perf intel-pt: Support generating branch stack

Add support for generating branch stack context for PT samples.  The
decoder reports a configurable number of branches as branch context for
each sample. Internally it keeps track of them by using a simple sliding
window.  We also flush the last branch buffer on each sample to avoid
overlapping intervals.

This is useful for:

- Reporting accurate basic block edge frequencies through the perf
  report branch view
- Using with --branch-history to get the wider context of samples
- Other users of LBRs

Also the Documentation is updated.

Examples:

	Record with Intel PT:

		perf record -e intel_pt//u ls

	Branch stacks are used by default if synthesized so:

		perf report --itrace=ile

	is the same as:

		perf report --itrace=ile -b

	Branch history can be requested also:

		perf report --itrace=igle --branch-history

Based-on-patch-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1443186956-18718-15-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 115 insertions, 0 deletions

diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
index 2c01e723826a..05e8fcc5188b 100644
--- a/tools/perf/util/intel-pt.c
+++ b/tools/perf/util/intel-pt.c
@@ -22,6 +22,7 @@
 #include "../perf.h"
 #include "session.h"
 #include "machine.h"
+#include "sort.h"
 #include "tool.h"
 #include "event.h"
 #include "evlist.h"
@@ -115,6 +116,9 @@ struct intel_pt_queue {
         void *decoder;
         const struct intel_pt_state *state;
         struct ip_callchain *chain;
+        struct branch_stack *last_branch;
+        struct branch_stack *last_branch_rb;
+        size_t last_branch_pos;
         union perf_event *event_buf;
         bool on_heap;
         bool stop;
@@ -675,6 +679,19 @@ static struct intel_pt_queue *intel_pt_alloc_queue(struct intel_pt *pt,
                         goto out_free;
         }
 
+        if (pt->synth_opts.last_branch) {
+                size_t sz = sizeof(struct branch_stack);
+
+                sz += pt->synth_opts.last_branch_sz *
+                      sizeof(struct branch_entry);
+                ptq->last_branch = zalloc(sz);
+                if (!ptq->last_branch)
+                        goto out_free;
+                ptq->last_branch_rb = zalloc(sz);
+                if (!ptq->last_branch_rb)
+                        goto out_free;
+        }
+
         ptq->event_buf = malloc(PERF_SAMPLE_MAX_SIZE);
         if (!ptq->event_buf)
                 goto out_free;
@@ -732,6 +749,8 @@ static struct intel_pt_queue *intel_pt_alloc_queue(struct intel_pt *pt,
 
 out_free:
         zfree(&ptq->event_buf);
+        zfree(&ptq->last_branch);
+        zfree(&ptq->last_branch_rb);
         zfree(&ptq->chain);
         free(ptq);
         return NULL;
@@ -746,6 +765,8 @@ static void intel_pt_free_queue(void *priv)
         thread__zput(ptq->thread);
         intel_pt_decoder_free(ptq->decoder);
         zfree(&ptq->event_buf);
+        zfree(&ptq->last_branch);
+        zfree(&ptq->last_branch_rb);
         zfree(&ptq->chain);
         free(ptq);
 }
@@ -876,6 +897,57 @@ static int intel_pt_setup_queues(struct intel_pt *pt)
         return 0;
 }
 
+static inline void intel_pt_copy_last_branch_rb(struct intel_pt_queue *ptq)
+{
+        struct branch_stack *bs_src = ptq->last_branch_rb;
+        struct branch_stack *bs_dst = ptq->last_branch;
+        size_t nr = 0;
+
+        bs_dst->nr = bs_src->nr;
+
+        if (!bs_src->nr)
+                return;
+
+        nr = ptq->pt->synth_opts.last_branch_sz - ptq->last_branch_pos;
+        memcpy(&bs_dst->entries[0],
+               &bs_src->entries[ptq->last_branch_pos],
+               sizeof(struct branch_entry) * nr);
+
+        if (bs_src->nr >= ptq->pt->synth_opts.last_branch_sz) {
+                memcpy(&bs_dst->entries[nr],
+                       &bs_src->entries[0],
+                       sizeof(struct branch_entry) * ptq->last_branch_pos);
+        }
+}
+
+static inline void intel_pt_reset_last_branch_rb(struct intel_pt_queue *ptq)
+{
+        ptq->last_branch_pos = 0;
+        ptq->last_branch_rb->nr = 0;
+}
+
+static void intel_pt_update_last_branch_rb(struct intel_pt_queue *ptq)
+{
+        const struct intel_pt_state *state = ptq->state;
+        struct branch_stack *bs = ptq->last_branch_rb;
+        struct branch_entry *be;
+
+        if (!ptq->last_branch_pos)
+                ptq->last_branch_pos = ptq->pt->synth_opts.last_branch_sz;
+
+        ptq->last_branch_pos -= 1;
+
+        be              = &bs->entries[ptq->last_branch_pos];
+        be->from        = state->from_ip;
+        be->to          = state->to_ip;
+        be->flags.abort = !!(state->flags & INTEL_PT_ABORT_TX);
+        be->flags.in_tx = !!(state->flags & INTEL_PT_IN_TX);
+        /* No support for mispredict */
+
+        if (bs->nr < ptq->pt->synth_opts.last_branch_sz)
+                bs->nr += 1;
+}
+
 static int intel_pt_inject_event(union perf_event *event,
                                  struct perf_sample *sample, u64 type,
                                  bool swapped)
@@ -890,6 +962,10 @@ static int intel_pt_synth_branch_sample(struct intel_pt_queue *ptq)
         struct intel_pt *pt = ptq->pt;
         union perf_event *event = ptq->event_buf;
         struct perf_sample sample = { .ip = 0, };
+        struct dummy_branch_stack {
+                u64                     nr;
+                struct branch_entry     entries;
+        } dummy_bs;
 
