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Message-ID: <7491af6f-7be8-4a7a-8f48-249d26440bbc@linux.intel.com>
Date: Tue, 16 Jul 2024 08:52:55 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Ian Rogers <irogers@...gle.com>
Cc: kernel test robot <oliver.sang@...el.com>, oe-lkp@...ts.linux.dev,
lkp@...el.com, Linux Memory Management List <linux-mm@...ck.org>,
Namhyung Kim <namhyung@...nel.org>, Weilin Wang <weilin.wang@...el.com>,
Caleb Biggers <caleb.biggers@...el.com>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [linux-next:master] [perf vendor events] e2641db83f:
perf-sanity-tests.perf_all_PMU_test.fail
On 2024-07-15 5:48 p.m., Ian Rogers wrote:
> On Mon, Jul 15, 2024 at 2:41 PM Liang, Kan <kan.liang@...ux.intel.com> wrote:
>>
>>
>>
>> On 2024-07-15 4:11 p.m., Ian Rogers wrote:
>>> On Mon, Jul 15, 2024 at 1:05 PM Liang, Kan <kan.liang@...ux.intel.com> wrote:
>>>>
>>>> Hi Ian,
>>>>
>>>> On 2024-07-10 12:59 a.m., kernel test robot wrote:
>>>>>
>>>>>
>>>>> Hello,
>>>>>
>>>>> kernel test robot noticed "perf-sanity-tests.perf_all_PMU_test.fail" on:
>>>>>
>>>>> commit: e2641db83f18782f57a0e107c50d2d1731960fb8 ("perf vendor events: Add/update skylake events/metrics")
>>>>> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
>>>>>
>>>>> [test failed on linux-next/master 82d01fe6ee52086035b201cfa1410a3b04384257]
>>>>>
>>>>> in testcase: perf-sanity-tests
>>>>> version:
>>>>> with following parameters:
>>>>>
>>>>> perf_compiler: gcc
>>>>>
>>>>>
>>>>>
>>>>> compiler: gcc-13
>>>>> test machine: 16 threads 1 sockets Intel(R) Xeon(R) E-2278G CPU @ 3.40GHz (Coffee Lake) with 32G memory
>>>>>
>>>>> (please refer to attached dmesg/kmsg for entire log/backtrace)
>>>>>
>>>>>
>>>>> we also observed two cases which also failed on parent can pass on this commit.
>>>>> FYI.
>>>>>
>>>>>
>>>>> caccae3ce7b988b6 e2641db83f18782f57a0e107c50
>>>>> ---------------- ---------------------------
>>>>> fail:runs %reproduction fail:runs
>>>>> | | |
>>>>> :6 100% 6:6 perf-sanity-tests.perf_all_PMU_test.fail
>>>>> :6 100% 6:6 perf-sanity-tests.perf_all_metricgroups_test.pass
>>>>> :6 100% 6:6 perf-sanity-tests.perf_all_metrics_test.pass
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>>>>> the same patch/commit), kindly add following tags
>>>>> | Reported-by: kernel test robot <oliver.sang@...el.com>
>>>>> | Closes: https://lore.kernel.org/oe-lkp/202407101021.2c8baddb-oliver.sang@intel.com
>>>>>
>>>>>
>>>>>
>>>>> 2024-07-09 07:09:53 sudo /usr/src/linux-perf-x86_64-rhel-8.3-bpf-e2641db83f18782f57a0e107c50d2d1731960fb8/tools/perf/perf test 105
>>>>> 105: perf all metricgroups test : Ok
>>>>> 2024-07-09 07:10:11 sudo /usr/src/linux-perf-x86_64-rhel-8.3-bpf-e2641db83f18782f57a0e107c50d2d1731960fb8/tools/perf/perf test 106
>>>>> 106: perf all metrics test : Ok
>>>>> 2024-07-09 07:10:23 sudo /usr/src/linux-perf-x86_64-rhel-8.3-bpf-e2641db83f18782f57a0e107c50d2d1731960fb8/tools/perf/perf test 107
>>>>> 107: perf all libpfm4 events test : Ok
>>>>> 2024-07-09 07:10:47 sudo /usr/src/linux-perf-x86_64-rhel-8.3-bpf-e2641db83f18782f57a0e107c50d2d1731960fb8/tools/perf/perf test 108
>>>>> 108: perf all PMU test : FAILED!
>>>>>
>>>>
>>>> The failure is caused by the below change in the e2641db83f18.
>>>>
>>>> + {
>>>> + "BriefDescription": "This 48-bit fixed counter counts the UCLK
>>>> cycles",
>>>> + "Counter": "FIXED",
>>>> + "EventCode": "0xff",
>>>> + "EventName": "UNC_CLOCK.SOCKET",
>>>> + "PerPkg": "1",
>>>> + "PublicDescription": "This 48-bit fixed counter counts the UCLK
>>>> cycles.",
>>>> + "Unit": "cbox_0"
>>>> }
>>>>
>>>> The other cbox events have the unit name "CBOX", while the fixed counter
>>>> has a unit name "cbox_0". So the events_table will maintain separate
>>>> entries for cbox and cbox_0.
