From 301011ba622513cb41ced59973972204e0da2f71 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Date: Wed, 28 Aug 2019 15:05:29 -0400
Subject: [PATCH] tools lib traceevent: Remove unneeded qsort and uses memmove
 instead
Git-commit: 301011ba622513cb41ced59973972204e0da2f71
References: git-fixes
Patch-mainline: v5.4-rc1


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>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 tools/lib/traceevent/event-parse.c |   55 ++++++++++++++++++++++++++++++++-----
 1 file changed, 49 insertions(+), 6 deletions(-)

--- a/tools/lib/traceevent/event-parse.c
+++ b/tools/lib/traceevent/event-parse.c
@@ -154,6 +154,25 @@ static int cmdline_cmp(const void *a, co
 	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;
@@ -249,6 +268,7 @@ static int add_new_comm(struct pevent *p
 	struct cmdline *cmdlines = pevent->cmdlines;
 	const struct cmdline *cmdline;
 	struct cmdline key;
+	int cnt;
 
 	if (!pid)
 		return 0;
@@ -270,18 +290,41 @@ static int add_new_comm(struct pevent *p
 	}
 	pevent->cmdlines = cmdlines;
 
-	cmdlines[pevent->cmdline_count].comm = strdup(comm);
-	if (!cmdlines[pevent->cmdline_count].comm) {
+	key.comm = strdup(comm);
+	if (!key.comm) {
 		errno = ENOMEM;
 		return -1;
 	}
 
-	cmdlines[pevent->cmdline_count].pid = pid;
-		
-	if (cmdlines[pevent->cmdline_count].comm)
+	if (!tep->cmdline_count) {
+		/* no entries yet */
+		tep->cmdlines[0] = key;
 		pevent->cmdline_count++;
+		return 0;
+	}
 
-	qsort(cmdlines, pevent->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;
 }