linux-kernel - [PATCH v2] ACPI: NFIT: Optimize nfit_mem

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Message-Id: <20231013122236.2127269-1-visitorckw@gmail.com>
Date:   Fri, 13 Oct 2023 20:22:36 +0800
From:   Kuan-Wei Chiu <visitorckw@...il.com>
To:     dan.j.williams@...el.com, vishal.l.verma@...el.com,
        dave.jiang@...el.com, ira.weiny@...el.com
Cc:     rafael@...nel.org, lenb@...nel.org, nvdimm@...ts.linux.dev,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kuan-Wei Chiu <visitorckw@...il.com>
Subject: [PATCH v2] ACPI: NFIT: Optimize nfit_mem_cmp() for efficiency

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@...il.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;
 }
 
 static int nfit_mem_init(struct acpi_nfit_desc *acpi_desc)
-- 
2.25.1