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Subject[tip: timers/core] time/sched_clock: Round the frequency reported to nearest rather than down
The following commit has been merged into the timers/core branch of tip:

Commit-ID: 92067440f1311dfa4d77b57a9da6b3706f5da32e
Gitweb: https://git.kernel.org/tip/92067440f1311dfa4d77b57a9da6b3706f5da32e
Author: Maciej W. Rozycki <macro@orcam.me.uk>
AuthorDate: Sun, 24 Apr 2022 12:47:20 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 02 May 2022 14:29:04 +02:00

time/sched_clock: Round the frequency reported to nearest rather than down

The frequency reported for clock sources are rounded down, which gives
misleading figures, e.g.:

I/O ASIC clock frequency 24999480Hz
sched_clock: 32 bits at 24MHz, resolution 40ns, wraps every 85901132779ns
MIPS counter frequency 59998512Hz
sched_clock: 32 bits at 59MHz, resolution 16ns, wraps every 35792281591ns

Rounding to nearest is more adequate:

I/O ASIC clock frequency 24999664Hz
sched_clock: 32 bits at 25MHz, resolution 40ns, wraps every 85900499947ns
MIPS counter frequency 59999728Hz
sched_clock: 32 bits at 60MHz, resolution 16ns, wraps every 35791556599ns

Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2204240055590.9383@angie.orcam.me.uk

---
kernel/time/sched_clock.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index b1b9b12..ee07f3a 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -8,6 +8,7 @@
#include <linux/jiffies.h>
#include <linux/ktime.h>
#include <linux/kernel.h>
+#include <linux/math.h>
#include <linux/moduleparam.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
@@ -199,11 +200,11 @@ sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)

r = rate;
if (r >= 4000000) {
- r /= 1000000;
+ r = DIV_ROUND_CLOSEST(r, 1000000);
r_unit = 'M';
} else {
if (r >= 1000) {
- r /= 1000;
+ r = DIV_ROUND_CLOSEST(r, 1000);
r_unit = 'k';
} else {
r_unit = ' ';
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