linux-kernel - [PATCH] riscv: uaccess: Relax the threshold for fast path

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Message-Id: <20240313091929.4029960-1-xiao.w.wang@intel.com>
Date: Wed, 13 Mar 2024 17:19:29 +0800
From: Xiao Wang <xiao.w.wang@...el.com>
To: paul.walmsley@...ive.com,
	palmer@...belt.com,
	aou@...s.berkeley.edu
Cc: jerry.shih@...ive.com,
	nick.knight@...ive.com,
	ajones@...tanamicro.com,
	bjorn@...osinc.com,
	andy.chiu@...ive.com,
	viro@...iv.linux.org.uk,
	cleger@...osinc.com,
	alexghiti@...osinc.com,
	haicheng.li@...el.com,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Xiao Wang <xiao.w.wang@...el.com>
Subject: [PATCH] riscv: uaccess: Relax the threshold for fast path

The bytes copy for unaligned head would cover at most SZREG-1 bytes, so
it's better to set the threshold as >= (SZREG-1 + word_copy stride size)
which equals to 9*SZREG-1.

Signed-off-by: Xiao Wang <xiao.w.wang@...el.com>
---
 arch/riscv/lib/uaccess.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S
index bc22c078aba8..2e665f8f8fcc 100644
--- a/arch/riscv/lib/uaccess.S
+++ b/arch/riscv/lib/uaccess.S
@@ -44,7 +44,7 @@ SYM_FUNC_START(fallback_scalar_usercopy)
 	 * Use byte copy only if too small.
 	 * SZREG holds 4 for RV32 and 8 for RV64
 	 */
-	li	a3, 9*SZREG /* size must be larger than size in word_copy */
+	li	a3, 9*SZREG-1 /* size must >= (word_copy stride + SZREG-1) */
 	bltu	a2, a3, .Lbyte_copy_tail
 
 	/*
-- 
2.25.1