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 <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: John Stultz <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: maciej-w-rozycki

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 = ' ';