linux-kernel - [PATCH 08/16] ftrace: Use bsearch to find record ip

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Date:	Wed, 21 Dec 2011 07:36:32 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: [PATCH 08/16] ftrace: Use bsearch to find record ip

From: Steven Rostedt <srostedt@...hat.com>

Now that each set of pages in the function list are sorted by
ip, we can use bsearch to find a record within each set of pages.
This speeds up the ftrace_location() function by magnitudes.

For archs (like x86) that need to add a breakpoint at every function
that will be converted from a nop to a callback and vice versa,
the breakpoint callback needs to know if the breakpoint was for
ftrace or not. It requires finding the breakpoint ip within the
records. Doing a linear search is extremely inefficient. It is
a must to be able to do a fast binary search to find these locations.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/trace/ftrace.c |   38 +++++++++++++++++++++++---------------
 1 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 2d6f8bc..dcd3a81 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -22,6 +22,7 @@
 #include <linux/hardirq.h>
 #include <linux/kthread.h>
 #include <linux/uaccess.h>
+#include <linux/bsearch.h>
 #include <linux/module.h>
 #include <linux/ftrace.h>
 #include <linux/sysctl.h>
@@ -1300,6 +1301,19 @@ ftrace_ops_test(struct ftrace_ops *ops, unsigned long ip)
 		}				\
 	}
 
+
+static int ftrace_cmp_recs(const void *a, const void *b)
+{
+	const struct dyn_ftrace *reca = a;
+	const struct dyn_ftrace *recb = b;
+
+	if (reca->ip > recb->ip)
+		return 1;
+	if (reca->ip < recb->ip)
+		return -1;
+	return 0;
+}
+
 /**
  * ftrace_location - return true if the ip giving is a traced location
  * @ip: the instruction pointer to check
@@ -1313,11 +1327,17 @@ int ftrace_location(unsigned long ip)
 {
 	struct ftrace_page *pg;
 	struct dyn_ftrace *rec;
+	struct dyn_ftrace key;
 
-	do_for_each_ftrace_rec(pg, rec) {
-		if (rec->ip == ip)
+	key.ip = ip;
+
+	for (pg = ftrace_pages_start; pg; pg = pg->next) {
+		rec = bsearch(&key, pg->records, pg->index,
+			      sizeof(struct dyn_ftrace),
+			      ftrace_cmp_recs);
+		if (rec)
 			return 1;
-	} while_for_each_ftrace_rec();
+	}
 
 	return 0;
 }
@@ -3587,18 +3607,6 @@ static void ftrace_swap_recs(void *a, void *b, int size)
 	*recb = t;
 }
 
-static int ftrace_cmp_recs(const void *a, const void *b)
-{
-	const struct dyn_ftrace *reca = a;
-	const struct dyn_ftrace *recb = b;
-
-	if (reca->ip > recb->ip)
-		return 1;
-	if (reca->ip < recb->ip)
-		return -1;
-	return 0;
-}
-
 static int ftrace_process_locs(struct module *mod,
 			       unsigned long *start,
 			       unsigned long *end)
-- 
1.7.7.3



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