linux-kernel - RE: [PATCH] perf/x86/amd/power: Use div64_u64 onstead of do

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Date: Thu, 2 May 2024 16:25:58 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Jules Irenge' <jbi.octave@...il.com>, "mark.rutland@....com"
	<mark.rutland@....com>
CC: "alexander.shishkin@...ux.intel.com" <alexander.shishkin@...ux.intel.com>,
	"jolsa@...nel.org" <jolsa@...nel.org>, "irogers@...gle.com"
	<irogers@...gle.com>, "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
	"bp@...en8.de" <bp@...en8.de>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "x86@...nel.org" <x86@...nel.org>,
	"hpa@...or.com" <hpa@...or.com>, "linux-perf-users@...r.kernel.org"
	<linux-perf-users@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] perf/x86/amd/power: Use div64_u64 onstead of do_div()

From: Jules Irenge <jbi.octave@...il.com>
> Sent: 28 April 2024 17:40
> 
> do_div() truncates a u64 divisor to 32 bit.
> This can lead to non-zero being truncated to zero for division.
> 
> Fix coccinelle warning
> WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead
> 
> Signed-off-by: Jules Irenge <jbi.octave@...il.com>
> ---
>  arch/x86/events/amd/power.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> 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)
>  	delta *= cpu_pwr_sample_ratio * 1000;
>  	tdelta = new_ptsc - prev_ptsc;
> 
> -	do_div(delta, tdelta);
> +	div64_u64(delta, tdelta);

Nak - you've not tested it.

	David

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

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