perf symbols: Improve DSO long names lookup speed with rbtree

With workload that spawns and destroys many threads and processes, it
was found that perf-mem could took a long time to post-process the perf
data after the target workload had completed its operation.

The performance bottleneck was found to be the lookup and insertion of
the new DSO structures (thousands of them in this case).

In a dual-socket Ivy-Bridge E7-4890 v2 machine (30-core, 60-thread), the
perf profile below shows what perf was doing after the profiled AIM7
shared workload completed:

-     83.94%  perf  libc-2.11.3.so     [.] __strcmp_sse42
   - __strcmp_sse42
      - 99.82% map__new
           machine__process_mmap_event
           perf_session_deliver_event
           perf_session__process_event
           __perf_session__process_events
           cmd_record
           cmd_mem
           run_builtin
           main
           __libc_start_main
-     13.17%  perf  perf               [.] __dsos__findnew
     __dsos__findnew
     map__new
     machine__process_mmap_event
     perf_session_deliver_event
     perf_session__process_event
     __perf_session__process_events
     cmd_record
     cmd_mem
     run_builtin
     main
     __libc_start_main

So about 97% of CPU times were spent in the map__new() function trying
to insert new DSO entry into the DSO linked list. The whole
post-processing step took about 9 minutes.

The DSO structures are currently searched linearly. So the total
processing time will be proportional to n^2.

To overcome this performance problem, the DSO code is modified to also
put the DSO structures in a RB tree sorted by its long name in
additional to being in a simple linked list. With this change, the
processing time will become proportional to n*log(n) which will be much
quicker for large n. However, the short name will still be searched
using the old linear searching method.  With that patch in place, the
same perf-mem post-processing step took less than 30 seconds to
complete.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott J Norton <scott.norton@hp.com>
Link: http://lkml.kernel.org/r/1412098575-27863-3-git-send-email-Waiman.Long@hp.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

3 files changed, 71 insertions, 5 deletions

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 901a58fa3f22..0247acfdfaca 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -653,6 +653,65 @@ struct dso *dso__kernel_findnew(struct machine *machine, const char *name,
         return dso;
 }
 
+/*
+ * Find a matching entry and/or link current entry to RB tree.
+ * Either one of the dso or name parameter must be non-NULL or the
+ * function will not work.
+ */
+static struct dso *dso__findlink_by_longname(struct rb_root *root,
+                                             struct dso *dso, const char *name)
+{
+        struct rb_node **p = &root->rb_node;
+        struct rb_node  *parent = NULL;
+
+        if (!name)
+                name = dso->long_name;
+        /*
+         * Find node with the matching name
+         */
+        while (*p) {
+                struct dso *this = rb_entry(*p, struct dso, rb_node);
+                int rc = strcmp(name, this->long_name);
+
+                parent = *p;
+                if (rc == 0) {
+                        /*
+                         * In case the new DSO is a duplicate of an existing
+                         * one, print an one-time warning & put the new entry
+                         * at the end of the list of duplicates.
+                         */
+                        if (!dso || (dso == this))
+                                return this;    /* Find matching dso */
+                        /*
+                         * The core kernel DSOs may have duplicated long name.
+                         * In this case, the short name should be different.
+                         * Comparing the short names to differentiate the DSOs.
+                         */
+                        rc = strcmp(dso->short_name, this->short_name);
+                        if (rc == 0) {
+                                pr_err("Duplicated dso name: %s\n", name);
+                                return NULL;
+                        }
+                }
+                if (rc < 0)
+                        p = &parent->rb_left;
+                else
+                        p = &parent->rb_right;
+        }
+        if (dso) {
+                /* Add new node and rebalance tree */
+                rb_link_node(&dso->rb_node, parent, p);
+                rb_insert_color(&dso->rb_node, root);
+        }
+        return NULL;
+}
+
+static inline struct dso *
+dso__find_by_longname(const struct rb_root *root, const char *name)
+{
+        return dso__findlink_by_longname((struct rb_root *)root, NULL, name);
+}
+
 void dso__set_long_name(struct dso *dso, const char *name, bool name_allocated)
 {
         if (name == NULL)
@@ -755,6 +814,7 @@ struct dso *dso__new(const char *name)
                 dso->a2l_fails = 1;
                 dso->kernel = DSO_TYPE_USER;
                 dso->needs_swap = DSO_SWAP__UNSET;
+                RB_CLEAR_NODE(&dso->rb_node);
                 INIT_LIST_HEAD(&dso->node);
                 INIT_LIST_HEAD(&dso->data.open_entry);
         }
@@ -765,6 +825,10 @@ struct dso *dso__new(const char *name)
 void dso__delete(struct dso *dso)
 {
         int i;
+
+        if (!RB_EMPTY_NODE(&dso->rb_node))
+                pr_err("DSO %s is still in rbtree when being deleted!\n",
+                       dso->long_name);
         for (i = 0; i < MAP__NR_TYPES; ++i)
                 symbols__delete(&dso->symbols[i]);
 
@@ -854,6 +918,7 @@ bool __dsos__read_build_ids(struct list_head *head, bool with_hits)
 void dsos__add(struct dsos *dsos, struct dso *dso)
 {
         list_add_tail(&dso->node, &dsos->head);
+        dso__findlink_by_longname(&dsos->root, dso, NULL);
 }
 
 struct dso *dsos__find(const struct dsos *dsos, const char *name,
@@ -867,10 +932,7 @@ struct dso *dsos__find(const struct dsos *dsos, const char *name,
                                 return pos;
                 return NULL;
         }
-        list_for_each_entry(pos, &dsos->head, node)
-                if (strcmp(pos->long_name, name) == 0)
-                        return pos;
-        return NULL;
+        return dso__find_by_longname(&dsos->root, name);
 }
 
 struct dso *__dsos__findnew(struct dsos *dsos, const char *name)
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index b63dc98ad71d..acb651acc7fd 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -91,14 +91,17 @@ struct dso_cache {
 };
 
 /*
- * DSOs are put into a list for fast iteration.
+ * DSOs are put into both a list for fast iteration and rbtree for fast
+ * long name lookup.
  */
 struct dsos {
         struct list_head head;
+        struct rb_root   root;  /* rbtree root sorted by long name */
 };
 
 struct dso {
         struct list_head node;
+        struct rb_node   rb_node;       /* rbtree node sorted by long name */
         struct rb_root   symbols[MAP__NR_TYPES];
         struct rb_root   symbol_names[MAP__NR_TYPES];
         void             *a2l;
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 49a75ec4c47b..b7d477fbda02 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -77,6 +77,7 @@ static void dsos__delete(struct dsos *dsos)
         struct dso *pos, *n;
 
         list_for_each_entry_safe(pos, n, &dsos->head, node) {
+                RB_CLEAR_NODE(&pos->rb_node);
                 list_del(&pos->node);
                 dso__delete(pos);
         }