Re: [PATCH v3 4/7] perf arm-spe: Use metadata to decide the data source feature

[James Clark]

On 03/10/2024 7:53 pm, Leo Yan wrote:
> Use the info in the metadata to decide if the data source feature is
> supported. The CPU MIDR must be in the CPU list for the common data
> source encoding.
>
> For the metadata version 1, it doesn't include info for MIDR. In this
> case, due to absent info for making decision, print out warning to
> remind users to upgrade tool and returns false.
>
> Signed-off-by: Leo Yan <leo.yan@xxxxxxx>
> ---
>   tools/perf/util/arm-spe.c | 67 +++++++++++++++++++++++++++++++++++++--
>   1 file changed, 64 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
> index 587943b6bdb8..9221b2f66bbe 100644
> --- a/tools/perf/util/arm-spe.c
> +++ b/tools/perf/util/arm-spe.c
> @@ -278,6 +278,20 @@ static int arm_spe_set_tid(struct arm_spe_queue *speq, pid_t tid)
>   	return 0;
>   }
>   
> +static u64 *arm_spe__get_metadata_by_cpu(struct arm_spe *spe, u64 cpu)
> +{
> +	u64 i;
> +
> +	if (!spe->metadata)
> +		return NULL;
> +
> +	for (i = 0; i < spe->metadata_nr_cpu; i++)
> +		if (spe->metadata[i][ARM_SPE_CPU] == cpu)
> +			return spe->metadata[i];
> +
> +	return NULL;
> +}
> +
>   static struct simd_flags arm_spe__synth_simd_flags(const struct arm_spe_record *record)
>   {
>   	struct simd_flags simd_flags = {};
> @@ -520,10 +534,57 @@ static void arm_spe__synth_memory_level(const struct arm_spe_record *record,
>   		data_src->mem_lvl |= PERF_MEM_LVL_REM_CCE1;
>   }
>   
> -static u64 arm_spe__synth_data_source(const struct arm_spe_record *record, u64 midr)
> +static bool arm_spe__is_common_ds_encoding(struct arm_spe_queue *speq)
> +{
> +	struct arm_spe *spe = speq->spe;
> +	bool is_in_cpu_list;
> +	u64 *metadata = NULL;
> +	u64 midr = 0;
> +
> +	/*
> +	 * Metadata version 1 doesn't contain any info for MIDR.
> +	 * Simply return false in this case.
> +	 */
> +	if (spe->metadata_ver == 1) {
> +		pr_warning_once("The data file contains metadata version 1, "
> +				"which is absent the info for data source. "
> +				"Please upgrade the tool to record data.\n");
> +		return false;
> +	}
> +
> +	/* CPU ID is -1 for per-thread mode */
> +	if (speq->cpu < 0) {
> +		/*
> +		 * On the heterogeneous system, due to CPU ID is -1,
> +		 * cannot confirm the data source packet is supported.
> +		 */
> +		if (!spe->is_homogeneous)
> +			return false;

Technically you could look at timestamps and context switches to find 
the CPU for non-homogeneous per-thread mode. But it's such an edge case 
I'm not sure it's even worth leaving a TODO for.