perf arm-spe: Add branch stack

Although Arm SPE cannot generate continuous branch records, this commit
creates a branch stack with only one branch entry.  A single branch info
can be used for performance optimization.

A branch stack structure is dynamically allocated in the decode queue.
The branch stack and stack flags are synthesized based on branch types
and associated events.

After:

  # perf script --itrace=bl1 -F flags,addr,brstack

  jcc                   ffffc0fad9c6b214 0xffffc0fad9c6b234/0xffffc0fad9c6b214/P/-/-/7/COND/-
  jcc/miss,not_taken/   ffffc0fadaaebb30 0xffffc0fadaaebb2c/0xffffc0fadaaebb30/MN/-/-/7/COND/-
  jmp                   ffffc0fadaaea358 0xffffc0fadaaea5ec/0xffffc0fadaaea358/P/-/-/5//-
  jcc/not_taken/        ffffc0fadaae6494 0xffffc0fadaae6490/0xffffc0fadaae6494/PN/-/-/11/COND/-
  jcc/not_taken/            ffff7f83ab54 0xffff7f83ab50/0xffff7f83ab54/PN/-/-/13/COND/-
  jcc/not_taken/            ffff7f83ab08 0xffff7f83ab04/0xffff7f83ab08/PN/-/-/8/COND/-
  jcc                       ffff7f83aa80 0xffff7f83aa58/0xffff7f83aa80/P/-/-/10/COND/-
  jcc                       ffff7f9a45d0 0xffff7f9a43f0/0xffff7f9a45d0/P/-/-/29/COND/-
  jcc/not_taken/        ffffc0fad9ba6db4 0xffffc0fad9ba6db0/0xffffc0fad9ba6db4/PN/-/-/44/COND/-
  jcc                   ffffc0fadaac2964 0xffffc0fadaac2970/0xffffc0fadaac2964/P/-/-/6/COND/-
  jcc                   ffffc0fad99ddc10 0xffffc0fad99ddc04/0xffffc0fad99ddc10/P/-/-/72/COND/-
  jcc/not_taken/        ffffc0fad9b3f21c 0xffffc0fad9b3f218/0xffffc0fad9b3f21c/PN/-/-/64/COND/-
  jcc                   ffffc0fad9c3b604 0xffffc0fad9c3b5f8/0xffffc0fad9c3b604/P/-/-/13/COND/-
  jcc                   ffffc0fadaad6048 0xffffc0fadaad5f8c/0xffffc0fadaad6048/P/-/-/5/COND/-
  return/miss/              ffff7f84e614 0xffffc0fad98a2274/0xffff7f84e614/M/-/-/13/RET/-
  jcc/not_taken/        ffffc0fadaac4eb4 0xffffc0fadaac4eb0/0xffffc0fadaac4eb4/PN/-/-/5/COND/-
  jmp                       ffff7f8e3130 0xffff7f87555c/0xffff7f8e3130/P/-/-/5//-
  jcc/not_taken/        ffffc0fad9b3d9b0 0xffffc0fad9b3d9ac/0xffffc0fad9b3d9b0/PN/-/-/14/COND/-
  return                ffffc0fad9b91950 0xffffc0fad98c3e28/0xffffc0fad9b91950/P/-/-/12/RET/-

Reviewed-by: Ian Rogers <irogers@google.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Link: https://lore.kernel.org/r/20250304111240.3378214-12-leo.yan@arm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
index daecf9e1017a9e87488869db528d8c4bf43b20bd..ed89b7dbc244a707d0be8db4b8f608843a13eb24 100644 (file)
--- a/tools/perf/util/arm-spe.c
+++ b/tools/perf/util/arm-spe.c
@@ -103,6 +103,7 @@ struct arm_spe_queue {
        struct thread                   *thread;
        u64                             period_instructions;
        u32                             flags;
+       struct branch_stack             *last_branch;
 };
 
 struct data_source_handle {
@@ -233,6 +234,16 @@ static struct arm_spe_queue *arm_spe__alloc_queue(struct arm_spe *spe,
        params.get_trace = arm_spe_get_trace;
        params.data = speq;
 
+       if (spe->synth_opts.last_branch) {
+               size_t sz = sizeof(struct branch_stack);
+
+               /* Allocate one entry for TGT */
+               sz += sizeof(struct branch_entry);
+               speq->last_branch = zalloc(sz);
+               if (!speq->last_branch)
+                       goto out_free;
+       }
+
        /* create new decoder */
        speq->decoder = arm_spe_decoder_new(&params);
        if (!speq->decoder)
@@ -242,6 +253,7 @@ static struct arm_spe_queue *arm_spe__alloc_queue(struct arm_spe *spe,
 
 out_free:
        zfree(&speq->event_buf);
+       zfree(&speq->last_branch);
        free(speq);
 
        return NULL;
@@ -348,6 +360,73 @@ static void arm_spe_prep_sample(struct arm_spe *spe,
        event->sample.header.size = sizeof(struct perf_event_header);
 }
 
