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

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Message-ID: <20200430111551.GC1694693@krava>
Date:   Thu, 30 Apr 2020 13:15:51 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     John Garry <john.garry@...wei.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
Subject: Re: [PATCH] perf parse-events: Use strcmp to compare the PMU name

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?

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
> > > 
> > 
> > .
> > 
>