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

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Date:   Thu, 30 Apr 2020 09:54:18 +0100
From:   John Garry <john.garry@...wei.com>
To:     Jiri Olsa <jolsa@...hat.com>, Jin Yao <yao.jin@...ux.intel.com>
CC:     <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>
Subject: Re: [PATCH] perf parse-events: Use strcmp to compare the PMU name

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

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
>>
> 
> .
>