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

From: John Garry
Date: Thu Apr 30 2020 - 04:55:04 EST


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


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