 6, hits: 4.51% --- -- __random_r random_r.c:360 __random_r random_r.c:360 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:380 __random_r random_r.c:380 [ Hot streams in old perf data only ] hot chain 1: cycles: 18, hits: 6.75% -- __random_r random_r.c:360 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:380 __random_r random_r.c:357 __random random.c:293 __random random.c:293 __random random.c:291 __random random.c:291 __random random.c:291 __random random.c:288 rand rand.c:27 rand rand.c:26 rand@plt rand@plt compute_flag div.c:25 compute_flag div.c:22 main div.c:40 hot chain 2: cycles: 29,
[PATCH v4 0/7] perf: Stream comparison
Sometimes, a small change in a hot function reducing the cycles of this function, but the overall workload doesn't get faster. It is interesting where the cycles are moved to. What it would like is to diff before/after streams. The stream is the branch history which is aggregated by the branch records from perf samples. For example, the callchains aggregated from the branch records. By browsing the hot stream, we can understand the hot code path. By browsing the hot streams, we can understand the hot code path. By comparing the cycles variation of same streams between old perf data and new perf data, we can understand if the cycles are moved to other codes. The before stream is the stream in perf.data.old. The after stream is the stream in perf.data. Diffing before/after streams compares top N hottest streams between two perf data files. If all entries of one stream in perf.data.old are fully matched with all entries of another stream in perf.data, we think two streams are matched, otherwise the streams are not matched. For example, cycles: 1, hits: 26.80% cycles: 1, hits: 27.30% -- -- main div.c:39 main div.c:39 main div.c:44 main div.c:44 The above streams are matched and we can see for the same streams the cycles (1) are equal and the callchain hit percents are slightly changed (26.80% vs. 27.30%). That's expected. Now let's see examples. perf record -b ... Generate perf.data.old with branch data perf record -b ... Generate perf.data with branch data perf diff --stream [ Matched hot streams ] hot chain pair 1: cycles: 1, hits: 27.77% cycles: 1, hits: 9.24% --- -- main div.c:39 main div.c:39 main div.c:44 main div.c:44 hot chain pair 2: cycles: 34, hits: 20.06%cycles: 27, hits: 16.98% --- -- __random_r random_r.c:360 __random_r random_r.c:360 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:380 __random_r random_r.c:380 __random_r random_r.c:357 __random_r random_r.c:357 __random random.c:293 __random random.c:293 __random random.c:293 __random random.c:293 __random random.c:291 __random random.c:291 __random random.c:291 __random random.c:291 __random random.c:291 __random random.c:291 __random random.c:288 __random random.c:288 rand rand.c:27 rand rand.c:27 rand rand.c:26 rand rand.c:26 rand@pltrand@plt rand@pltrand@plt compute_flag div.c:25 compute_flag div.c:25 compute_flag div.c:22 compute_flag div.c:22 main div.c:40 main div.c:40 main div.c:40 main div.c:40 main div.c:39 main div.c:39 hot chain pair 3: cycles: 9, hits: 4.48% cycles: 6, hits: 4.51% --- -- __random_r random_r.c:360 __random_r random_r.c:360 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:380 __random_r random_r.c:380 [ Hot streams in old perf data only ] hot chain 1: cycles: 18, hits: 6.75% -- __random_r random_r.c:360 __random_r random_r.c:388 __random_r random_r.c:388 __random_r random_r.c:380 __random_r random_r.c:357 __random random.c:293 __random random.c:293 __random random.c:291 __random random.c:291 __random random.c:291 __random random.c:288 rand rand.c:27 rand rand.c:26 rand@plt rand@plt compute_flag div.c:25 compute_flag div.c:22 main div.c:40 hot chain 2: cycles: 29,
