perf hist: Introduce hists class and move lots of methods to it

In cbbc79a we introduced support for multiple events by introducing a
new "event_stat_id" struct and then made several perf_session methods
receive a point to it instead of a pointer to perf_session, and kept the
event_stats and hists rb_tree in perf_session.

While working on the new newt based browser, I realised that it would be
better to introduce a new class, "hists" (short for "histograms"),
renaming the "event_stat_id" struct and the perf_session methods that
were really "hists" methods, as they manipulate only struct hists
members, not touching anything in the other perf_session members.

Other optimizations, such as calculating the maximum lenght of a symbol
name present in an hists instance will be possible as we add them,
avoiding a re-traversal just for finding that information.

The rationale for the name "hists" to replace "event_stat_id" is that we
may have multiple sets of hists for the same event_stat id, as, for
instance, the 'perf diff' tool has, so event stat id is not what
characterizes what this struct and the functions that manipulate it do.

Cc: Eric B Munson <ebmunson@us.ibm.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

10 files changed, 146 insertions, 164 deletions

diff --git a/tools/perf/builtin-annotate.c b/tools/perf/builtin-annotate.c
index c7ac45a59ed5..3940964161b3 100644
--- a/tools/perf/builtin-annotate.c
+++ b/tools/perf/builtin-annotate.c
@@ -96,8 +96,7 @@ static int annotate__hist_hit(struct hist_entry *he, u64 ip)
         return 0;
 }
 
-static int perf_session__add_hist_entry(struct perf_session *self,
-                                        struct addr_location *al)
+static int hists__add_entry(struct hists *self, struct addr_location *al)
 {
         struct hist_entry *he;
 
@@ -112,7 +111,7 @@ static int perf_session__add_hist_entry(struct perf_session *self,
                 return 0;
         }
 
-        he = __perf_session__add_hist_entry(&self->hists, al, NULL, 1);
+        he = __hists__add_entry(self, al, NULL, 1);
         if (he == NULL)
                 return -ENOMEM;
 
@@ -132,7 +131,7 @@ static int process_sample_event(event_t *event, struct perf_session *session)
                 return -1;
         }
 
-        if (!al.filtered && perf_session__add_hist_entry(session, &al)) {
+        if (!al.filtered && hists__add_entry(&session->hists, &al)) {
                 pr_warning("problem incrementing symbol count, "
                            "skipping event\n");
                 return -1;
@@ -514,11 +513,11 @@ static void annotate_sym(struct hist_entry *he)
                 free_source_line(he, len);
 }
 
-static void perf_session__find_annotations(struct perf_session *self)
+static void hists__find_annotations(struct hists *self)
 {
         struct rb_node *nd;
 
-        for (nd = rb_first(&self->hists); nd; nd = rb_next(nd)) {
+        for (nd = rb_first(&self->entries); nd; nd = rb_next(nd)) {
                 struct hist_entry *he = rb_entry(nd, struct hist_entry, rb_node);
                 struct sym_priv *priv;
 
@@ -570,9 +569,9 @@ static int __cmd_annotate(void)
         if (verbose > 2)
                 perf_session__fprintf_dsos(session, stdout);
 
-        perf_session__collapse_resort(&session->hists);
-        perf_session__output_resort(&session->hists, session->event_total[0]);
-        perf_session__find_annotations(session);
+        hists__collapse_resort(&session->hists);
+        hists__output_resort(&session->hists);
+        hists__find_annotations(&session->hists);
 out_delete:
         perf_session__delete(session);
 
diff --git a/tools/perf/builtin-diff.c b/tools/perf/builtin-diff.c
index 613a5c4f6d83..3a95a0260a5b 100644
--- a/tools/perf/builtin-diff.c
+++ b/tools/perf/builtin-diff.c
@@ -22,10 +22,10 @@ static char	  diff__default_sort_order[] = "dso,symbol";
 static bool  force;
 static bool show_displacement;
 
