Re: [PATCH] mtd: spi-nor: replace unnecessary div64_u64() with div_u64()

Pratyush Yadav
2024-04-29T14:42:33Z

> Hi,
>
> On Mon Apr 29, 2024 at 3:27 PM CEST, Pratyush Yadav wrote:
>> On Mon, Apr 29 2024, Michael Walle wrote:
>>
>> > Both occurences of div64_u64() just have a u8 or u32 divisor. Use
>> > div_u64() instead.
>>
>> Does this improve performance or is this only for correctness?
>
> See function doc for div_u64():
>
> * This is the most common 64bit divide and should be used if possible,
> * as many 32bit archs can optimize this variant better than a full 64bit
> * divide.

Thanks. I think it would be good to add this to the commit message:

Both occurences of div64_u64() just have a u8 or u32 divisor. Use
div_u64() instead. Many 32 bit architectures can optimize this
variant better than a full 64 bit divide.

No need to resend, I can do this when applying.

>
>> Patch LGTM otherwise.
>>
>> Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
>>
>> BTW, I also noticed that there is a do_div() call in spi_nor_write()
>> that also uses a u64 dividend and u32 divisor. I was wondering why it
>> uses do_div() and not div_u64() (I am not sure what the difference
>> between the two is) but I suppose it doesn't matter much since your
>> spring cleaning series will delete that code anyway.
>
> do_div() is a macro and is modifying the dividend in place, whereas
> div_u64() will return it. do_div() is using u32 for the divisor
> anyway.
>
> -michael
>