linux-kernel - Re: [PATCH] perf parse-events: Use strcmp to compare the PMU name

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Date:   Thu, 30 Apr 2020 12:48:48 +0100
From:   John Garry <john.garry@...wei.com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     Jin Yao <yao.jin@...ux.intel.com>, <acme@...nel.org>,
        <jolsa@...nel.org>, <peterz@...radead.org>, <mingo@...hat.com>,
        <alexander.shishkin@...ux.intel.com>,
        <Linux-kernel@...r.kernel.org>, <ak@...ux.intel.com>,
        <kan.liang@...el.com>, <yao.jin@...el.com>,
        "irogers@...gle.com" <irogers@...gle.com>
Subject: Re: [PATCH] perf parse-events: Use strcmp to compare the PMU name

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@...ux.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@...hat.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!

> 
> 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
>>>>
>>>
>>> .
>>>
>>
> 
> .
>