Messages in this thread Patch in this message |  | | Date | Sun, 24 Apr 2022 12:47:20 +0100 (BST) | From | "Maciej W. Rozycki" <> | Subject | [PATCH 1/3] sched_clock: Round the frequency reported to nearest rather than down |
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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 = ' ';
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