Commit 92067440 authored by Maciej W. Rozycki's avatar Maciej W. Rozycki Committed by Thomas Gleixner
Browse files

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: default avatarMaciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarJohn Stultz <jstultz@google.com>
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2204240055590.9383@angie.orcam.me.uk
parent 90be8d6c

kernel/time/sched_clock.c

+3 −2
Original line number Diff line number Diff line
@@ -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 = ' ';