[PATCH v5 11/26] perf arm-spe: Set default synthesized event period to 1

[Tengda Wu <wutengda@huaweicloud.com>]

When using --itrace=M for data type profiling on arm64, the 'Percent'
values in perf annotate output are all zero:

Annotate type: 'struct mmu_gather_batch' in [kernel.kallsyms] (15 samples):
============================================================================
 Percent     offset       size  field
    0.00          0       0x10  struct mmu_gather_batch  {
    0.00          0        0x8      struct mmu_gather_batch*    next;
    0.00        0x8        0x4      unsigned int        nr;
    0.00        0xc        0x4      unsigned int        max;
    0.00       0x10          0      struct encoded_page*[]      encoded_pages;
                                };

However, adding the -n option (show-nr-samples) reveals non-zero sample counts:

Annotate type: 'struct mmu_gather_batch' in [kernel.kallsyms] (15 samples):
============================================================================
 Samples     offset       size  field
      15          0       0x10  struct mmu_gather_batch  {
      13          0        0x8      struct mmu_gather_batch*    next;
       2        0x8        0x4      unsigned int        nr;
       0        0xc        0x4      unsigned int        max;
       0       0x10          0      struct encoded_page*[]      encoded_pages;
                                };

The root cause is that when --itrace is used with non-i/y options
(e.g., --itrace=M), the period remains zero after parsing. During
subsequent propagation, the final percentage calculation results
in zero:

   arm_spe_prep_sample()
      sample->period = spe->synth_opts.period;

   __hists__add_entry()
      he.stat.period = sample->period;

   annotated_data_type__update_samples()
      h->period += period;
      h->addr[offset].period += period;

   print_annotated_data_value()
      double percent = h->period ? (100.0 * period / h->period) : 0;

Fix this by defaulting the period to 1 in the ARM SPE auxtrace info
processing path if it is not explicitly specified. This ensures that
downstream tool components can correctly accumulate periods and compute
event percentages for all synthesized SPE events.

With this fix applied, the result is as follows:

Annotate type: 'struct mmu_gather_batch' in [kernel.kallsyms] (15 samples):
============================================================================
 Percent     offset       size  field
  100.00          0       0x10  struct mmu_gather_batch  {
   86.67          0        0x8      struct mmu_gather_batch*    next;
   13.33        0x8        0x4      unsigned int        nr;
    0.00        0xc        0x4      unsigned int        max;
    0.00       0x10          0      struct encoded_page*[]      encoded_pages;
                                };

Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
---
 tools/perf/util/arm-spe.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
index ae7a5e9c3892..7805a1a98a89 100644
--- a/tools/perf/util/arm-spe.c
+++ b/tools/perf/util/arm-spe.c
@@ -2043,6 +2043,17 @@ int arm_spe_process_auxtrace_info(union perf_event *event,
 		err = -EINVAL;
 		goto err_free_queues;
 	}
+
+	/*
+	 * When --itrace is used with non-i/y options (e.g., --itrace=M),
+	 * the period remains 0 because the parser does not apply a default
+	 * for those paths. However, synthesized SPE events such as memory
+	 * accesses, TLB walks, and cache misses still require a valid
+	 * sample->period to correctly accumulate periods and compute event
+	 * percentages. Set it to 1 to ensure proper accounting.
+	 */
+	spe->synth_opts.period = spe->synth_opts.period ?: 1;
+
 	if (spe->synth_opts.period > 1)
 		ui__warning("Arm SPE has a hardware-based sampling period.\n\n"
 			    "--itrace periods > 1i downsample by an interval of n SPE samples rather than n instructions.\n");
-- 
2.34.1