Re: [PATCH V5 2/8] perf/x86: Add PERF_X86_EVENT_NEEDS_BRANCH_STACK flag

["Liang, Kan" <kan.liang@linux.intel.com>]

On 2023-11-09 11:45 a.m., Arnaldo Carvalho de Melo wrote:
> Em Thu, Nov 09, 2023 at 11:14:31AM -0500, Liang, Kan escreveu:
>>
>>
>> On 2023-11-08 4:31 p.m., Arnaldo Carvalho de Melo wrote:
>>> Em Tue, Nov 07, 2023 at 12:11:50PM -0300, Arnaldo Carvalho de Melo escreveu:
>>>> Em Mon, Nov 06, 2023 at 04:19:13PM -0500, Liang, Kan escreveu:
>>>>> On 2023-11-06 4:12 p.m., Arnaldo Carvalho de Melo wrote:
>>>>>> Em Wed, Oct 25, 2023 at 01:16:20PM -0700, kan.liang@linux.intel.com escreveu:
>>>>> Ian has already reviewed the tool parts.
>>>
>>>>> But I still owe a test case for the feature. I will post a patch later.
>>>>> https://lore.kernel.org/lkml/acbb895a-475e-4679-98fc-6b90c05a00af@linux.intel.com/
>>>
>>>> I saw Ian's suggestion, and agree with it, we need to pair new features
>>>> with regression tests in 'perf test', thanks for working on it!
>>>
>>> Kan,
>>>
>>> 	I still have to bisect, but can you check if this works for you?
>>
>> The branch counters feature requires all the events to belong to a
>> group. There is no problem for the normal perf usage which usually
>> initializes an evlist even for a single evsel.
>> But perf test is special, which may not initialize an evlist. The Sample
>> parsing test case is one of the examples. It crashes with the
>> !evsel->evlist.
>>
>> The below change should fix it. I will post a complete patch shortly.
> 
> Thanks for the quick response, if all that is needed are the checks
> below, I'll fold it into your original patch:
> 
> 2ae01908298426e4 perf tools: Add branch counter knob
> 
> So that we don't regress, ok?

Sure.

I also post the patch to
https://lore.kernel.org/lkml/20231109164007.2037721-1-kan.liang@linux.intel.com/
Either folding it or using the new patch is fine for me.

BTW: the new perf test case for the feature is posted here.
I think Ian is reviewing it.
https://lore.kernel.org/lkml/20231107184020.1497571-1-kan.liang@linux.intel.com/

Thanks,
Kan
> 
> I'll add a note and the Link tag points to this discussion in case
> people want to do historical digs in the future :-)
> 
> - Arnaldo
>  
>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>> index 58a9b8c82790..7a6a2d1f96db 100644
>> --- a/tools/perf/util/evsel.c
>> +++ b/tools/perf/util/evsel.c
>> @@ -2355,6 +2355,10 @@ static inline bool
>> evsel__has_branch_counters(const struct evsel *evsel)
>>  {
>>         struct evsel *cur, *leader = evsel__leader(evsel);
>>
>> +       /* The branch counters feature only supports group */
>> +       if (!leader || !evsel->evlist)
>> +               return false;
>> +
>>         evlist__for_each_entry(evsel->evlist, cur) {
>>                 if ((leader == evsel__leader(cur)) &&
>>                     (cur->core.attr.branch_sample_type &
>> PERF_SAMPLE_BRANCH_COUNTERS))
>>
>> Thanks,
>> Kan
>>
>>>
>>>
>>> (gdb) run test -F -v 27
>>> Starting program: /root/bin/perf test -F -v 27
>>>
>>>  27: Sample parsing                                                  :
>>> --- start ---
>>>
>>> Program received signal SIGSEGV, Segmentation fault.
>>> 0x00000000004e4aa6 in evsel.parse_sample ()
>>> Missing separate debuginfos, use: dnf debuginfo-install bzip2-libs-1.0.8-13.fc38.x86_64 cyrus-sasl-lib-2.1.28-9.fc38.x86_64 elfutils-debuginfod-client-0.189-3.fc38.x86_64 elfutils-libelf-0.189-3.fc38.x86_64 elfutils-libs-0.189-3.fc38.x86_64 glib2-2.76.5-2.fc38.x86_64 glibc-2.37-13.fc38.x86_64 keyutils-libs-1.6.1-6.fc38.x86_64 krb5-libs-1.21-3.fc38.x86_64 libbabeltrace-1.5.11-2.fc38.x86_64 libbrotli-1.0.9-11.fc38.x86_64 libcap-2.48-6.fc38.x86_64 libcom_err-1.46.5-4.fc38.x86_64 libcurl-8.0.1-5.fc38.x86_64 libevent-2.1.12-8.fc38.x86_64 libgcc-13.2.1-4.fc38.x86_64 libidn2-2.3.4-2.fc38.x86_64 libnghttp2-1.52.0-2.fc38.x86_64 libpfm-4.11.0-11.fc38.x86_64 libpsl-0.21.2-2.fc38.x86_64 libselinux-3.5-1.fc38.x86_64 libssh-0.10.5-1.fc38.x86_64 libstdc++-13.2.1-4.fc38.x86_64 libtraceevent-1.7.2-1.fc38.x86_64 libunistring1.0-1.0-1.fc38.x86_64 libunwind-1.6.2-7.fc38.x86_64 libuuid-2.38.1-4.fc38.x86_64 libxcrypt-4.4.36-1.fc38.x86_64 libzstd-1.5.5-1.fc38.x86_64 opencsd-1.3.3-1.fc38.x86_64 openldap-2.6.6-1.fc38.x86_64 openssl-libs-3.0.9-2.fc38.x86_64 perl-libs-5.36.1-497.fc38.x86_64 popt-1.19-2.fc38.x86_64 python3-libs-3.11.6-1.fc38.x86_64 slang-2.3.3-3.fc38.x86_64 zlib-1.2.13-3.fc38.x86_64
>>> (gdb) bt
>>> #0  0x00000000004e4aa6 in evsel.parse_sample ()
>>> #1  0x00000000004b28dc in do_test ()
>>> #2  0x00000000004b2acd in test.sample_parsing ()
>>> #3  0x0000000000495348 in test_and_print.isra ()
>>> #4  0x0000000000495f5d in cmd_test ()
>>> #5  0x00000000004c2a29 in run_builtin ()
>>> #6  0x000000000041053f in main ()
>>> (gdb)
>>>
>