Date:   Tue,  4 Jan 2022 22:13:04 -0800
In-Reply-To: <20220105061351.120843-1-irogers@google.com>
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References: <20220105061351.120843-1-irogers@google.com>
Subject: [PATCH v4 01/48] libperf: Add comments to perf_cpu_map.
From:   Ian Rogers <irogers@google.com>
To:     Andi Kleen <ak@linux.intel.com>, Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        John Garry <john.garry@huawei.com>,
        Kajol Jain <kjain@linux.ibm.com>,
        "Paul A . Clarke" <pc@us.ibm.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Riccardo Mancini <rickyman7@gmail.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        Vineet Singh <vineet.singh@intel.com>,
        James Clark <james.clark@arm.com>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Mike Leach <mike.leach@linaro.org>,
        Leo Yan <leo.yan@linaro.org>, coresight@lists.linaro.org,
        linux-arm-kernel@lists.infradead.org, zhengjun.xing@intel.com
Cc:     eranian@google.com, Ian Rogers <irogers@google.com>
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Precedence: bulk

A particular observed problem is confusing the index with the CPU value,
documentation should hopefully reduce this type of problem.

Reviewed-by: James Clark <james.clark@arm.com>
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/lib/perf/include/internal/cpumap.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/lib/perf/include/internal/cpumap.h b/tools/lib/perf/include/internal/cpumap.h
index 840d4032587b..4054169c12c5 100644
--- a/tools/lib/perf/include/internal/cpumap.h
+++ b/tools/lib/perf/include/internal/cpumap.h
@@ -4,9 +4,18 @@
 
 #include <linux/refcount.h>
 
+/**
+ * A sized, reference counted, sorted array of integers representing CPU
+ * numbers. This is commonly used to capture which CPUs a PMU is associated
+ * with. The indices into the cpumap are frequently used as they avoid having
+ * gaps if CPU numbers were used. For events associated with a pid, rather than
+ * a CPU, a single dummy map with an entry of -1 is used.
+ */
 struct perf_cpu_map {
 	refcount_t	refcnt;
+	/** Length of the map array. */
 	int		nr;
+	/** The CPU values. */
 	int		map[];
 };
 
-- 
2.34.1.448.ga2b2bfdf31-goog