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SubjectRe: [PATCH v6 10/12] perf tools: Improve IBS error handling
From
Stephane,

On 16-Mar-22 5:33 AM, Stephane Eranian wrote:
> On Tue, Mar 15, 2022 at 12:46 AM Ravi Bangoria <ravi.bangoria@amd.com> wrote:
>>
>> Stephane,
>>
>> On 09-Feb-22 2:46 AM, Stephane Eranian wrote:
>>> From: Kim Phillips <kim.phillips@amd.com>
>>>
>>> improve the error message returned on failed perf_event_open() on AMD when
>>> using IBS.
>>>
>>> Output of executing 'perf record -e ibs_op// true' BEFORE this patch:
>>>
>>> The sys_perf_event_open() syscall returned with 22 (Invalid argument)for event (ibs_op//u).
>>> /bin/dmesg | grep -i perf may provide additional information.
>>>
>>> Output after:
>>>
>>> AMD IBS cannot exclude kernel events. Try running at a higher privilege level.
>>>
>>> Output of executing 'sudo perf record -e ibs_op// true' BEFORE this patch:
>>>
>>> Error:
>>> The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (ibs_op//).
>>> /bin/dmesg | grep -i perf may provide additional information.
>>>
>>> Output after:
>>>
>>> Error:
>>> AMD IBS may only be available in system-wide/per-cpu mode. Try using -a, or -C and workload affinity
>>
>> This patch seems to be causing regression to perf python test.
>>
>> Without this patch:
>>
>> $ sudo ./perf test -vvv 19
>> 19: 'import perf' in python :
>> --- start ---
>> test child forked, pid 145391
>> python usage test: "echo "import sys ; sys.path.append('python'); import perf" | '/usr/bin/python2' "
>> test child finished with 0
>> ---- end ----
>> 'import perf' in python: Ok
>>
>> With this patch:
>>
>> $ sudo ./perf test -vvv 19
>> 19: 'import perf' in python :
>> --- start ---
>> test child forked, pid 144415
>> python usage test: "echo "import sys ; sys.path.append('python'); import perf" | '/usr/bin/python2' "
>> Traceback (most recent call last):
>> File "<stdin>", line 1, in <module>
>> ImportError: python/perf.so: undefined symbol: perf_env__cpuid
>> test child finished with -1
>> ---- end ----
>> 'import perf' in python: FAILED!
>>
>
> The fix I sent you is just to prevent a potential SEGFAULT in
> is_amd_ibs(). I bet the test fails some perf_event_open()
> and ends up in strerror function and from there I don't see how the
> patch could impact the test, given you'd segfault
> otherwise.
>
> I tried on my side and with or without this patch this test fails. I
> think this looks like an unrelated issue.

That's strange. IIUC, python/perf.so needs to know about util/evsel.c
which can be done by adding an entry in util/python-ext-sources.

In any case, do we really need this patch now? For both the example given
in description, I see no difference with or without patch:

Without patch:

$ sudo ./perf record -e ibs_op// true
Error:
Invalid event (ibs_op//) in per-thread mode, enable system wide with '-a'.

$ ./perf record -e ibs_op// true
Error:
Invalid event (ibs_op//u) in per-thread mode, enable system wide with '-a'.

Same o/p with the patch as well.

Thanks,
Ravi

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