>>>>
>>>> The perf_pmus__print_pmu_events() calculate the total number of events,
>>>> allocate an aliases buffer, store all the events into the buffer, sort,
>>>> and print all the aliases one by one.
>>>>
>>>> The problem is that the calculated total number of events doesn't match
>>>> the stored events on the SKL machine.
>>>>
>>>> The perf_pmu__num_events() is used to calculate the number of events. It
>>>> invokes the pmu_events_table__num_events() to go through the entire
>>>> events_table to find all events. Because of the
>>>> pmu_uncore_alias_match(), the suffix of uncore PMU will be ignored. So
>>>> the events for cbox and cbox_0 are all counted.
>>>>
>>>> When storing events into the aliases buffer, the
>>>> perf_pmu__for_each_event() only process the events for cbox.
>>>>
>>>> Since a bigger buffer was allocated, the last entry are all 0.
>>>> When printing all the aliases, null will be outputed.
>>>>
>>>> $ perf list pmu
>>>>
>>>> List of pre-defined events (to be used in -e or -M):
>>>>
>>>> (null) [Kernel PMU event]
>>>> branch-instructions OR cpu/branch-instructions/ [Kernel PMU event]
>>>> branch-misses OR cpu/branch-misses/ [Kernel PMU event]
>>>>
>>>>
>>>> I'm thinking of two ways to address it.
>>>> One is to only print all the stored events. The below patch can fix it.
>>>>
>>>> diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
>>>> index 3fcabfd8fca1..2b2f5117ff84 100644
>>>> --- a/tools/perf/util/pmus.c
>>>> +++ b/tools/perf/util/pmus.c
>>>> @@ -485,6 +485,7 @@ void perf_pmus__print_pmu_events(const struct
>>>> print_callbacks *print_cb, void *p
>>>> perf_pmu__for_each_event(pmu, skip_duplicate_pmus, &state,
>>>> perf_pmus__print_pmu_events__callback);
>>>> }
>>>> + len = state.index;
>>>> qsort(aliases, len, sizeof(struct sevent), cmp_sevent);
>>>> for (int j = 0; j < len; j++) {
>>>> /* Skip duplicates */
>>>>
>>>> The only drawback is that perf list will not show the new cbox_0 event.
>>>> (But the event name still works. Users can still apply perf stat -e
>>>> unc_clock.socket.)
>>>>
>>>> Since the cbox_0 event is only available on old machines (SKL and
>>>> earlier), people should already use the equivalent kernel event. It
>>>> doesn't sounds a big issue for me. I prefer this simple fix.
>>>>
>>>> I think the other way would be to modify the perf_pmu__for_each_event()
>>>> to go through all the possible PMUs.
>>>> It seems complicated and may impact others ARCHs (e.g., S390). I haven't
>>>> tried it yet.
>>>>
>>>> What do you think?
>>>> Do you see any other ways to address the issue?
>>>
>>> Ugh. It seems the sizing and then iterating approach is just prone to
>>> keep breaking. Perhaps we can switch to realloc-ed arrays to avoid the
>>> need for perf_pmu__num_events, which seems to be the source of the
>>> problems.
>>>
>>
>> I think a realloc-ed array should have the same drawback as the first
>> way, but bad performance.
>> Because the pmu_add_cpu_aliases() in the perf_pmu__for_each_event() only
>> add the events from the first matched PMU. If we don't fix it, the
>> UNC_CLOCK.SOCKET of cbox_0 will never be displayed.
>
> Ok, but I don't think we need to optimize `perf list` for speed. Fwiw,
> I think this was the fix for the last bug in this code:
> https://lore.kernel.org/r/20240511003601.2666907-1-irogers@google.com
That seems a different issue.
The root cause of this issue should be that different methods are used
between calculating the total number of events and adding the events.
A realloc-ed array should just hide the problem. There will still be an
issue if anyone use the pair of perf_pmu__num_events() and
pmu_add_cpu_aliases() somewhere else later.
It looks like the difference is introduced from the commit e3edd6cf6399
("perf pmu-events: Reduce processed events by passing PMU").
The pmu_events_table__for_each_event() stops immediately once a pmu is
set. But for uncore, especially this case, the method is wrong and
mismatch what perf does in the perf_pmu__num_events().
The below patch can fix it.
diff --git a/tools/perf/pmu-events/jevents.py
b/tools/perf/pmu-events/jevents.py
index ac9b7ca41856..97a3b018f865 100755
--- a/tools/perf/pmu-events/jevents.py
+++ b/tools/perf/pmu-events/jevents.py
@@ -923,7 +923,7 @@ int pmu_events_table__for_each_event(const struct
pmu_events_table *table,
continue;
ret = pmu_events_table__for_each_event_pmu(table, table_pmu, fn, data);
- if (pmu || ret)
+ if (ret)
return ret;
}
return 0;
The event can be displayed by the perf list pmu with the patch.
$ perf list pmu | grep -A 1 clock.socket
unc_clock.socket
[This 48-bit fixed counter counts the UCLK cycles. Unit:
uncore_cbox_0
& perf test "perf all PMU test"
107: perf all PMU test : Ok
I will send the patch shortly.
Thanks,
Kan
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