-static int perf_session__add_hist_entry(struct perf_session *self,
-                                        struct addr_location *al, u64 count)
+static int hists__add_entry(struct hists *self,
+                            struct addr_location *al, u64 count)
 {
-        if (__perf_session__add_hist_entry(&self->hists, al, NULL, count) != NULL)
+        if (__hists__add_entry(self, al, NULL, count) != NULL)
                 return 0;
         return -ENOMEM;
 }
@@ -49,12 +49,12 @@ static int diff__process_sample_event(event_t *event, struct perf_session *sessi
 
         event__parse_sample(event, session->sample_type, &data);
 
-        if (perf_session__add_hist_entry(session, &al, data.period)) {
+        if (hists__add_entry(&session->hists, &al, data.period)) {
                 pr_warning("problem incrementing symbol count, skipping event\n");
                 return -1;
         }
 
-        session->events_stats.total += data.period;
+        session->hists.stats.total += data.period;
         return 0;
 }
 
@@ -87,35 +87,34 @@ static void perf_session__insert_hist_entry_by_name(struct rb_root *root,
         rb_insert_color(&he->rb_node, root);
 }
 
-static void perf_session__resort_hist_entries(struct perf_session *self)
+static void hists__resort_entries(struct hists *self)
 {
         unsigned long position = 1;
         struct rb_root tmp = RB_ROOT;
-        struct rb_node *next = rb_first(&self->hists);
+        struct rb_node *next = rb_first(&self->entries);
 
         while (next != NULL) {
                 struct hist_entry *n = rb_entry(next, struct hist_entry, rb_node);
 
                 next = rb_next(&n->rb_node);
-                rb_erase(&n->rb_node, &self->hists);
+                rb_erase(&n->rb_node, &self->entries);
                 n->position = position++;
                 perf_session__insert_hist_entry_by_name(&tmp, n);
         }
 
-        self->hists = tmp;
+        self->entries = tmp;
 }
 
-static void perf_session__set_hist_entries_positions(struct perf_session *self)
+static void hists__set_positions(struct hists *self)
 {
-        perf_session__output_resort(&self->hists, self->events_stats.total);
-        perf_session__resort_hist_entries(self);
+        hists__output_resort(self);
+        hists__resort_entries(self);
 }
 
-static struct hist_entry *
-perf_session__find_hist_entry(struct perf_session *self,
-                              struct hist_entry *he)
+static struct hist_entry *hists__find_entry(struct hists *self,
+                                            struct hist_entry *he)
 {
-        struct rb_node *n = self->hists.rb_node;
+        struct rb_node *n = self->entries.rb_node;
 
         while (n) {
                 struct hist_entry *iter = rb_entry(n, struct hist_entry, rb_node);
@@ -132,14 +131,13 @@ perf_session__find_hist_entry(struct perf_session *self,
         return NULL;
 }
 
-static void perf_session__match_hists(struct perf_session *old_session,
-                                      struct perf_session *new_session)
+static void hists__match(struct hists *older, struct hists *newer)
 {
         struct rb_node *nd;
 
-        for (nd = rb_first(&new_session->hists); nd; nd = rb_next(nd)) {
+        for (nd = rb_first(&newer->entries); nd; nd = rb_next(nd)) {
                 struct hist_entry *pos = rb_entry(nd, struct hist_entry, rb_node);
-                pos->pair = perf_session__find_hist_entry(old_session, pos);
+                pos->pair = hists__find_entry(older, pos);
         }
 }
 
@@ -159,15 +157,13 @@ static int __cmd_diff(void)
                         goto out_delete;
         }
 
-        perf_session__output_resort(&session[1]->hists,
-                                    session[1]->events_stats.total);
+        hists__output_resort(&session[1]->hists);
         if (show_displacement)
-                perf_session__set_hist_entries_positions(session[0]);
+                hists__set_positions(&session[0]->hists);
 
-        perf_session__match_hists(session[0], session[1]);
-        perf_session__fprintf_hists(&session[1]->hists, session[0],
-                                    show_displacement, stdout,
-                                    session[1]->events_stats.total);
+        hists__match(&session[0]->hists, &session[1]->hists);
+        hists__fprintf(&session[1]->hists, &session[0]->hists,
+                       show_displacement, stdout);
 out_delete:
         for (i = 0; i < 2; ++i)
                 perf_session__delete(session[i]);
diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 642a6d8eb5dc..53077fd973f0 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -44,16 +44,17 @@ static char		*pretty_printing_style = default_pretty_printing_style;
 
 static char             callchain_default_opt[] = "fractal,0.5";
 
