linux-kernel - [PATCH] printk: Optimize if statement logic where newline exists

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Message-ID: <1340984411.16702.127.camel@gandalf.stny.rr.com>
Date:	Fri, 29 Jun 2012 11:40:11 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Kay Sievers <kay@...y.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Joe Perches <joe@...ches.com>,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: [PATCH] printk: Optimize if statement logic where newline exists

In reviewing Kay's fix up patch: "printk: Have printk() never buffer its
data", I found two if statements that could be combined and optimized.

Put together the two 'cont.len && cont.owner == current' if statements
into a single one, and check if we need to call cont_add(). This also
removes the unneeded double cont_flush() calls.

Link: http://lkml.kernel.org/r/1340869133.876.10.camel@mop

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

[ This patch is dependent on Kay's patch, referenced at the above Link ]

Index: linux-trace.git/kernel/printk.c
===================================================================
--- linux-trace.git.orig/kernel/printk.c
+++ linux-trace.git/kernel/printk.c
@@ -1474,15 +1474,14 @@ asmlinkage int vprintk_emit(int facility
 		bool stored = false;
 
 		/*
-		 * Flush the conflicting buffer. An earlier newline was missing,
-		 * or we race with a continuation line from an interrupt.
+		 * If an earlier newline was missing and it was the same task,
+		 * either merge it with the current buffer and flush, or if
+		 * there was a race with interrupts (prefix == true) then just
+		 * flush it out and store this line separately.
 		 */
-		if (cont.len && prefix && cont.owner == current)
-			cont_flush();
-
-		/* Merge with our buffer if possible; flush it in any case */
 		if (cont.len && cont.owner == current) {
-			stored = cont_add(facility, level, text, text_len);
+			if (!prefix)
+				stored = cont_add(facility, level, text, text_len);
 			cont_flush();
 		}
 


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