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From: David Laight <David.Laight@ACULAB.COM>
To: 'Jules Irenge' <jbi.octave@gmail.com>, "mark.rutland@arm.com"
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Subject: RE: [PATCH] perf/x86/amd/power: Use div64_u64 onstead of do_div()
Thread-Topic: [PATCH] perf/x86/amd/power: Use div64_u64 onstead of do_div()
Thread-Index: AQHamYq9w5OrjuroEEyWIm0jPSXs6bGEJ7/A
Date: Thu, 2 May 2024 16:25:58 +0000
Message-ID: <41180245c6e94a06b789cd44b8aebd62@AcuMS.aculab.com>
References: <Zi57-TMgU19puaQM@octinomon.home>
In-Reply-To: <Zi57-TMgU19puaQM@octinomon.home>
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From: Jules Irenge <jbi.octave@gmail.com>
> Sent: 28 April 2024 17:40
>=20
> do_div() truncates a u64 divisor to 32 bit.
> This can lead to non-zero being truncated to zero for division.
>=20
> Fix coccinelle warning
> WARNING: do_div() does a 64-by-32 division, please consider using div64_u=
64 instead
>=20
> Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
> ---
>  arch/x86/events/amd/power.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> diff --git a/arch/x86/events/amd/power.c b/arch/x86/events/amd/power.c
> index 37d5b380516e..ff003c1a645b 100644
> --- a/arch/x86/events/amd/power.c
> +++ b/arch/x86/events/amd/power.c
> @@ -64,7 +64,7 @@ static void event_update(struct perf_event *event)
>  =09delta *=3D cpu_pwr_sample_ratio * 1000;
>  =09tdelta =3D new_ptsc - prev_ptsc;
>=20
> -=09do_div(delta, tdelta);
> +=09div64_u64(delta, tdelta);

Nak - you've not tested it.

=09David

>  =09local64_add(delta, &event->count);
>  }
>=20
> --
> 2.43.2
>=20

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