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Sender: Namhyung Kim <namhyung@gmail.com>
From:   Namhyung Kim <namhyung@kernel.org>
To:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@redhat.com>
Cc:     Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Ian Rogers <irogers@google.com>,
        Stephane Eranian <eranian@google.com>
Subject: [PATCH v2] perf evsel: Fix missing exclude_{host,guest} setting
Date:   Mon, 25 Oct 2021 21:33:51 -0700
Message-Id: <20211026043351.56662-1-namhyung@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The current logic for the perf missing feature has a bug that it can
wrongly clear some modifiers like G or H.  Actually some PMUs don't
support any filtering or exclusion while others do.  But we check it
as a global feature.

For example, the cycles event can have 'G' modifier to enable it only
in the guest mode on x86.  When you don't run any VMs it'll return 0.

  # perf stat -a -e cycles:G sleep 1

    Performance counter stats for 'system wide':

                    0      cycles:G

          1.000721670 seconds time elapsed

But when it's used with other pmu events that don't support G modifier,
it'll be reset and return non-zero values.

  # perf stat -a -e cycles:G,msr/tsc/ sleep 1

    Performance counter stats for 'system wide':

          538,029,960      cycles:G
       16,924,010,738      msr/tsc/

          1.001815327 seconds time elapsed

This is because of the missing feature detection logic being global.
Add a hashmap to set pmu-specific exclude_host/guest features.

Reported-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
v2 changes)
 * change to enum perf_missing_pmu_features
 * pass NULL to hashmap__find() to skip checking
 * add a blank line after declaration

 tools/perf/util/evsel.c | 47 +++++++++++++++++++++++++++++++++++------
 tools/perf/util/evsel.h |  7 ++++++
 2 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index dbfeceb2546c..f33801b4615d 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1434,6 +1434,10 @@ void evsel__delete(struct evsel *evsel)
 {
 	evsel__exit(evsel);
 	free(evsel);
+
+	/* just free it for the first evsel */
+	hashmap__free(perf_missing_features.pmu);
+	perf_missing_features.pmu = NULL;
 }
 
 void evsel__compute_deltas(struct evsel *evsel, int cpu, int thread,
@@ -1791,6 +1795,23 @@ static int __evsel__prepare_open(struct evsel *evsel, struct perf_cpu_map *cpus,
 	return 0;
 }
 
+#define PMU_HASH_BITS  4
+
+static size_t pmu_hash(const void *key, void *ctx __maybe_unused)
+{
+	const struct evsel *evsel = key;
+
+	return hash_bits(evsel->core.attr.type, PMU_HASH_BITS);
+}
+
+static bool pmu_equal(const void *key1, const void *key2, void *ctx __maybe_unused)
+{
+	const struct evsel *a = key1;
+	const struct evsel *b = key2;
+
+	return a->core.attr.type == b->core.attr.type;
+}
+
 static void evsel__disable_missing_features(struct evsel *evsel)
 {
 	if (perf_missing_features.weight_struct) {
@@ -1807,8 +1828,13 @@ static void evsel__disable_missing_features(struct evsel *evsel)
 		evsel->open_flags &= ~(unsigned long)PERF_FLAG_FD_CLOEXEC;
 	if (perf_missing_features.mmap2)
 		evsel->core.attr.mmap2 = 0;
-	if (perf_missing_features.exclude_guest)
-		evsel->core.attr.exclude_guest = evsel->core.attr.exclude_host = 0;
+	if (perf_missing_features.exclude_guest) {
+		/* we only have EXCLUDE_GUEST bit, let's skip checking  */
+		if (hashmap__find(perf_missing_features.pmu, evsel, NULL)) {
+			evsel->core.attr.exclude_guest = 0;
+			evsel->core.attr.exclude_host = 0;
+		}
+	}
 	if (perf_missing_features.lbr_flags)
 		evsel->core.attr.branch_sample_type &= ~(PERF_SAMPLE_BRANCH_NO_FLAGS |
 				     PERF_SAMPLE_BRANCH_NO_CYCLES);
@@ -1840,6 +1866,9 @@ int evsel__prepare_open(struct evsel *evsel, struct perf_cpu_map *cpus,
 
 bool evsel__detect_missing_features(struct evsel *evsel)
 {
+	if (perf_missing_features.pmu == NULL)
+		perf_missing_features.pmu = hashmap__new(pmu_hash, pmu_equal, NULL);
+
 	/*
 	 * Must probe features in the order they were added to the
 	 * perf_event_attr interface.
@@ -1900,10 +1929,16 @@ bool evsel__detect_missing_features(struct evsel *evsel)
 		perf_missing_features.mmap2 = true;
 		pr_debug2_peo("switching off mmap2\n");
 		return true;
-	} else if (!perf_missing_features.exclude_guest &&
-		   (evsel->core.attr.exclude_guest || evsel->core.attr.exclude_host)) {
-		perf_missing_features.exclude_guest = true;
-		pr_debug2_peo("switching off exclude_guest, exclude_host\n");
+	} else if ((evsel->core.attr.exclude_guest || evsel->core.attr.exclude_host) &&
+		   !hashmap__find(perf_missing_features.pmu, evsel, NULL)) {
+		uintptr_t pmu_features = PERF_MISSING_PMU_EXCLUDE_GUEST;
+
+		hashmap__add(perf_missing_features.pmu, evsel, (void *)pmu_features);
+
+		if (!perf_missing_features.exclude_guest) {
+			perf_missing_features.exclude_guest = true;
+			pr_debug2_peo("switching off exclude_guest, exclude_host\n");
+		}
 		return true;
 	} else if (!perf_missing_features.sample_id_all) {
 		perf_missing_features.sample_id_all = true;
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 1f7edfa8568a..11b5ece19f0e 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -172,6 +172,13 @@ struct perf_missing_features {
 	bool data_page_size;
 	bool code_page_size;
 	bool weight_struct;
+
+	/* contains enum perf_missing_pmu_features below */
+	struct hashmap *pmu;
+};
+
+enum perf_missing_pmu_features {
+	PERF_MISSING_PMU_EXCLUDE_GUEST		= 1UL << 0,
 };
 
 extern struct perf_missing_features perf_missing_features;
-- 
2.33.0.1079.g6e70778dc9-goog