-static struct event_stat_id *get_stats(struct perf_session *self,
-                                       u64 event_stream, u32 type, u64 config)
+static struct hists *perf_session__hists_findnew(struct perf_session *self,
+                                                 u64 event_stream, u32 type,
+                                                 u64 config)
 {
-        struct rb_node **p = &self->stats_by_id.rb_node;
+        struct rb_node **p = &self->hists_tree.rb_node;
         struct rb_node *parent = NULL;
-        struct event_stat_id *iter, *new;
+        struct hists *iter, *new;
 
         while (*p != NULL) {
                 parent = *p;
-                iter = rb_entry(parent, struct event_stat_id, rb_node);
+                iter = rb_entry(parent, struct hists, rb_node);
                 if (iter->config == config)
                         return iter;
 
@@ -64,15 +65,15 @@ static struct event_stat_id *get_stats(struct perf_session *self,
                         p = &(*p)->rb_left;
         }
 
-        new = malloc(sizeof(struct event_stat_id));
+        new = malloc(sizeof(struct hists));
         if (new == NULL)
                 return NULL;
-        memset(new, 0, sizeof(struct event_stat_id));
+        memset(new, 0, sizeof(struct hists));
         new->event_stream = event_stream;
         new->config = config;
         new->type = type;
         rb_link_node(&new->rb_node, parent, p);
-        rb_insert_color(&new->rb_node, &self->stats_by_id);
+        rb_insert_color(&new->rb_node, &self->hists_tree);
         return new;
 }
 
@@ -84,7 +85,7 @@ static int perf_session__add_hist_entry(struct perf_session *self,
         struct symbol *parent = NULL;
         int err = -ENOMEM;
         struct hist_entry *he;
-        struct event_stat_id *stats;
+        struct hists *hists;
         struct perf_event_attr *attr;
 
         if ((sort__has_parent || symbol_conf.use_callchain) && data->callchain) {
@@ -96,13 +97,12 @@ static int perf_session__add_hist_entry(struct perf_session *self,
 
         attr = perf_header__find_attr(data->id, &self->header);
         if (attr)
-                stats = get_stats(self, data->id, attr->type, attr->config);
+                hists = perf_session__hists_findnew(self, data->id, attr->type, attr->config);
         else
-                stats = get_stats(self, data->id, 0, 0);
-        if (stats == NULL)
+                hists = perf_session__hists_findnew(self, data->id, 0, 0);
+        if (hists == NULL)
                 goto out_free_syms;
-        he = __perf_session__add_hist_entry(&stats->hists, al, parent,
-                                            data->period);
+        he = __hists__add_entry(hists, al, parent, data->period);
         if (he == NULL)
                 goto out_free_syms;
         err = 0;
@@ -117,18 +117,19 @@ static int add_event_total(struct perf_session *session,
                            struct sample_data *data,
                            struct perf_event_attr *attr)
 {
-        struct event_stat_id *stats;
+        struct hists *hists;
 
         if (attr)
-                stats = get_stats(session, data->id, attr->type, attr->config);
+                hists = perf_session__hists_findnew(session, data->id,
+                                                    attr->type, attr->config);
         else
-                stats = get_stats(session, data->id, 0, 0);
+                hists = perf_session__hists_findnew(session, data->id, 0, 0);
 
-        if (!stats)
+        if (!hists)
                 return -ENOMEM;
 
-        stats->stats.total += data->period;
-        session->events_stats.total += data->period;
+        hists->stats.total += data->period;
+        session->hists.stats.total += data->period;
         return 0;
 }
 
@@ -292,35 +293,33 @@ static int __cmd_report(void)
         if (verbose > 2)
                 perf_session__fprintf_dsos(session, stdout);
 
-        next = rb_first(&session->stats_by_id);
+        next = rb_first(&session->hists_tree);
         while (next) {
-                struct event_stat_id *stats;
+                struct hists *hists;
                 u64 nr_hists;
 
