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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

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) {
(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;