From: "Maciej W. Rozycki" <macro@orcam.me.uk>
To: John Stultz <jstultz@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Stephen Boyd <sboyd@kernel.org>,
Russell King <linux@armlinux.org.uk>,
Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH 1/3] sched_clock: Round the frequency reported to nearest rather than down
Date: Sun, 24 Apr 2022 12:47:20 +0100 (BST) [thread overview]
Message-ID: <alpine.DEB.2.21.2204240055590.9383@angie.orcam.me.uk> (raw)
In-Reply-To: <alpine.DEB.2.21.2204211556270.9383@angie.orcam.me.uk>
We currently round the frequency reported for clock sources down, which
gives misleading figures, e.g.:
I/O ASIC clock frequency 24999480Hz
clocksource: dec-ioasic: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 76452008078 ns
sched_clock: 32 bits at 24MHz, resolution 40ns, wraps every 85901132779ns
MIPS counter frequency 59998512Hz
clocksource: MIPS: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 31855130776 ns
sched_clock: 32 bits at 59MHz, resolution 16ns, wraps every 35792281591ns
Rounding to nearest seems more adequate:
I/O ASIC clock frequency 24999664Hz
clocksource: dec-ioasic: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 76451445358 ns
sched_clock: 32 bits at 25MHz, resolution 40ns, wraps every 85900499947ns
MIPS counter frequency 59999728Hz
clocksource: MIPS: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 31854485176 ns
sched_clock: 32 bits at 60MHz, resolution 16ns, wraps every 35791556599ns
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Fixes: 112f38a4a316 ("ARM: sched_clock: provide common infrastructure for sched_clock()")
---
kernel/time/sched_clock.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
linux-sched-clock-rate-round.diff
Index: linux-macro/kernel/time/sched_clock.c
===================================================================
--- linux-macro.orig/kernel/time/sched_clock.c
+++ linux-macro/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),
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 = ' ';
next prev parent reply other threads:[~2022-04-24 11:47 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-24 11:47 [PATCH 0/3] sched_clock: Fixes for frequency reporting Maciej W. Rozycki
2022-04-24 11:47 ` Maciej W. Rozycki [this message]
2022-04-26 20:38 ` [PATCH 1/3] sched_clock: Round the frequency reported to nearest rather than down John Stultz
2022-05-02 12:31 ` [tip: timers/core] time/sched_clock: " tip-bot2 for Maciej W. Rozycki
2022-04-24 11:47 ` [PATCH 2/3] sched_clock: Use Hz as the unit for clock rate reporting below 4kHz Maciej W. Rozycki
2022-05-02 12:31 ` [tip: timers/core] time/sched_clock: " tip-bot2 for Maciej W. Rozycki
2022-04-24 11:47 ` [PATCH 3/3] sched_clock: Fix formatting of frequency reporting code Maciej W. Rozycki
2022-04-26 20:41 ` John Stultz
2022-05-02 12:31 ` [tip: timers/core] time/sched_clock: " tip-bot2 for Maciej W. Rozycki
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