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Date:   Tue, 29 Dec 2020 21:40:55 +0000
From:   Song Liu <songliubraving@...com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
CC:     lkml <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "jolsa@...hat.com" <jolsa@...hat.com>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v6 3/4] perf-stat: enable counting events for BPF programs



> On Dec 29, 2020, at 11:32 AM, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> 
> Em Tue, Dec 29, 2020 at 04:23:47PM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Tue, Dec 29, 2020 at 04:18:48PM -0300, Arnaldo Carvalho de Melo escreveu:
>>> Em Tue, Dec 29, 2020 at 07:11:12PM +0000, Song Liu escreveu:
>>>>> On Dec 29, 2020, at 10:48 AM, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
>>>>> I'll check this one to get a patch that at least moves the needle here,
>>>>> i.e. probably we can leave supporting bpf counters in the python binding
>>>>> for a later step.
>> 
>>>> Thanks Arnaldo!
>> 
>>>> Currently, I have:
>>>> 1. Fixed issues highlighted by Namhyung;
>>>> 2. Merged 3/4 and 4/4;
>>>> 3. NOT found segfault;
>>>> 4. NOT fixed python import perf. 
> 
> For 3, now with a kprobe:
> 
> [root@...e ~]# bpftool prog | grep hrtimer -A10
> 99: kprobe  name hrtimer_nanosle  tag 0e77bacaf4555f83  gpl
> 	loaded_at 2020-12-29T16:25:34-0300  uid 0
> 	xlated 80B  jited 49B  memlock 4096B
> 	btf_id 253
> [root@...e ~]# perf stat -I 1000 -b 99
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> Segmentation fault (core dumped)
> [root@...e ~]#
> 
> (gdb) run stat -I 1000 -b 99
> Starting program: /root/bin/perf stat -I 1000 -b 99
> Missing separate debuginfos, use: dnf debuginfo-install glibc-2.32-2.fc33.x86_64
> [Thread debugging using libthread_db enabled]
> Using host libthread_db library "/lib64/libthread_db.so.1".
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> 
> Program received signal SIGSEGV, Segmentation fault.
> 0x000000000056559b in bpf_program_profiler__read (evsel=0xc39770) at util/bpf_counter.c:217
> 217			reading_map_fd = bpf_map__fd(skel->maps.accum_readings);
> Missing separate debuginfos, use: dnf debuginfo-install bzip2-libs-1.0.8-4.fc33.x86_64 cyrus-sasl-lib-2.1.27-6.fc33.x86_64 elfutils-debuginfod-client-0.182-1.fc33.x86_64 elfutils-libelf-0.182-1.fc33.x86_64 elfutils-libs-0.182-1.fc33.x86_64 keyutils-libs-1.6-5.fc33.x86_64 krb5-libs-1.18.2-29.fc33.x86_64 libbabeltrace-1.5.8-3.fc33.x86_64 libbrotli-1.0.9-3.fc33.x86_64 libcap-2.26-8.fc33.x86_64 libcom_err-1.45.6-4.fc33.x86_64 libcurl-7.71.1-8.fc33.x86_64 libgcc-10.2.1-9.fc33.x86_64 libidn2-2.3.0-4.fc33.x86_64 libnghttp2-1.41.0-3.fc33.x86_64 libpsl-0.21.1-2.fc33.x86_64 libselinux-3.1-2.fc33.x86_64 libssh-0.9.5-1.fc33.x86_64 libunistring-0.9.10-9.fc33.x86_64 libunwind-1.4.0-4.fc33.x86_64 libuuid-2.36-3.fc33.x86_64 libxcrypt-4.4.17-1.fc33.x86_64 libzstd-1.4.5-5.fc33.x86_64 numactl-libs-2.0.14-1.fc33.x86_64 openldap-2.4.50-5.fc33.x86_64 openssl-libs-1.1.1i-1.fc33.x86_64 pcre-8.44-2.fc33.x86_64 pcre2-10.36-1.fc33.x86_64 perl-libs-5.32.0-464.fc33.x86_64 popt-1.18-2.fc33.x86_64 python3-libs-3.9.1-1.fc33.x86_64 slang-2.3.2-8.fc33.x86_64 xz-libs-5.2.5-3.fc33.x86_64
> (gdb) bt
> #0  0x000000000056559b in bpf_program_profiler__read (evsel=0xc39770) at util/bpf_counter.c:217
> #1  0x0000000000000000 in ?? ()
> (gdb) p skel->maps.accum_readings
> Cannot access memory at address 0x20
> (gdb) p skel
> $1 = (struct bpf_prog_profiler_bpf *) 0x0
> (gdb) list -10
> 202		int reading_map_fd;
> 203		__u32 key = 0;
> 204		int err, cpu;
> 205
> 206		if (list_empty(&evsel->bpf_counter_list))
> 207			return -EAGAIN;
> 208
> 209		for (cpu = 0; cpu < num_cpu; cpu++) {
> 210			perf_counts(evsel->counts, cpu, 0)->val = 0;
> 211			perf_counts(evsel->counts, cpu, 0)->ena = 0;
> (gdb)
> 212			perf_counts(evsel->counts, cpu, 0)->run = 0;
> 213		}
> 214		list_for_each_entry(counter, &evsel->bpf_counter_list, list) {
> 215			struct bpf_prog_profiler_bpf *skel = counter->skel;
> 216
> 217			reading_map_fd = bpf_map__fd(skel->maps.accum_readings);
