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    SubjectRe: [PATCH v7 3/3] perf-stat: enable counting events for BPF programs
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    > On Jan 19, 2021, at 8:31 AM, Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
    >
    > Em Tue, Jan 19, 2021 at 11:42:49AM -0300, Arnaldo Carvalho de Melo escreveu:
    >> Em Tue, Jan 19, 2021 at 11:31:44AM -0300, Arnaldo Carvalho de Melo escreveu:
    >>> Em Tue, Jan 19, 2021 at 12:48:19AM +0000, Song Liu escreveu:
    >>>>> On Jan 18, 2021, at 11:38 AM, Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
    >>>> We are looking at two issues:
    >>>> 1. Cannot recursively attach;
    >>>> 2. prog FD 3 doesn't have valid btf.
    >>
    >>>> #1 was caused by the verifier disallowing attaching fentry/fexit program
    >>>> to program with type BPF_PROG_TYPE_TRACING (in bpf_check_attach_target).
    >>>> This constraint was added when we only had fentry/fexit in the TRACING
    >>>> type. We have extended the TRACING type to many other use cases, like
    >>>> "tp_btf/", "fmod_ret" and "iter/". Therefore, it is good time to revisit
    >>>> this constraint. I will work on this.
    >>
    >>>> For #2, we require the target program to have BTF. I guess we won't remove
    >>>> this requirement.
    >>
    >>>> While I work on improving #1, could you please test with some kprobe
    >>>> programs? For example, we can use fileslower.py from bcc.
    >>
    >>> Sure, and please consider improving the error messages to state what you
    >>> described above.
    >>
    >> Terminal 1:
    >>
    >> [root@five perf]# perf trace -e 5sec.c
    >> ^C
    >> [root@five perf]# cat 5sec.c
    >> #include <bpf.h>
    >>
    >> #define NSEC_PER_SEC 1000000000L
    >>
    >> int probe(hrtimer_nanosleep, rqtp)(void *ctx, int err, long long sec)
    >> {
    >> return sec / NSEC_PER_SEC == 5;
    >> }
    >>
    >> license(GPL);
    >> [root@five perf]# perf trace -e 5sec.c/max-stack=16/
    >> 0.000 sleep/3739435 perf_bpf_probe:hrtimer_nanosleep(__probe_ip: -1743337312, rqtp: 5000000000)
    >> hrtimer_nanosleep ([kernel.kallsyms])
    >> common_nsleep ([kernel.kallsyms])
    >> __x64_sys_clock_nanosleep ([kernel.kallsyms])
    >> do_syscall_64 ([kernel.kallsyms])
    >> entry_SYSCALL_64_after_hwframe ([kernel.kallsyms])
    >> __clock_nanosleep_2 (/usr/lib64/libc-2.32.so)
    >>
    >>
    >> Terminal 2:
    >>
    >> [root@five ~]# perf stat -e cycles -b 180 -I 1000
    >> libbpf: elf: skipping unrecognized data section(9) .eh_frame
    >> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
    >> perf: util/bpf_counter.c:227: bpf_program_profiler__read: Assertion `skel != NULL' failed.
    >> Aborted (core dumped)
    >
    > Out to lunch, will continue later, but this may help you figure this out
    > till then :)
    >
    > Starting program: /root/bin/perf stat -e cycles -b 244 -I 1000
    > [Thread debugging using libthread_db enabled]
    > Using host libthread_db library "/lib64/libthread_db.so.1".
    >
    > Breakpoint 1, bpf_program_profiler_load_one (evsel=0xce02c0, prog_id=244) at util/bpf_counter.c:96
    > 96 {
    > (gdb) n
    > 104 prog_fd = bpf_prog_get_fd_by_id(prog_id);
    > (gdb)
    > 105 if (prog_fd < 0) {
    > (gdb)
    > 109 counter = bpf_counter_alloc();
    > (gdb)
    > 110 if (!counter) {
    > (gdb) n
    > 115 skel = bpf_prog_profiler_bpf__open();
    > (gdb) p counter
    > $9 = (struct bpf_counter *) 0xce09e0
    > (gdb) p *counter
    > $10 = {skel = 0x0, list = {next = 0xce09e8, prev = 0xce09e8}}
    > (gdb) p *counter
    > $11 = {skel = 0x0, list = {next = 0xce09e8, prev = 0xce09e8}}
    > (gdb) n
    > libbpf: elf: skipping unrecognized data section(9) .eh_frame
    > libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
    > 116 if (!skel) {
    > (gdb)
    > 121 skel->rodata->num_cpu = evsel__nr_cpus(evsel);
    > (gdb)
    > 123 bpf_map__resize(skel->maps.events, evsel__nr_cpus(evsel));
    > (gdb)
    > 124 bpf_map__resize(skel->maps.fentry_readings, 1);
    > (gdb)
    > 125 bpf_map__resize(skel->maps.accum_readings, 1);
    > (gdb)
    > 127 prog_name = bpf_target_prog_name(prog_fd);
    > (gdb)
    > 128 if (!prog_name) {
    > (gdb)
    > 133 bpf_object__for_each_program(prog, skel->obj) {
    > (gdb)
    > 134 err = bpf_program__set_attach_target(prog, prog_fd, prog_name);
    > (gdb)
    > 135 if (err) {
    > (gdb)
    > 133 bpf_object__for_each_program(prog, skel->obj) {
    > (gdb) p evsel
    > $12 = (struct evsel *) 0xce02c0
    > (gdb) p evsel->name
    > $13 = 0xce04e0 "cycles"
    > (gdb) n
    > 134 err = bpf_program__set_attach_target(prog, prog_fd, prog_name);
    > (gdb)
    > 135 if (err) {
    > (gdb)
    > 133 bpf_object__for_each_program(prog, skel->obj) {
    > (gdb)
    > 141 set_max_rlimit();
    > (gdb)
    > 142 err = bpf_prog_profiler_bpf__load(skel);
    > (gdb)
    > 143 if (err) {
    > (gdb)
    > 148 assert(skel != NULL);
    > (gdb)
    > 149 counter->skel = skel;
    > (gdb)
    > 150 list_add(&counter->list, &evsel->bpf_counter_list);
    > (gdb) c
    > Continuing.
    >
    > Breakpoint 4, bpf_program_profiler__install_pe (evsel=0xce02c0, cpu=0, fd=3) at util/bpf_counter.c:247
    > 247 {
    > (gdb) n
    > 252 list_for_each_entry(counter, &evsel->bpf_counter_list, list) {
    > (gdb)
    > 253 skel = counter->skel;
    > (gdb) watch counter->skel
    > Hardware watchpoint 6: counter->skel
    > (gdb) p counter->skel
    > $14 = (void *) 0xce0a00
    > (gdb) n
    > 254 assert(skel != NULL);
    > (gdb) p skel
    > $15 = (struct bpf_prog_profiler_bpf *) 0xce0a00
    > (gdb) c
    > Continuing.
    >
    > Hardware watchpoint 6: counter->skel
    >
    > Old value = (void *) 0xce0a00
    > New value = (void *) 0x0
    > 0x00000000005cf45e in bpf_program_profiler__install_pe (evsel=0xce02c0, cpu=0, fd=3) at util/bpf_counter.c:252
    > 252 list_for_each_entry(counter, &evsel->bpf_counter_list, list) {

