diff mbox series

time: Use div64_long() instead of do_div()

Message ID 20240225232541.17659-2-thorsten.blum@toblux.com
State New
Headers
Series time: Use div64_long() instead of do_div() |

Commit Message

Thorsten Blum Feb. 25, 2024, 11:25 p.m. UTC 
  Fixes Coccinelle/coccicheck warning reported by do_div.cocci.

Compared to do_div(), div64_long() does not implicitly cast the divisor and
does not unnecessarily calculate the remainder.

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
---
 kernel/time/jiffies.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Liao Chang Feb. 26, 2024, 3:28 a.m. UTC | #1 
Thorsten,

在 2024/2/26 7:25, Thorsten Blum 写道:
> Fixes Coccinelle/coccicheck warning reported by do_div.cocci.
> 
> Compared to do_div(), div64_long() does not implicitly cast the divisor and
> does not unnecessarily calculate the remainder.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
> ---
>  kernel/time/jiffies.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
> index bc4db9e5ab70..9d23178e2b6a 100644
> --- a/kernel/time/jiffies.c
> +++ b/kernel/time/jiffies.c
> @@ -91,7 +91,7 @@ int register_refined_jiffies(long cycles_per_second)
>  	/* shift_hz stores hz<<8 for extra accuracy */
>  	shift_hz = (u64)cycles_per_second << 8;
>  	shift_hz += cycles_per_tick/2;
> -	do_div(shift_hz, cycles_per_tick);
> +	shift_hz = div64_long(shift_hz, cycles_per_tick);

I am considering using div64_ul() to calculate the result. as shift_hz is
unsigned long, assume the sign bit of divisor cycles_per_tick never be set
in this context,then div64_long() will do a extra sign extension for result.
Or are there other recommendations?

Thanks.

>  	/* Calculate nsec_per_tick using shift_hz */
>  	nsec_per_tick = (u64)NSEC_PER_SEC << 8;
>  	nsec_per_tick += (u32)shift_hz/2;
Thorsten Blum Feb. 26, 2024, 8:27 a.m. UTC | #2 
> On Feb 26, 2024, at 04:28, Liao, Chang <liaochang1@huawei.com> wrote:
> 
> I am considering using div64_ul() to calculate the result. as shift_hz is
> unsigned long, assume the sign bit of divisor cycles_per_tick never be set
> in this context,then div64_long() will do a extra sign extension for result.

Yes, div64_ul() is better and also removes the warning.

I'll submit a v2 shortly.

Thanks,
Thorsten
diff mbox series

Patch

diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index bc4db9e5ab70..9d23178e2b6a 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -91,7 +91,7 @@  int register_refined_jiffies(long cycles_per_second)
 	/* shift_hz stores hz<<8 for extra accuracy */
 	shift_hz = (u64)cycles_per_second << 8;
 	shift_hz += cycles_per_tick/2;
-	do_div(shift_hz, cycles_per_tick);
+	shift_hz = div64_long(shift_hz, cycles_per_tick);
 	/* Calculate nsec_per_tick using shift_hz */
 	nsec_per_tick = (u64)NSEC_PER_SEC << 8;
 	nsec_per_tick += (u32)shift_hz/2;