> On Mar 2, 2020, at 5:36 AM, Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote: > > Hi Song, > > Thanks for this work! Some remarks (mostly nitpicks) inline. > > 2020-02-28 15:40 UTC-0800 ~ Song Liu <songliubraving@xxxxxx> >> With fentry/fexit programs, it is possible to profile BPF program with >> hardware counters. Introduce bpftool "prog profile", which measures key >> metrics of a BPF program. >> >> bpftool prog profile command creates per-cpu perf events. Then it attaches >> fentry/fexit programs to the target BPF program. The fentry program saves >> perf event value to a map. The fexit program reads the perf event again, >> and calculates the difference, which is the instructions/cycles used by >> the target program. >> >> Example input and output: >> >> ./bpftool prog profile 3 id 337 cycles instructions llc_misses >> >> 4228 run_cnt >> 3403698 cycles (84.08%) >> 3525294 instructions # 1.04 insn per cycle (84.05%) >> 13 llc_misses # 3.69 LLC misses per million isns (83.50%) >> >> This command measures cycles and instructions for BPF program with id >> 337 for 3 seconds. The program has triggered 4228 times. The rest of the >> output is similar to perf-stat. In this example, the counters were only >> counting ~84% of the time because of time multiplexing of perf counters. >> >> Note that, this approach measures cycles and instructions in very small >> increments. So the fentry/fexit programs introduce noticeable errors to >> the measurement results. >> >> The fentry/fexit programs are generated with BPF skeletons. Therefore, we >> build bpftool twice. The first time _bpftool is built without skeletons. >> Then, _bpftool is used to generate the skeletons. The second time, bpftool >> is built with skeletons. >> >> Signed-off-by: Song Liu <songliubraving@xxxxxx> >> --- Thanks Yonghong and Quentin! I will fix these and send v3. Song
