linux-kernel - [RFC PATCH 1/1] libperf: evlist: Fix --cpu argument on hybrid platform

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Message-Id: <20241015145416.583690-2-james.clark@linaro.org>
Date: Tue, 15 Oct 2024 15:54:15 +0100
From: James Clark <james.clark@...aro.org>
To: linux-perf-users@...r.kernel.org,
	acme@...nel.org,
	namhyung@...nel.org,
	irogers@...gle.com
Cc: James Clark <james.clark@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH 1/1] libperf: evlist: Fix --cpu argument on hybrid platform

Since the linked fixes: commit, specifying a CPU on hybrid platforms
results in an error because Perf tries to open an extended type event
on "any" CPU which isn't valid. Extended type events can only be opened
on CPUs that match the type.

Before (working):

  $ perf record --cpu 1 -- true
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 2.385 MB perf.data (7 samples) ]

After (not working):

  $ perf record -C 1 -- true
  WARNING: A requested CPU in '1' is not supported by PMU 'cpu_atom' (CPUs 16-27) for event 'cycles:P'
  Error:
  The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (cpu_atom/cycles:P/).
  /bin/dmesg | grep -i perf may provide additional information.

(Ignore the warning message, that's expected and not particularly
relevant to this issue).

This is because perf_cpu_map__intersect() of the user specified CPU (1)
and one of the PMU's CPUs (16-27) correctly results in an empty (NULL)
CPU map. However for the purposes of opening an event, libperf converts
empty CPU maps into an any CPU (-1) which the kernel rejects.

Fix it by deleting evsels with empty CPU maps in the specific case where
user requested CPU maps are evaluated.

Fixes: 251aa040244a ("perf parse-events: Wildcard most "numeric" events")
Signed-off-by: James Clark <james.clark@...aro.org>
---
 tools/lib/perf/evlist.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
index c6d67fc9e57e..8fae9a157a91 100644
--- a/tools/lib/perf/evlist.c
+++ b/tools/lib/perf/evlist.c
@@ -47,6 +47,13 @@ static void __perf_evlist__propagate_maps(struct perf_evlist *evlist,
 		 */
 		perf_cpu_map__put(evsel->cpus);
 		evsel->cpus = perf_cpu_map__intersect(evlist->user_requested_cpus, evsel->own_cpus);
+
+		/*
+		 * Empty cpu lists would eventually get opened as "any" so remove
+		 * genuinely empty ones before they're opened in the wrong place.
+		 */
+		if (perf_cpu_map__is_empty(evsel->cpus))
+			perf_evlist__remove(evlist, evsel);
 	} else if (!evsel->own_cpus || evlist->has_user_cpus ||
 		(!evsel->requires_cpu && perf_cpu_map__has_any_cpu(evlist->user_requested_cpus))) {
 		/*
@@ -80,11 +87,11 @@ static void __perf_evlist__propagate_maps(struct perf_evlist *evlist,

 static void perf_evlist__propagate_maps(struct perf_evlist *evlist)
 {
-	struct perf_evsel *evsel;
+	struct perf_evsel *evsel, *n;

 	evlist->needs_map_propagation = true;

-	perf_evlist__for_each_evsel(evlist, evsel)
+	list_for_each_entry_safe(evsel, n, &evlist->entries, node)
 		__perf_evlist__propagate_maps(evlist, evsel);
 }

-- 
2.34.1