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Subject: Re: [PATCH] perf parse-events: Use strcmp to compare the PMU name
To:     John Garry <john.garry@huawei.com>, Jiri Olsa <jolsa@redhat.com>
Cc:     acme@kernel.org, jolsa@kernel.org, peterz@infradead.org,
        mingo@redhat.com, alexander.shishkin@linux.intel.com,
        Linux-kernel@vger.kernel.org, ak@linux.intel.com,
        kan.liang@intel.com, yao.jin@intel.com,
        "irogers@google.com" <irogers@google.com>
References: <20200430003618.17002-1-yao.jin@linux.intel.com>
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 <20200430111551.GC1694693@krava>
 <0195184b-0b43-f2fd-8d80-3b70d3f5a950@huawei.com>
From:   "Jin, Yao" <yao.jin@linux.intel.com>
Message-ID: <8685d584-1d28-4648-8d85-2ea637f3c695@linux.intel.com>
Date:   Thu, 30 Apr 2020 21:38:34 +0800
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Hi John, Jiri,

On 4/30/2020 7:48 PM, John Garry wrote:
> On 30/04/2020 12:15, Jiri Olsa wrote:
> 
> +
> 
>> On Thu, Apr 30, 2020 at 09:54:18AM +0100, John Garry wrote:
>>> On 30/04/2020 09:45, Jiri Olsa wrote:
>>>> On Thu, Apr 30, 2020 at 08:36:18AM +0800, Jin Yao wrote:
>>>>> A big uncore event group is split into multiple small groups which
>>>>> only include the uncore events from the same PMU. This has been
>>>>> supported in the commit 3cdc5c2cb924a ("perf parse-events: Handle
>>>>> uncore event aliases in small groups properly").
>>>>>
>>>>> If the event's PMU name starts to repeat, it must be a new event.
>>>>> That can be used to distinguish the leader from other members.
>>>>> But now it only compares the pointer of pmu_name
>>>>> (leader->pmu_name == evsel->pmu_name).
>>>>>
>>>>> If we use "perf stat -M LLC_MISSES.PCIE_WRITE -a" on cascadelakex,
>>>>> the event list is:
>>>>>
>>>>> evsel->name                    evsel->pmu_name
>>>>> ---------------------------------------------------------------
>>>>> unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_4 (as leader)
>>>>> unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_2
>>>>> unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_0
>>>>> unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_5
>>>>> unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_3
>>>>> unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_1
>>>>> unc_iio_data_req_of_cpu.mem_write.part1        uncore_iio_4
>>>>> ......
>>>>>
>>>>> For the event "unc_iio_data_req_of_cpu.mem_write.part1" with
>>>>> "uncore_iio_4", it should be the event from PMU "uncore_iio_4".
>>>>> It's not a new leader for this PMU.
>>>>>
>>>>> But if we use "(leader->pmu_name == evsel->pmu_name)", the check
>>>>> would be failed and the event is stored to leaders[] as a new
>>>>> PMU leader.
>>>>>
>>>>> So this patch uses strcmp to compare the PMU name between events.
>>>>>
>>>>> Fixes: 3cdc5c2cb924a ("perf parse-events: Handle uncore event aliases in 
>>>>> small groups properly")
>>>>> Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
>>>>
>>>> looks good, any chance we could have automated test
>>>> for this uncore leader setup logic? like maybe the way
>>>> John did the pmu-events tests? like test will trigger
>>>> only when there's the pmu/events in the system
>>>>
>>>> Acked-by: Jiri Olsa <jolsa@redhat.com>
>>>>
>>>> thanks,
>>>> jirka
>>>
>>> Hi jirka,
>>>
>>> JFYI, this is effectively the same patch as I mentioned to you, which was a
>>> fix for the same WARN:
>>>
>>> https://lore.kernel.org/linux-arm-kernel/1587120084-18990-2-git-send-email-john.garry@huawei.com/ 
>>>
>>>
>>> but I found that it "fixed" d4953f7ef1a2 ("perf parse-events: Fix 3 use
>>> after frees found with clang ASANutil/parse-events.c"), based on bisect
>>> breakage
>>
>> hum right.. sorry I did not recalled that, there's
>> also the warn removal in here, could you guys also
>> plz sync on the fixes clauses?
> 
> I just thought that it fixes d4953f7ef1a2, as I found that the pointer equality 
> fails from that commit. I assume the parse-events code was sound before then (in 
> that regard). That's all I know :)
> 
> Thanks!
> 

For 3cdc5c2cb924a, I just think it should use strcmp for pmu_name comparison 
rather than using pointer. But I'm OK to add d4953f7ef1a2 in fixes clauses. :)

Thanks
Jin Yao

>>
>> thanks,
>> jirka
>>
>>>
>>> cheers
>>>
>>>>
>>>>
>>>>> ---
>>>>>    tools/perf/util/parse-events.c | 5 ++---
>>>>>    1 file changed, 2 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
>>>>> index 10107747b361..786eddb6a097 100644
>>>>> --- a/tools/perf/util/parse-events.c
>>>>> +++ b/tools/perf/util/parse-events.c
>>>>> @@ -1629,12 +1629,11 @@ parse_events__set_leader_for_uncore_aliase(char 
>>>>> *name, struct list_head *list,
>>>>>             * event. That can be used to distinguish the leader from
>>>>>             * other members, even they have the same event name.
>>>>>             */
>>>>> -        if ((leader != evsel) && (leader->pmu_name == evsel->pmu_name)) {
>>>>> +        if ((leader != evsel) &&
>>>>> +            !strcmp(leader->pmu_name, evsel->pmu_name)) {
>>>>>                is_leader = false;
>>>>>                continue;
>>>>>            }
>>>>> -        /* The name is always alias name */
>>>>> -        WARN_ON(strcmp(leader->name, evsel->name));
>>>>>            /* Store the leader event for each PMU */
>>>>>            leaders[nr_pmu++] = (uintptr_t) evsel;
>>>>> -- 
>>>>> 2.17.1
>>>>>
>>>>
>>>> .
>>>>
>>>
>>
>> .
>>
>