-                stats = rb_entry(next, struct event_stat_id, rb_node);
-                perf_session__collapse_resort(&stats->hists);
-                nr_hists = perf_session__output_resort(&stats->hists,
-                                                       stats->stats.total);
+                hists = rb_entry(next, struct hists, rb_node);
+                hists__collapse_resort(hists);
+                nr_hists = hists__output_resort(hists);
                 if (use_browser)
-                        perf_session__browse_hists(&stats->hists, nr_hists,
-                                                   stats->stats.total, help,
+                        perf_session__browse_hists(&hists->entries, nr_hists,
+                                                   hists->stats.total, help,
                                                    input_name);
                 else {
-                        if (rb_first(&session->stats_by_id) ==
-                            rb_last(&session->stats_by_id))
+                        if (rb_first(&session->hists.entries) ==
+                            rb_last(&session->hists.entries))
                                 fprintf(stdout, "# Samples: %Ld\n#\n",
-                                        stats->stats.total);
+                                        hists->stats.total);
                         else
                                 fprintf(stdout, "# Samples: %Ld %s\n#\n",
-                                        stats->stats.total,
-                                        __event_name(stats->type, stats->config));
+                                        hists->stats.total,
+                                        __event_name(hists->type, hists->config));
 
-                        perf_session__fprintf_hists(&stats->hists, NULL, false, stdout,
-                                            stats->stats.total);
+                        hists__fprintf(hists, NULL, false, stdout);
                         fprintf(stdout, "\n\n");
                 }
 
-                next = rb_next(&stats->rb_node);
+                next = rb_next(&hists->rb_node);
         }
 
         if (!use_browser && sort_order == default_sort_order &&
diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 9c483e92e8db..6e268ca761e9 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -107,7 +107,7 @@ static int process_sample_event(event_t *event, struct perf_session *session)
                                              data.time, thread->comm);
         }
 
-        session->events_stats.total += data.period;
+        session->hists.stats.total += data.period;
         return 0;
 }
 
diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index d2ea9dd9fdf1..cce006ec8f05 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -368,7 +368,7 @@ int event__process_comm(event_t *self, struct perf_session *session)
 int event__process_lost(event_t *self, struct perf_session *session)
 {
         dump_printf(": id:%Ld: lost:%Ld\n", self->lost.id, self->lost.lost);
-        session->events_stats.lost += self->lost.lost;
+        session->hists.stats.lost += self->lost.lost;
         return 0;
 }
 
diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
index 6cc1b1dced55..48c2cc9dae4f 100644
--- a/tools/perf/util/event.h
+++ b/tools/perf/util/event.h
@@ -131,20 +131,6 @@ typedef union event_union {
         struct build_id_event           build_id;
 } event_t;
 
-struct events_stats {
-        u64 total;
-        u64 lost;
-};
-
-struct event_stat_id {
-        struct rb_node          rb_node;
-        struct rb_root          hists;
-        struct events_stats     stats;
-        u64                     config;
-        u64                     event_stream;
-        u32                     type;
-};
-
 void event__print_totals(void);
 
 struct perf_session;
diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index 0f154a530dfd..410cf56c9662 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -8,21 +8,21 @@ struct callchain_param	callchain_param = {
         .min_percent = 0.5
 };
 
-static void perf_session__add_cpumode_count(struct hist_entry *he,
-                                            unsigned int cpumode, u64 count)
+static void hist_entry__add_cpumode_count(struct hist_entry *self,
+                                          unsigned int cpumode, u64 count)
 {
         switch (cpumode) {
         case PERF_RECORD_MISC_KERNEL:
-                he->count_sys += count;
+                self->count_sys += count;
                 break;
         case PERF_RECORD_MISC_USER:
-                he->count_us += count;
+                self->count_us += count;
                 break;
         case PERF_RECORD_MISC_GUEST_KERNEL:
-                he->count_guest_sys += count;
+                self->count_guest_sys += count;
                 break;
         case PERF_RECORD_MISC_GUEST_USER:
-                he->count_guest_us += count;
+                self->count_guest_us += count;
                 break;
         default:
                 break;
@@ -47,12 +47,11 @@ static struct hist_entry *hist_entry__new(struct hist_entry *template)
         return self;
 }
 
