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Message-ID: <20210119163123.GM12699@kernel.org>
Date: Tue, 19 Jan 2021 13:31:23 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Song Liu <songliubraving@...com>
Cc: open list <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Namhyung Kim <namhyung@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Jiri Olsa <jolsa@...hat.com>, Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v7 3/3] perf-stat: enable counting events for BPF programs
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@...nel.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@...e perf]# perf trace -e 5sec.c
> ^C
> [root@...e 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@...e 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@...e ~]# 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;
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