> 218
> 219			err = bpf_map_lookup_elem(reading_map_fd, &key, values);
> 220			if (err) {
> 221				fprintf(stderr, "failed to read value\n");
> (gdb) p counter->skel
> $2 = (void *) 0x0
> (gdb) p perf_evsel__name(counter)
> No symbol "perf_evsel__name" in current context.
> (gdb) p evsel__name(counter)
> $3 = 0xc77420 "unknown attr type: 13078424"
> (gdb) p evsel->type
> There is no member named type.
> (gdb) p evsel->core.
> attr         cpus         fd           id           ids          node         nr_members   own_cpus     sample_id    system_wide  threads
> (gdb) p evsel->core.attr.type
> $4 = 1
> (gdb) p evsel->core.attr.config
> $5 = 0
> (gdb) p evsel->evlist
> $6 = (struct evlist *) 0xc3cfd0
> (gdb) p evsel->evlist->core.nr_entries
> $7 = 10
> (gdb)
> 
> 
> 10 entries, the default for 'perf stat'
> 
> 
> With just one event:
> 
> (gdb) run stat -e cycles -I 1000 -b 99
> Starting program: /root/bin/perf stat -e cycles -I 1000 -b 99
> Missing separate debuginfos, use: dnf debuginfo-install glibc-2.32-2.fc33.x86_64
> [Thread debugging using libthread_db enabled]
> Using host libthread_db library "/lib64/libthread_db.so.1".
> libbpf: elf: skipping unrecognized data section(9) .eh_frame
> libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
> 
> Program received signal SIGSEGV, Segmentation fault.
> 0x000000000056559b in bpf_program_profiler__read (evsel=0xc392c0) at util/bpf_counter.c:217
> 217			reading_map_fd = bpf_map__fd(skel->maps.accum_readings);
> Missing separate debuginfos, use: dnf debuginfo-install bzip2-libs-1.0.8-4.fc33.x86_64 cyrus-sasl-lib-2.1.27-6.fc33.x86_64 elfutils-debuginfod-client-0.182-1.fc33.x86_64 elfutils-libelf-0.182-1.fc33.x86_64 elfutils-libs-0.182-1.fc33.x86_64 keyutils-libs-1.6-5.fc33.x86_64 krb5-libs-1.18.2-29.fc33.x86_64 libbabeltrace-1.5.8-3.fc33.x86_64 libbrotli-1.0.9-3.fc33.x86_64 libcap-2.26-8.fc33.x86_64 libcom_err-1.45.6-4.fc33.x86_64 libcurl-7.71.1-8.fc33.x86_64 libgcc-10.2.1-9.fc33.x86_64 libidn2-2.3.0-4.fc33.x86_64 libnghttp2-1.41.0-3.fc33.x86_64 libpsl-0.21.1-2.fc33.x86_64 libselinux-3.1-2.fc33.x86_64 libssh-0.9.5-1.fc33.x86_64 libunistring-0.9.10-9.fc33.x86_64 libunwind-1.4.0-4.fc33.x86_64 libuuid-2.36-3.fc33.x86_64 libxcrypt-4.4.17-1.fc33.x86_64 libzstd-1.4.5-5.fc33.x86_64 numactl-libs-2.0.14-1.fc33.x86_64 openldap-2.4.50-5.fc33.x86_64 openssl-libs-1.1.1i-1.fc33.x86_64 pcre-8.44-2.fc33.x86_64 pcre2-10.36-1.fc33.x86_64 perl-libs-5.32.0-464.fc33.x86_64 popt-1.18-2.fc33.x86_64 python3-libs-3.9.1-1.fc33.x86_64 slang-2.3.2-8.fc33.x86_64 xz-libs-5.2.5-3.fc33.x86_64
> (gdb) bt
> #0  0x000000000056559b in bpf_program_profiler__read (evsel=0xc392c0) at util/bpf_counter.c:217
> #1  0x0000000000000000 in ?? ()
> (gdb) p evsel->name
> $1 = 0xc37960 "cycles"
> (gdb) p evsel->bpf_counter_
> bpf_counter_list  bpf_counter_ops
> (gdb) p evsel->bpf_counter_ops
> $2 = (struct bpf_counter_ops *) 0xa08ec0 <bpf_program_profiler_ops>
> (gdb) p evsel->bpf_counter_
> bpf_counter_list  bpf_counter_ops
> (gdb) p evsel->bpf_counter_list
> $3 = {next = 0xc36e18, prev = 0xc36e18}
> (gdb) p evsel->s
> sample_size        side_band          stats              supported          synth_sample_type
> (gdb) list -5
> 207			return -EAGAIN;
> 208
> 209		for (cpu = 0; cpu < num_cpu; cpu++) {
> 210			perf_counts(evsel->counts, cpu, 0)->val = 0;
> 211			perf_counts(evsel->counts, cpu, 0)->ena = 0;
> 212			perf_counts(evsel->counts, cpu, 0)->run = 0;
> 213		}
> 214		list_for_each_entry(counter, &evsel->bpf_counter_list, list) {
> 215			struct bpf_prog_profiler_bpf *skel = counter->skel;
> 216
> (gdb)
> 217			reading_map_fd = bpf_map__fd(skel->maps.accum_readings);
> 218
> 219			err = bpf_map_lookup_elem(reading_map_fd, &key, values);
> 220			if (err) {
> 221				fprintf(stderr, "failed to read value\n");
> 222				return err;
> 223			}
> 224
> 225			for (cpu = 0; cpu < num_cpu; cpu++) {
> 226				perf_counts(evsel->counts, cpu, 0)->val += values[cpu].counter;
> (gdb) p counter->skel
> $4 = (void *) 0x0
> (gdb)
> 
> skel is NULL?!

