linux-kernel - [RFC][PATCH 3/2] x86/jump labels: Count and display the short jumps used

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Date:	Wed, 07 Aug 2013 13:54:08 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Jason Baron <jbaron@...mai.com>
Subject: [RFC][PATCH 3/2] x86/jump labels: Count and display the short jumps
 used

On Wed, 2013-08-07 at 13:36 -0400, Steven Rostedt wrote:
> As I said, I would post the patches that let the jmps used by jump labels
> be turn to 2 bytes where possible. These are a bit controversial due
> to the complexity of the update_jump_label code.
> 
> These patches are based off of tip's x86/jumplabel code.
> 
> But if someone cares to play with it, feel free. I'll push this up
> to my repo under: tip/perf/jump-label-7 (internally this is my 7th version).
> 
> I'll post a patch that does the counting as well as a reply to this
> post.

Here's the patch that forces the update and counts the number of short
jumps vs long jumps. It also outputs the locations of the short jumps.

On another box, using a distro config, I had even better results:

[    2.352448] short jumps: 193
[    2.355407]  long jumps: 219

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

Index: linux-trace.git/arch/x86/kernel/jump_label.c
===================================================================
--- linux-trace.git.orig/arch/x86/kernel/jump_label.c
+++ linux-trace.git/arch/x86/kernel/jump_label.c
@@ -44,6 +44,9 @@ static void bug_at(unsigned char *ip, in
 	BUG();
 }
 
+static int short_nops;
+static int long_nops;
+
 static void __jump_label_transform(struct jump_entry *entry,
 				   enum jump_label_type type,
 				   void *(*poker)(void *, const void *, size_t),
@@ -82,9 +85,14 @@ static void __jump_label_transform(struc
 		 */
 		if (init) {
 			/* Ignore short nops, we do not change them */
-			if (memcmp(ip, nop_short, 2) == 0)
+			if (memcmp(ip, nop_short, 2) == 0) {
+				short_nops++;
+				printk("short jump at: %pS %p\n",
+				       (void *)ip, (void *)ip);
 				return;
+			}
 
+			long_nops++;
 			/* We are initializing from the default nop */
 			if (unlikely(memcmp(ip, default_nop, 5) != 0))
 				bug_at(ip, __LINE__);
@@ -154,7 +162,7 @@ __init_or_module void arch_jump_label_tr
 	if (jlstate == JL_STATE_START) {
 		const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
 
-		if (memcmp(ideal_nop, default_nop, 5) != 0)
+		if (1 || memcmp(ideal_nop, default_nop, 5) != 0)
 			jlstate = JL_STATE_UPDATE;
 		else
 			jlstate = JL_STATE_NO_UPDATE;
@@ -162,4 +170,11 @@ __init_or_module void arch_jump_label_tr
 	if (jlstate == JL_STATE_UPDATE)
 		__jump_label_transform(entry, type, text_poke_early, 1);
 }
+
+static __init int output_jumps(void)
+{
+	printk("short jumps: %d\n", short_nops);
+	printk(" long jumps: %d\n", long_nops);
+}
+late_initcall(output_jumps);
 #endif


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