-struct hist_entry *__perf_session__add_hist_entry(struct rb_root *hists,
-                                                  struct addr_location *al,
-                                                  struct symbol *sym_parent,
-                                                  u64 count)
+struct hist_entry *__hists__add_entry(struct hists *self,
+                                      struct addr_location *al,
+                                      struct symbol *sym_parent, u64 count)
 {
-        struct rb_node **p = &hists->rb_node;
+        struct rb_node **p = &self->entries.rb_node;
         struct rb_node *parent = NULL;
         struct hist_entry *he;
         struct hist_entry entry = {
@@ -89,9 +88,9 @@ struct hist_entry *__perf_session__add_hist_entry(struct rb_root *hists,
         if (!he)
                 return NULL;
         rb_link_node(&he->rb_node, parent, p);
-        rb_insert_color(&he->rb_node, hists);
+        rb_insert_color(&he->rb_node, &self->entries);
 out:
-        perf_session__add_cpumode_count(he, al->cpumode, count);
+        hist_entry__add_cpumode_count(he, al->cpumode, count);
         return he;
 }
 
@@ -167,7 +166,7 @@ static void collapse__insert_entry(struct rb_root *root, struct hist_entry *he)
         rb_insert_color(&he->rb_node, root);
 }
 
-void perf_session__collapse_resort(struct rb_root *hists)
+void hists__collapse_resort(struct hists *self)
 {
         struct rb_root tmp;
         struct rb_node *next;
@@ -177,28 +176,28 @@ void perf_session__collapse_resort(struct rb_root *hists)
                 return;
 
         tmp = RB_ROOT;
-        next = rb_first(hists);
+        next = rb_first(&self->entries);
 
         while (next) {
                 n = rb_entry(next, struct hist_entry, rb_node);
                 next = rb_next(&n->rb_node);
 
-                rb_erase(&n->rb_node, hists);
+                rb_erase(&n->rb_node, &self->entries);
                 collapse__insert_entry(&tmp, n);
         }
 
-        *hists = tmp;
+        self->entries = tmp;
 }
 
 /*
  * reverse the map, sort on count.
  */
 
-static void perf_session__insert_output_hist_entry(struct rb_root *root,
-                                                   struct hist_entry *he,
-                                                   u64 min_callchain_hits)
+static void __hists__insert_output_entry(struct rb_root *entries,
+                                         struct hist_entry *he,
+                                         u64 min_callchain_hits)
 {
-        struct rb_node **p = &root->rb_node;
+        struct rb_node **p = &entries->rb_node;
         struct rb_node *parent = NULL;
         struct hist_entry *iter;
 
@@ -217,10 +216,10 @@ static void perf_session__insert_output_hist_entry(struct rb_root *root,
         }
 
         rb_link_node(&he->rb_node, parent, p);
-        rb_insert_color(&he->rb_node, root);
+        rb_insert_color(&he->rb_node, entries);
 }
 
-u64 perf_session__output_resort(struct rb_root *hists, u64 total_samples)
+u64 hists__output_resort(struct hists *self)
 {
         struct rb_root tmp;
         struct rb_node *next;
@@ -228,23 +227,21 @@ u64 perf_session__output_resort(struct rb_root *hists, u64 total_samples)
         u64 min_callchain_hits;
         u64 nr_hists = 0;
 
-        min_callchain_hits =
-                total_samples * (callchain_param.min_percent / 100);
+        min_callchain_hits = self->stats.total * (callchain_param.min_percent / 100);
 
         tmp = RB_ROOT;
-        next = rb_first(hists);
+        next = rb_first(&self->entries);
 
         while (next) {
                 n = rb_entry(next, struct hist_entry, rb_node);
                 next = rb_next(&n->rb_node);
 
-                rb_erase(&n->rb_node, hists);
-                perf_session__insert_output_hist_entry(&tmp, n,
-                                                       min_callchain_hits);
+                rb_erase(&n->rb_node, &self->entries);
+                __hists__insert_output_entry(&tmp, n, min_callchain_hits);
                 ++nr_hists;
         }
 
