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SubjectRe: [PATCH v2] ACPI: NFIT: Optimize nfit_mem_cmp() for efficiency
On Fri, Oct 13, 2023 at 2:22 PM Kuan-Wei Chiu <visitorckw@gmail.com> wrote:
>
> The original code used conditional branching in the nfit_mem_cmp
> function to compare two values and return -1, 1, or 0 based on the
> result. However, the list_sort comparison function only needs results
> <0, >0, or =0. This patch optimizes the code to make the comparison
> branchless, improving efficiency and reducing code size. This change
> reduces the number of comparison operations from 1-2 to a single
> subtraction operation, thereby saving the number of instructions.
>
> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> ---
> v1 -> v2:
> - Add explicit type cast in case the sizes of u32 and int differ.
>
> drivers/acpi/nfit/core.c | 6 +-----
> 1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
> index f96bf32cd368..563a32eba888 100644
> --- a/drivers/acpi/nfit/core.c
> +++ b/drivers/acpi/nfit/core.c
> @@ -1138,11 +1138,7 @@ static int nfit_mem_cmp(void *priv, const struct list_head *_a,
>
> handleA = __to_nfit_memdev(a)->device_handle;
> handleB = __to_nfit_memdev(b)->device_handle;
> - if (handleA < handleB)
> - return -1;
> - else if (handleA > handleB)
> - return 1;
> - return 0;
> + return (int)handleA - (int)handleB;

Are you sure that you are not losing bits in these conversions?

> }
>
> static int nfit_mem_init(struct acpi_nfit_desc *acpi_desc)
> --

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