linux-kernel - [PATCH] lockstat - fix numerical output rounding error

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Message-ID: <20080825211533.GA27943@tsunami.ccur.com>
Date:	Mon, 25 Aug 2008 17:15:33 -0400
From:	Joe Korty <joe.korty@...r.com>
To:	mingo@...e.hu
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] lockstat - fix numerical output rounding error

Fix rounding error in /proc/lock_stat numerical output.

On occasion the two digit fractional part contains the three
digit value '100'.  This is due to a bug in the rounding algorithm
which pushes values in the range '95..99' to '100' rather than
to '00' + an increment to the integer part.  For example,

	- 123456.100      old display
	+ 123457.00	  new display

Index: 2.6.26/kernel/lockdep_proc.c
===================================================================
--- 2.6.26.orig/kernel/lockdep_proc.c	2008-07-13 17:51:29.000000000 -0400
+++ 2.6.26/kernel/lockdep_proc.c	2008-08-25 16:58:04.000000000 -0400
@@ -406,8 +406,9 @@
 {
 	unsigned long rem;
 
+	nr += 5; /* for display rounding */
 	rem = do_div(nr, 1000); /* XXX: do_div_signed */
-	snprintf(buf, bufsiz, "%lld.%02d", (long long)nr, ((int)rem+5)/10);
+	snprintf(buf, bufsiz, "%lld.%02d", (long long)nr, (int)rem/10);
 }
 
 static void seq_time(struct seq_file *m, s64 time)
--
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