linux-kernel - [PATCH 2/2] riscv: Optimize memset

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Date:   Wed, 10 May 2023 11:52:42 +0800
From:   zhangfei <zhang_fei_0403@....com>
To:     ajones@...tanamicro.com
Cc:     aou@...s.berkeley.edu, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, palmer@...belt.com,
        paul.walmsley@...ive.com, zhang_fei_0403@....com,
        zhangfei@...iscas.ac.cn
Subject: [PATCH 2/2] riscv: Optimize memset

From: zhangfei <zhangfei@...iscas.ac.cn>

This patch has been optimized for memset data sizes less than 16 bytes.
Compared to byte by byte storage, significant performance improvement has been achieved.
It allows storage instructions to be executed in parallel and reduces the number of jumps.

Signed-off-by: Fei Zhang <zhangfei@...iscas.ac.cn>
---
 arch/riscv/lib/memset.S | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/lib/memset.S b/arch/riscv/lib/memset.S
index e613c5c27998..6113a2696e79 100644
--- a/arch/riscv/lib/memset.S
+++ b/arch/riscv/lib/memset.S
@@ -106,9 +106,36 @@ WEAK(memset)
 	beqz	a2, 6f
 	add	a3, t0, a2
 5:
-	sb	a1, 0(t0)
-	addi	t0, t0, 1
-	bltu	t0, a3, 5b
+       sb      a1,  0(t0)
+       sb      a1, -1(a3)
+       li      a4, 2
+       bgeu    a4, a2, 6f
+
+       sb 	a1,  1(t0)
+       sb 	a1,  2(t0)
+       sb 	a1, -2(a3)
+       sb 	a1, -3(a3)
+       li 	a4, 6
+       bgeu 	a4, a2, 6f
+
+       sb 	a1,  3(t0)
+       sb 	a1, -4(a3)
+       li 	a4, 8
+       bgeu    a4, a2, 6f
+
+       sb 	a1,  4(t0)
+       sb 	a1, -5(a3)
+       li 	a4, 10
+       bgeu 	a4, a2, 6f
+
+       sb 	a1,  5(t0)
+       sb 	a1,  6(t0)
+       sb 	a1, -6(a3)
+       sb 	a1, -7(a3)
+       li 	a4, 14
+       bgeu 	a4, a2, 6f
+
+       sb 	a1, 7(t0)
 6:
 	ret
 END(__memset)
-- 
2.33.0