2024-04-28 16:40:41

by Jules Irenge

Subject: [PATCH] perf/x86/amd/power: Use div64_u64 onstead of do_div()

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 <[email protected]>
---
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);
local64_add(delta, &event->count);
}

--
2.43.2

2024-05-02 16:26:49

by David Laight

Subject: RE: [PATCH] perf/x86/amd/power: Use div64_u64 onstead of do_div()

From: Jules Irenge <[email protected]>
> 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 <[email protected]>
> ---
> 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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