Re: [PATCH v2 1/5] perf arm-spe: Define metadata header version 2

From: Leo Yan
Date: Fri Sep 27 2024 - 04:14:12 EST


On 9/27/24 07:32, Namhyung Kim wrote:

[...]

diff --git a/tools/perf/util/arm-spe.h b/tools/perf/util/arm-spe.h
index 4f4900c18f3e..5416d4e1d15f 100644
--- a/tools/perf/util/arm-spe.h
+++ b/tools/perf/util/arm-spe.h
@@ -12,10 +12,46 @@
enum {
ARM_SPE_PMU_TYPE,
ARM_SPE_PER_CPU_MMAPS,
+ ARM_SPE_AUXTRACE_V1_PRIV_MAX,
+};
+
+#define ARM_SPE_AUXTRACE_V1_PRIV_SIZE \
+ (ARM_SPE_AUXTRACE_V1_PRIV_MAX * sizeof(u64))
+
+enum {
+ /*
+ * The old metadata format (defined above) does not include a
+ * field for version number. Version 1 is reserved and starts
+ * from version 2.
+ */
+ ARM_SPE_HEADER_VERSION,
+ /* Number of sizeof(u64) */
+ ARM_SPE_HEADER_SIZE,
+ /* PMU type shared by CPUs */
+ ARM_SPE_SHARED_PMU_TYPE,
+ /* Number of CPUs */
+ ARM_SPE_CPUS_NUM,
ARM_SPE_AUXTRACE_PRIV_MAX,
};

Why don't you define something like struct arm_spe_header_v2 ?

Here the target is to make metadata to be self-described and can be
easily extended for new version (but I would not expect updating header
will happen frequently).

The fields ARM_SPE_HEADER_VERSION and ARM_SPE_HEADER_SIZE give a
header version and a header size. This allows us to easily extend new
enum items for new header. A benefit is we can use general code for
decoding because we don't need to process structure for a specific
version.

Thanks for review!

Leo