[PATCH 37/37] tools lib traceevent: Remove unneeded qsort and uses memmove instead

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

While reading a trace data file that had 100,000s of tasks, the process
took an extremely long time. I profiled it down to add_new_comm(), which
was doing a qsort() call on an array that was pretty much already sorted
(all but the last element. qsort() isn't very efficient when dealing
with mostly sorted arrays, and this definitely showed its issues.

When adding a new task to the task list, instead of using qsort(), do
another bsearch() with a function that will find the element before
where the new task will be inserted in. Then simply shift the rest of
the array, and insert the task where it belongs.

Fixes: f7d82350e597d ("tools/events: Add files to create libtraceevent.a")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linux-trace-devel@vger.kernel.org
Link: http://lkml.kernel.org/r/20190828191820.127233764@goodmis.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/lib/traceevent/event-parse.c | 55 ++++++++++++++++++++++++++----
 1 file changed, 49 insertions(+), 6 deletions(-)

diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
index 13fd9fdf91e0..3e83636076b2 100644
--- a/tools/lib/traceevent/event-parse.c
+++ b/tools/lib/traceevent/event-parse.c
@@ -142,6 +142,25 @@ static int cmdline_cmp(const void *a, const void *b)
 	return 0;
 }
 
+/* Looking for where to place the key */
+static int cmdline_slot_cmp(const void *a, const void *b)
+{
+	const struct tep_cmdline *ca = a;
+	const struct tep_cmdline *cb = b;
+	const struct tep_cmdline *cb1 = cb + 1;
+
+	if (ca->pid < cb->pid)
+		return -1;
+
+	if (ca->pid > cb->pid) {
+		if (ca->pid <= cb1->pid)
+			return 0;
+		return 1;
+	}
+
+	return 0;
+}
+
 struct cmdline_list {
 	struct cmdline_list	*next;
 	char			*comm;
@@ -239,6 +258,7 @@ static int add_new_comm(struct tep_handle *tep,
 	struct tep_cmdline *cmdline;
 	struct tep_cmdline key;
 	char *new_comm;
+	int cnt;
 
 	if (!pid)
 		return 0;
@@ -271,18 +291,41 @@ static int add_new_comm(struct tep_handle *tep,
 	}
 	tep->cmdlines = cmdlines;
 
-	cmdlines[tep->cmdline_count].comm = strdup(comm);
-	if (!cmdlines[tep->cmdline_count].comm) {
+	key.comm = strdup(comm);
+	if (!key.comm) {
 		errno = ENOMEM;
 		return -1;
 	}
 
-	cmdlines[tep->cmdline_count].pid = pid;
-		
-	if (cmdlines[tep->cmdline_count].comm)
+	if (!tep->cmdline_count) {
+		/* no entries yet */
+		tep->cmdlines[0] = key;
 		tep->cmdline_count++;
+		return 0;
+	}
 
-	qsort(cmdlines, tep->cmdline_count, sizeof(*cmdlines), cmdline_cmp);
+	/* Now find where we want to store the new cmdline */
+	cmdline = bsearch(&key, tep->cmdlines, tep->cmdline_count - 1,
+			  sizeof(*tep->cmdlines), cmdline_slot_cmp);
+
+	cnt = tep->cmdline_count;
+	if (cmdline) {
+		/* cmdline points to the one before the spot we want */
+		cmdline++;
+		cnt -= cmdline - tep->cmdlines;
+
+	} else {
+		/* The new entry is either before or after the list */
+		if (key.pid > tep->cmdlines[tep->cmdline_count - 1].pid) {
+			tep->cmdlines[tep->cmdline_count++] = key;
+			return 0;
+		}
+		cmdline = &tep->cmdlines[0];
+	}
+	memmove(cmdline + 1, cmdline, (cnt * sizeof(*cmdline)));
+	*cmdline = key;
+
+	tep->cmdline_count++;
 
 	return 0;
 }
-- 
2.21.0