-        *hists = tmp;
+        self->entries = tmp;
         return nr_hists;
 }
 
@@ -500,12 +497,9 @@ static size_t hist_entry_callchain__fprintf(FILE *fp, struct hist_entry *self,
         return ret;
 }
 
-int hist_entry__snprintf(struct hist_entry *self,
-                           char *s, size_t size,
-                           struct perf_session *pair_session,
-                           bool show_displacement,
-                           long displacement, bool color,
-                           u64 session_total)
+int hist_entry__snprintf(struct hist_entry *self, char *s, size_t size,
+                         struct hists *pair_hists, bool show_displacement,
+                         long displacement, bool color, u64 session_total)
 {
         struct sort_entry *se;
         u64 count, total, count_sys, count_us, count_guest_sys, count_guest_us;
@@ -515,9 +509,9 @@ int hist_entry__snprintf(struct hist_entry *self,
         if (symbol_conf.exclude_other && !self->parent)
                 return 0;
 
-        if (pair_session) {
+        if (pair_hists) {
                 count = self->pair ? self->pair->count : 0;
-                total = pair_session->events_stats.total;
+                total = pair_hists->stats.total;
                 count_sys = self->pair ? self->pair->count_sys : 0;
                 count_us = self->pair ? self->pair->count_us : 0;
                 count_guest_sys = self->pair ? self->pair->count_guest_sys : 0;
@@ -569,7 +563,7 @@ int hist_entry__snprintf(struct hist_entry *self,
                         ret += snprintf(s + ret, size - ret, "%11lld", count);
         }
 
-        if (pair_session) {
+        if (pair_hists) {
                 char bf[32];
                 double old_percent = 0, new_percent = 0, diff;
 
@@ -615,14 +609,12 @@ int hist_entry__snprintf(struct hist_entry *self,
         return ret;
 }
 
-int hist_entry__fprintf(struct hist_entry *self,
-                        struct perf_session *pair_session,
-                        bool show_displacement,
-                        long displacement, FILE *fp,
+int hist_entry__fprintf(struct hist_entry *self, struct hists *pair_hists,
+                        bool show_displacement, long displacement, FILE *fp,
                         u64 session_total)
 {
         char bf[512];
-        hist_entry__snprintf(self, bf, sizeof(bf), pair_session,
+        hist_entry__snprintf(self, bf, sizeof(bf), pair_hists,
                              show_displacement, displacement,
                              true, session_total);
         return fprintf(fp, "%s\n", bf);
@@ -644,10 +636,8 @@ static size_t hist_entry__fprintf_callchain(struct hist_entry *self, FILE *fp,
                                              left_margin);
 }
 
-size_t perf_session__fprintf_hists(struct rb_root *hists,
-                                   struct perf_session *pair,
-                                   bool show_displacement, FILE *fp,
-                                   u64 session_total)
+size_t hists__fprintf(struct hists *self, struct hists *pair,
+                      bool show_displacement, FILE *fp)
 {
         struct sort_entry *se;
         struct rb_node *nd;
@@ -753,7 +743,7 @@ size_t perf_session__fprintf_hists(struct rb_root *hists,
         fprintf(fp, "\n#\n");
 
 print_entries:
-        for (nd = rb_first(hists); nd; nd = rb_next(nd)) {
+        for (nd = rb_first(&self->entries); nd; nd = rb_next(nd)) {
                 struct hist_entry *h = rb_entry(nd, struct hist_entry, rb_node);
 
                 if (show_displacement) {
@@ -765,10 +755,10 @@ print_entries:
                         ++position;
                 }
                 ret += hist_entry__fprintf(h, pair, show_displacement,
-                                           displacement, fp, session_total);
+                                           displacement, fp, self->stats.total);
 
                 if (symbol_conf.use_callchain)
-                        ret += hist_entry__fprintf_callchain(h, fp, session_total);
+                        ret += hist_entry__fprintf_callchain(h, fp, self->stats.total);
 
                 if (h->ms.map == NULL && verbose > 1) {
                         __map_groups__fprintf_maps(&h->thread->mg,
diff --git a/tools/perf/util/hist.h b/tools/perf/util/hist.h
index b49013adb34b..bdde81eca69f 100644
--- a/tools/perf/util/hist.h
+++ b/tools/perf/util/hist.h
@@ -6,34 +6,40 @@
 
 extern struct callchain_param callchain_param;
 
