Re: [PATCH v7 3/3] perf-stat: enable counting events for BPF programs

[Song Liu]

> On Jan 19, 2021, at 8:31 AM, Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> 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@xxxxxxxxxx> 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;
>