[PATCH] lockstat - fix numerical output rounding error

[PATCH] lockstat - fix numerical output rounding error

[Joe Korty]

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)

Re: [PATCH] lockstat - fix numerical output rounding error

[Ingo Molnar]

* Joe Korty <joe.korty@ccur.com> wrote:

> 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

applied to tip/core/urgent - thanks Joe!

(btw., please include Signed-off-by lines in your patches in the future)

	Ingo