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Date:   Tue, 29 Dec 2020 19:11:12 +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 10:48 AM, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> 
> Em Tue, Dec 29, 2020 at 06:42:18PM +0000, Song Liu escreveu:
>> 
>> 
>>> On Dec 29, 2020, at 7:15 AM, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
>>> 
>>> Em Mon, Dec 28, 2020 at 11:43:25PM +0000, Song Liu escreveu:
>>>> 
>>>> 
>>>>> On Dec 28, 2020, at 12:11 PM, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
>>>>> 
>>>>> Em Mon, Dec 28, 2020 at 09:40:53AM -0800, Song Liu escreveu:
>>>>>> Introduce perf-stat -b option, which counts events for BPF programs, like:
>>>>>> 
>>>>>> [root@...alhost ~]# ~/perf stat -e ref-cycles,cycles -b 254 -I 1000
>>>>>>   1.487903822            115,200      ref-cycles
>>>>>>   1.487903822             86,012      cycles
>>>>>>   2.489147029             80,560      ref-cycles
>>>>>>   2.489147029             73,784      cycles
>>>>>>   3.490341825             60,720      ref-cycles
>>>>>>   3.490341825             37,797      cycles
>>>>>>   4.491540887             37,120      ref-cycles
>>>>>>   4.491540887             31,963      cycles
>>>>>> 
>>>>>> The example above counts cycles and ref-cycles of BPF program of id 254.
>>>>>> This is similar to bpftool-prog-profile command, but more flexible.
>>>>>> 
>>>>>> perf-stat -b creates per-cpu perf_event and loads fentry/fexit BPF
>>>>>> programs (monitor-progs) to the target BPF program (target-prog). The
>>>>>> monitor-progs read perf_event before and after the target-prog, and
>>>>>> aggregate the difference in a BPF map. Then the user space reads data
>>>>>> from these maps.
>>>>>> 
>>>>>> A new struct bpf_counter is introduced to provide common interface that
>>>>>> uses BPF programs/maps to count perf events.
>>>>> 
>>>>> Segfaulting here:
>>>>> 
>>>>> [root@...e ~]# bpftool prog  | grep tracepoint
>>>>> 110: tracepoint  name syscall_unaugme  tag 57cd311f2e27366b  gpl
>>>>> 111: tracepoint  name sys_enter_conne  tag 3555418ac9476139  gpl
>>>>> 112: tracepoint  name sys_enter_sendt  tag bc7fcadbaf7b8145  gpl
>>>>> 113: tracepoint  name sys_enter_open  tag 0e59c3ac2bea5280  gpl
>>>>> 114: tracepoint  name sys_enter_opena  tag 0baf443610f59837  gpl
>>>>> 115: tracepoint  name sys_enter_renam  tag 24664e4aca62d7fa  gpl
>>>>> 116: tracepoint  name sys_enter_renam  tag 20093e51a8634ebb  gpl
>>>>> 117: tracepoint  name sys_enter  tag 0bc3fc9d11754ba1  gpl
>>>>> 118: tracepoint  name sys_exit  tag 29c7ae234d79bd5c  gpl
>>>>> [root@...e ~]#
>>>>> [root@...e ~]# gdb perf
>>>>> GNU gdb (GDB) Fedora 10.1-2.fc33
>>>>> Reading symbols from perf...
>>>>> (gdb) run stat -e instructions,cycles -b 113 -I 1000
>>>>> Starting program: /root/bin/perf stat -e instructions,cycles -b 113 -I 1000
>>>>> [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
>>>>> 
>>>>> Program received signal SIGSEGV, Segmentation fault.
>>>>> 0x000000000058d55b in bpf_program_profiler__read (evsel=0xc612c0) at util/bpf_counter.c:217
>>>>> 217			reading_map_fd = bpf_map__fd(skel->maps.accum_readings);
>>>>> (gdb) bt
>>>>> #0  0x000000000058d55b in bpf_program_profiler__read (evsel=0xc612c0) at util/bpf_counter.c:217
>>>>> #1  0x0000000000000000 in ?? ()
>>>>> (gdb)
>>>>> 
>>>>> [acme@...e perf]$ clang -v |& head -2
>>>>> clang version 11.0.0 (Fedora 11.0.0-2.fc33)
>>>>> Target: x86_64-unknown-linux-gnu
>>>>> [acme@...e perf]$
>>>>> 
>>>>> Do you need any extra info?
>>>> 
>>>> Hmm... I am not able to reproduce this. I am trying to setup an environment similar
>>>> to fc33 (clang 11, etc.). Does this segfault every time, and on all programs? 
>>> 
>>> I'll try it with a BPF proggie attached to a kprobes, but here is
>>> something else I noticed:
>>> 
>>> [root@...e perf]# export PYTHONPATH=/tmp/build/perf/python
>>> [root@...e perf]# tools/perf/python/twatch.py
>>> Traceback (most recent call last):
>>> File "/home/acme/git/perf/tools/perf/python/twatch.py", line 9, in <module>
>>>   import perf
>>> ImportError: /tmp/build/perf/python/perf.cpython-39-x86_64-linux-gnu.so: undefined symbol: bpf_counter__destroy
>>> [root@...e perf]# perf test python
>>> 19: 'import perf' in python                                         : FAILED!
>>> [root@...e perf]# perf test -v python
>>> 19: 'import perf' in python                                         :
>>> --- start ---
>>> test child forked, pid 3198864
>>> python usage test: "echo "import sys ; sys.path.append('/tmp/build/perf/python'); import perf" | '/usr/bin/python3' "
>>> Traceback (most recent call last):
>>> File "<stdin>", line 1, in <module>
>>> ImportError: /tmp/build/perf/python/perf.cpython-39-x86_64-linux-gnu.so: undefined symbol: bpf_counter__destroy
>>> test child finished with -1
>>> ---- end ----
>>> 'import perf' in python: FAILED!
>>> [root@...e perf]#
>>> 
>>> This should be trivial, I hope, just add the new object file to
>>> tools/perf/util/python-ext-sources, then do a 'perf test python', if it
>>> fails, use 'perf test -v python' to see what is preventing the python
>>> binding from loading.
>> 
>> I fixed the undefined bpf_counter__destroy. But this one looks trickier:
>> 
>> 19: 'import perf' in python                                         :
>> --- start ---
>> test child forked, pid 2714986
>> python usage test: "echo "import sys ; sys.path.append('python'); import perf" | '/bin/python2' "
>> Traceback (most recent call last):
>>  File "<stdin>", line 1, in <module>
>> ImportError: XXXXX /tools/perf/python/perf.so: undefined symbol: bpf_map_update_elem
>> 
>> Given I already have:
> 
> 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. 

I don't have good ideas with 3 and 4... Shall I send current code as v7?

Thanks,
Song

> 
> - Arnaldo
> 
>> diff --git i/tools/perf/util/python-ext-sources w/tools/perf/util/python-ext-sources
>> index a9d9c142eb7c3..2cac55273eca2 100644
>> --- i/tools/perf/util/python-ext-sources
>> +++ w/tools/perf/util/python-ext-sources
>> @@ -35,3 +35,6 @@ util/symbol_fprintf.c
>> util/units.c
>> util/affinity.c
>> util/rwsem.c
>> +util/bpf_counter.c
>> +../lib/bpf/bpf.c
>> +../lib/bpf/libbpf.c
>> 
>> 
>> How should I fix this? 
>> 
>> Thanks,
>> Song
>> 
>> PS: I still cannot reproduce that segfault...
>> 
>>> 
>> 
> 
> -- 
> 
> - Arnaldo

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