    So it was the list operation that set counter->skel to NULL? I am really confused...

    Song

    > (gdb) info b
    > Num Type Disp Enb Address What
    > 1 breakpoint keep y 0x00000000005ceb44 in bpf_program_profiler_load_one at util/bpf_counter.c:96
    > breakpoint already hit 1 time
    > 2 breakpoint keep y 0x00000000005cef2e in bpf_program_profiler__enable at util/bpf_counter.c:192
    > 3 breakpoint keep y 0x00000000005cf00a in bpf_program_profiler__read at util/bpf_counter.c:208
    > 4 breakpoint keep y 0x00000000005cf3ba in bpf_program_profiler__install_pe at util/bpf_counter.c:247
    > breakpoint already hit 1 time
    > 5 breakpoint keep y 0x00000000005ce8d4 in bpf_program_profiler__destroy at util/bpf_counter.c:47
    > 6 hw watchpoint keep y counter->skel
    > breakpoint already hit 1 time
    > (gdb) p evsel
    > $16 = (struct evsel *) 0xce02c0
    > (gdb) bt
    > #0 0x00000000005cf45e in bpf_program_profiler__install_pe (evsel=0xce02c0, cpu=0, fd=3) at util/bpf_counter.c:252
    > #1 0x00000000005cf4f3 in bpf_counter__install_pe (evsel=0xce02c0, cpu=0, fd=3) at util/bpf_counter.c:276
    > #2 0x00000000004f3ef1 in evsel__open_cpu (evsel=0xce02c0, cpus=0xce0500, threads=0xce75c0, start_cpu=0, end_cpu=1) at util/evsel.c:1792
    > #3 0x00000000004f4aa7 in evsel__open_per_cpu (evsel=0xce02c0, cpus=0xce0500, cpu=0) at util/evsel.c:1996
    > #4 0x000000000057f6f2 in create_perf_stat_counter (evsel=0xce02c0, config=0xa97860 <stat_config>, target=0xa97660 <target>, cpu=0) at util/stat.c:568
    > #5 0x0000000000435d96 in __run_perf_stat (argc=0, argv=0x7fffffffdb60, run_idx=0) at builtin-stat.c:790
    > #6 0x00000000004367e3 in run_perf_stat (argc=0, argv=0x7fffffffdb60, run_idx=0) at builtin-stat.c:1001
    > #7 0x0000000000439e35 in cmd_stat (argc=0, argv=0x7fffffffdb60) at builtin-stat.c:2415
    > #8 0x00000000004cf058 in run_builtin (p=0xaabe00 <commands+288>, argc=7, argv=0x7fffffffdb60) at perf.c:312
    > #9 0x00000000004cf2c5 in handle_internal_command (argc=7, argv=0x7fffffffdb60) at perf.c:364
    > #10 0x00000000004cf40c in run_argv (argcp=0x7fffffffd9ac, argv=0x7fffffffd9a0) at perf.c:408
    > #11 0x00000000004cf7d8 in main (argc=7, argv=0x7fffffffdb60) at perf.c:538
    > (gdb) n
    > 261 return 0;
    >

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