linux-kernel - Re: [PATCH 1/3] sched_clock: Round the frequency reported to nearest rather than down

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Message-ID: <CANDhNCrQQ5cUYzSr8pTdfbpvRrwJxWtTZxqvkGGdZiPXkfvr1Q@mail.gmail.com>
Date:   Tue, 26 Apr 2022 13:38:40 -0700
From:   John Stultz <jstultz@...gle.com>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] sched_clock: Round the frequency reported to nearest
 rather than down

On Sun, Apr 24, 2022 at 4:47 AM Maciej W. Rozycki <macro@...am.me.uk> wrote:
>
> 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@...am.me.uk>
> Fixes: 112f38a4a316 ("ARM: sched_clock: provide common infrastructure for sched_clock()")
> ---

This seems sane to me.

Acked-by: John Stultz <jstultz@...gle.com>

thanks
-john