2008-08-25 21:49:45

by Joe Korty

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)

2008-08-26 08:37:46

by Ingo Molnar

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

* Joe Korty <[email protected]> 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