linux-kernel - Re: [PATCH v1] tools: timers: fix freq average calculation

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Date:   Wed, 5 Jul 2023 20:46:03 -0700
From:   John Stultz <jstultz@...gle.com>
To:     Minjie Du <duminjie@...o.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>, Shuah Khan <shuah@...nel.org>,
        "open list:TIMEKEEPING, CLOCKSOURCE CORE, NTP, ALARMTIMER" 
        <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, opensource.kernel@...o.com
Subject: Re: [PATCH v1] tools: timers: fix freq average calculation

On Wed, Jul 5, 2023 at 8:23 PM Minjie Du <duminjie@...o.com> wrote:
>
> Delete a duplicate assignment from this function implementation.
> The note means ppm is average of the two actual freq samples.
> But ppm have a duplicate assignment.
>
> Signed-off-by: Minjie Du <duminjie@...o.com>
> ---
>  tools/testing/selftests/timers/raw_skew.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/timers/raw_skew.c b/tools/testing/selftests/timers/raw_skew.c
> index 5beceeed0..6eba203f9 100644
> --- a/tools/testing/selftests/timers/raw_skew.c
> +++ b/tools/testing/selftests/timers/raw_skew.c
> @@ -129,8 +129,7 @@ int main(int argc, char **argv)
>         printf("%lld.%i(est)", eppm/1000, abs((int)(eppm%1000)));
>
>         /* Avg the two actual freq samples adjtimex gave us */
> -       ppm = (tx1.freq + tx2.freq) * 1000 / 2;
> -       ppm = (long long)tx1.freq * 1000;
> +       ppm = (long long)(tx1.freq + tx2.freq) * 1000 / 2;

Huh. So yeah, I looked back in my own history and this has been there
forever. I'm guessing I was intending to average the two samples and
then due to reasons I can't remember decided to just use the first in
the short-term for some debugging (with the second assignment) and
committed both.

I think it should be safe, because if the freq values are not the same
the test will return SKIP, so it's unlikely changing this would cause
new test failures.

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

Thanks for noticing this and sending this out!
-john