+static void arm_spe__prep_branch_stack(struct arm_spe_queue *speq)
+{
+       struct arm_spe_record *record = &speq->decoder->record;
+       struct branch_stack *bstack = speq->last_branch;
+       struct branch_flags *bs_flags;
+       size_t sz = sizeof(struct branch_stack) +
+                   sizeof(struct branch_entry) /* TGT */;
+
+       /* Clean up branch stack */
+       memset(bstack, 0x0, sz);
+
+       if (!(speq->flags & PERF_IP_FLAG_BRANCH))
+               return;
+
+       bstack->entries[0].from = record->from_ip;
+       bstack->entries[0].to = record->to_ip;
+
+       bs_flags = &bstack->entries[0].flags;
+       bs_flags->value = 0;
+
+       if (record->op & ARM_SPE_OP_BR_CR_BL) {
+               if (record->op & ARM_SPE_OP_BR_COND)
+                       bs_flags->type |= PERF_BR_COND_CALL;
+               else
+                       bs_flags->type |= PERF_BR_CALL;
+       /*
+        * Indirect branch instruction without link (e.g. BR),
+        * take this case as function return.
+        */
+       } else if (record->op & ARM_SPE_OP_BR_CR_RET ||
+                  record->op & ARM_SPE_OP_BR_INDIRECT) {
+               if (record->op & ARM_SPE_OP_BR_COND)
+                       bs_flags->type |= PERF_BR_COND_RET;
+               else
+                       bs_flags->type |= PERF_BR_RET;
+       } else if (record->op & ARM_SPE_OP_BR_CR_NON_BL_RET) {
+               if (record->op & ARM_SPE_OP_BR_COND)
+                       bs_flags->type |= PERF_BR_COND;
+               else
+                       bs_flags->type |= PERF_BR_UNCOND;
+       } else {
+               if (record->op & ARM_SPE_OP_BR_COND)
+                       bs_flags->type |= PERF_BR_COND;
+               else
+                       bs_flags->type |= PERF_BR_UNKNOWN;
+       }
+
+       if (record->type & ARM_SPE_BRANCH_MISS) {
+               bs_flags->mispred = 1;
+               bs_flags->predicted = 0;
+       } else {
+               bs_flags->mispred = 0;
+               bs_flags->predicted = 1;
+       }
+
+       if (record->type & ARM_SPE_BRANCH_NOT_TAKEN)
+               bs_flags->not_taken = 1;
+
+       if (record->type & ARM_SPE_IN_TXN)
+               bs_flags->in_tx = 1;
+
+       bs_flags->cycles = min(record->latency, 0xFFFFU);
+
+       bstack->nr = 1;
+       bstack->hw_idx = -1ULL;
+}
+
 static int arm_spe__inject_event(union perf_event *event, struct perf_sample *sample, u64 type)
 {
        event->header.size = perf_event__sample_event_size(sample, type, 0);
@@ -416,6 +495,7 @@ static int arm_spe__synth_branch_sample(struct arm_spe_queue *speq,
        sample.addr = record->to_ip;
        sample.weight = record->latency;
        sample.flags = speq->flags;
+       sample.branch_stack = speq->last_branch;
 
        ret = arm_spe_deliver_synth_event(spe, speq, event, &sample);
        perf_sample__exit(&sample);
@@ -450,6 +530,7 @@ static int arm_spe__synth_instruction_sample(struct arm_spe_queue *speq,
        sample.period = spe->instructions_sample_period;
        sample.weight = record->latency;
        sample.flags = speq->flags;
+       sample.branch_stack = speq->last_branch;
 
        ret = arm_spe_deliver_synth_event(spe, speq, event, &sample);
        perf_sample__exit(&sample);
@@ -787,6 +868,10 @@ static int arm_spe_sample(struct arm_spe_queue *speq)
                }
        }
 
+       if (spe->synth_opts.last_branch &&
+           (spe->sample_branch || spe->sample_instructions))
+               arm_spe__prep_branch_stack(speq);
+
        if (spe->sample_branch && (record->op & ARM_SPE_OP_BRANCH_ERET)) {
                err = arm_spe__synth_branch_sample(speq, spe->branch_id);
                if (err)
@@ -1278,6 +1363,7 @@ static void arm_spe_free_queue(void *priv)
        thread__zput(speq->thread);
        arm_spe_decoder_free(speq->decoder);
        zfree(&speq->event_buf);
+       zfree(&speq->last_branch);
        free(speq);
 }
 
@@ -1497,6 +1583,19 @@ arm_spe_synth_events(struct arm_spe *spe, struct perf_session *session)
                id += 1;
        }
 
+       if (spe->synth_opts.last_branch) {
+               if (spe->synth_opts.last_branch_sz > 1)
+                       pr_debug("Arm SPE supports only one bstack entry (TGT).\n");
+
+               attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
+               /*
+                * We don't use the hardware index, but the sample generation
+                * code uses the new format branch_stack with this field,
+                * so the event attributes must indicate that it's present.
+                */
+               attr.branch_sample_type |= PERF_SAMPLE_BRANCH_HW_INDEX;
+       }
+
        if (spe->synth_opts.branches) {
                spe->sample_branch = true;