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

[John Garry]

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@xxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxx>
>
> 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@xxxxxxxxxx/

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
>
> .