         if (pt->branches_filter && !(pt->branches_filter & ptq->flags))
                 return 0;
@@ -912,6 +988,21 @@ static int intel_pt_synth_branch_sample(struct intel_pt_queue *ptq)
         sample.flags = ptq->flags;
         sample.insn_len = ptq->insn_len;
 
+        /*
+         * perf report cannot handle events without a branch stack when using
+         * SORT_MODE__BRANCH so make a dummy one.
+         */
+        if (pt->synth_opts.last_branch && sort__mode == SORT_MODE__BRANCH) {
+                dummy_bs = (struct dummy_branch_stack){
+                        .nr = 1,
+                        .entries = {
+                                .from = sample.ip,
+                                .to = sample.addr,
+                        },
+                };
+                sample.branch_stack = (struct branch_stack *)&dummy_bs;
+        }
+
         if (pt->synth_opts.inject) {
                 ret = intel_pt_inject_event(event, &sample,
                                             pt->branches_sample_type,
@@ -961,6 +1052,11 @@ static int intel_pt_synth_instruction_sample(struct intel_pt_queue *ptq)
                 sample.callchain = ptq->chain;
         }
 
+        if (pt->synth_opts.last_branch) {
+                intel_pt_copy_last_branch_rb(ptq);
+                sample.branch_stack = ptq->last_branch;
+        }
+
         if (pt->synth_opts.inject) {
                 ret = intel_pt_inject_event(event, &sample,
                                             pt->instructions_sample_type,
@@ -974,6 +1070,9 @@ static int intel_pt_synth_instruction_sample(struct intel_pt_queue *ptq)
                 pr_err("Intel Processor Trace: failed to deliver instruction event, error %d\n",
                        ret);
 
+        if (pt->synth_opts.last_branch)
+                intel_pt_reset_last_branch_rb(ptq);
+
         return ret;
 }
 
@@ -1008,6 +1107,11 @@ static int intel_pt_synth_transaction_sample(struct intel_pt_queue *ptq)
                 sample.callchain = ptq->chain;
         }
 
+        if (pt->synth_opts.last_branch) {
+                intel_pt_copy_last_branch_rb(ptq);
+                sample.branch_stack = ptq->last_branch;
+        }
+
         if (pt->synth_opts.inject) {
                 ret = intel_pt_inject_event(event, &sample,
                                             pt->transactions_sample_type,
@@ -1021,6 +1125,9 @@ static int intel_pt_synth_transaction_sample(struct intel_pt_queue *ptq)
                 pr_err("Intel Processor Trace: failed to deliver transaction event, error %d\n",
                        ret);
 
+        if (pt->synth_opts.callchain)
+                intel_pt_reset_last_branch_rb(ptq);
+
         return ret;
 }
 
@@ -1116,6 +1223,9 @@ static int intel_pt_sample(struct intel_pt_queue *ptq)
                         return err;
         }
 
+        if (pt->synth_opts.last_branch)
+                intel_pt_update_last_branch_rb(ptq);
+
         if (!pt->sync_switch)
                 return 0;
 
@@ -1763,6 +1873,8 @@ static int intel_pt_synth_events(struct intel_pt *pt,
                 pt->instructions_sample_period = attr.sample_period;
                 if (pt->synth_opts.callchain)
                         attr.sample_type |= PERF_SAMPLE_CALLCHAIN;
+                if (pt->synth_opts.last_branch)
+                        attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
                 pr_debug("Synthesizing 'instructions' event with id %" PRIu64 " sample type %#" PRIx64 "\n",
                          id, (u64)attr.sample_type);
                 err = intel_pt_synth_event(session, &attr, id);
@@ -1782,6 +1894,8 @@ static int intel_pt_synth_events(struct intel_pt *pt,
                 attr.sample_period = 1;
                 if (pt->synth_opts.callchain)
                         attr.sample_type |= PERF_SAMPLE_CALLCHAIN;
+                if (pt->synth_opts.last_branch)
+                        attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
                 pr_debug("Synthesizing 'transactions' event with id %" PRIu64 " sample type %#" PRIx64 "\n",
                          id, (u64)attr.sample_type);
                 err = intel_pt_synth_event(session, &attr, id);
@@ -1808,6 +1922,7 @@ static int intel_pt_synth_events(struct intel_pt *pt,
                 attr.sample_period = 1;
                 attr.sample_type |= PERF_SAMPLE_ADDR;
                 attr.sample_type &= ~(u64)PERF_SAMPLE_CALLCHAIN;
+                attr.sample_type &= ~(u64)PERF_SAMPLE_BRANCH_STACK;
                 pr_debug("Synthesizing 'branches' event with id %" PRIu64 " sample type %#" PRIx64 "\n",
                          id, (u64)attr.sample_type);
                 err = intel_pt_synth_event(session, &attr, id);