-struct perf_session;
 struct hist_entry;
 struct addr_location;
 struct symbol;
 struct rb_root;
 
-struct hist_entry *__perf_session__add_hist_entry(struct rb_root *hists,
-                                                  struct addr_location *al,
-                                                  struct symbol *parent,
-                                                  u64 count);
+struct events_stats {
+        u64 total;
+        u64 lost;
+};
+
+struct hists {
+        struct rb_node          rb_node;
+        struct rb_root          entries;
+        struct events_stats     stats;
+        u64                     config;
+        u64                     event_stream;
+        u32                     type;
+};
+
+struct hist_entry *__hists__add_entry(struct hists *self,
+                                      struct addr_location *al,
+                                      struct symbol *parent, u64 count);
 extern int64_t hist_entry__cmp(struct hist_entry *, struct hist_entry *);
 extern int64_t hist_entry__collapse(struct hist_entry *, struct hist_entry *);
-int hist_entry__fprintf(struct hist_entry *self,
-                           struct perf_session *pair_session,
-                           bool show_displacement,
-                           long displacement, FILE *fp,
-                           u64 session_total);
-int hist_entry__snprintf(struct hist_entry *self,
-                         char *bf, size_t size,
-                         struct perf_session *pair_session,
-                         bool show_displacement, long displacement,
-                         bool color, u64 session_total);
+int hist_entry__fprintf(struct hist_entry *self, struct hists *pair_hists,
+                        bool show_displacement, long displacement, FILE *fp,
+                        u64 total);
+int hist_entry__snprintf(struct hist_entry *self, char *bf, size_t size,
+                         struct hists *pair_hists, bool show_displacement,
+                         long displacement, bool color, u64 total);
 void hist_entry__free(struct hist_entry *);
 
-u64 perf_session__output_resort(struct rb_root *hists, u64 total_samples);
-void perf_session__collapse_resort(struct rb_root *hists);
-size_t perf_session__fprintf_hists(struct rb_root *hists,
-                                   struct perf_session *pair,
-                                   bool show_displacement, FILE *fp,
-                                   u64 session_total);
+u64 hists__output_resort(struct hists *self);
+void hists__collapse_resort(struct hists *self);
+size_t hists__fprintf(struct hists *self, struct hists *pair,
+                      bool show_displacement, FILE *fp);
 #endif  /* __PERF_HIST_H */
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 4130036a0109..72a7f6ae0293 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -89,7 +89,7 @@ struct perf_session *perf_session__new(const char *filename, int mode, bool forc
 
         memcpy(self->filename, filename, len);
         self->threads = RB_ROOT;
-        self->stats_by_id = RB_ROOT;
+        self->hists_tree = RB_ROOT;
         self->last_match = NULL;
         self->mmap_window = 32;
         self->cwd = NULL;
diff --git a/tools/perf/util/session.h b/tools/perf/util/session.h
index 242d528bfae2..46190f94b547 100644
--- a/tools/perf/util/session.h
+++ b/tools/perf/util/session.h
@@ -1,6 +1,7 @@
 #ifndef __PERF_SESSION_H
 #define __PERF_SESSION_H
 
+#include "hist.h"
 #include "event.h"
 #include "header.h"
 #include "symbol.h"
@@ -28,11 +29,16 @@ struct perf_session {
         struct thread           *last_match;
         struct machine          host_machine;
         struct rb_root          machines;
-        struct events_stats     events_stats;
-        struct rb_root          stats_by_id;
+        struct rb_root          hists_tree;
         unsigned long           event_total[PERF_RECORD_MAX];
         unsigned long           unknown_events;
-        struct rb_root          hists;
+        /*
+         * FIXME: should point to the first entry in hists_tree and
+         *        be a hists instance. Right now its only 'report'
+         *        that is using ->hists_tree while all the rest use
+         *        ->hists.
+         */
+        struct hists            hists;
         u64                     sample_type;
         int                     fd;
         bool                    fd_pipe;