So it is skel == NULL. In v7 (coming soon), I fixed some issues in the 
allocate/free of skel, and added some assert(). Let's see how that goes..

Thanks,
Song

> 
> I ran out of time, have to go errands now. will bbl.
> 
> - Arnaldo
> 
>>>> I don't have good ideas with 3 and 4... Shall I send current code as v7?
>> 
>>> For 4, please fold the patch below into the relevant patch, we don't
>>> need bpf_counter.h included in util/evsel.h, you even added a forward
>>> declaration for that 'struct bpf_counter_ops'.
>> 
>>> And in general we should refrain from adding extra includes to header
>>> files, .h-ell is not good.
>>> 
>>> Then we provide a stub for that bpf_counter__destroy() so that
>>> util/evsel.o when linked into the perf python biding find it there,
>>> links ok.
>> 
>> Ok, one more stub is needed, I wasn't building all the time with 
>> 
>>  $ make BUILD_BPF_SKEL=1
>> 
>> Ditch the previous patch please, use the one below instead:
>> 
>> - Arnaldo
>> 
>> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
>> index 40e3946cd7518113..8226b1fefa8cf2a3 100644
>> --- a/tools/perf/util/evsel.h
>> +++ b/tools/perf/util/evsel.h
>> @@ -10,7 +10,6 @@
>> #include <internal/evsel.h>
>> #include <perf/evsel.h>
>> #include "symbol_conf.h"
>> -#include "bpf_counter.h"
>> #include <internal/cpumap.h>
>> 
>> struct bpf_object;
>> diff --git a/tools/perf/util/python.c b/tools/perf/util/python.c
>> index cc5ade85a33fc999..278abecb5bdfc0d2 100644
>> --- a/tools/perf/util/python.c
>> +++ b/tools/perf/util/python.c
>> @@ -79,6 +79,27 @@ int metricgroup__copy_metric_events(struct evlist *evlist, struct cgroup *cgrp,
>> 	return 0;
>> }
>> 
>> +/*
>> + * XXX: All these evsel destructors need some better mechanism, like a linked
>> + * list of destructors registered when the relevant code indeed is used instead
>> + * of having more and more calls in perf_evsel__delete(). -- acme
>> + *
>> + * For now, add some more:
>> + *
>> + * Not to drag the BPF bandwagon...
>> + */
>> +void bpf_counter__destroy(struct evsel *evsel);
>> +int bpf_counter__install_pe(struct evsel *evsel, int cpu, int fd);
>> +
>> +void bpf_counter__destroy(struct evsel *evsel __maybe_unused)
>> +{
>> +}
>> +
>> +int bpf_counter__install_pe(struct evsel *evsel __maybe_unused, int cpu __maybe_unused, int fd __maybe_unused)
>> +{
>> +	return 0;
>> +}
>> +
>> /*
>>  * Support debug printing even though util/debug.c is not linked.  That means
>>  * implementing 'verbose' and 'eprintf'.
> 
> -- 
> 
> - Arnaldo

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