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Subject[PATCH v2 2/2] RISC-V: lib: Optimize memset performance
Date
From: zhangfei <zhangfei@nj.iscas.ac.cn>

Optimized performance when the data size is 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.
Additional checks can avoid redundant stores.

Signed-off-by: Fei Zhang <zhangfei@nj.iscas.ac.cn>
---
arch/riscv/lib/memset.S | 40 +++++++++++++++++++++++++++++++++++++---
1 file changed, 37 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/lib/memset.S b/arch/riscv/lib/memset.S
index e613c5c27998..452764bc9900 100644
--- a/arch/riscv/lib/memset.S
+++ b/arch/riscv/lib/memset.S
@@ -106,9 +106,43 @@ WEAK(memset)
beqz a2, 6f
add a3, t0, a2
5:
- sb a1, 0(t0)
- addi t0, t0, 1
- bltu t0, a3, 5b
+ /* fill head and tail with minimal branching */
+ 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
+
+ /*
+ * Adding additional detection to avoid
+ * redundant stores can lead
+ * to better performance
+ */
+ 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
+
+ /* store the last byte */
+ sb a1, 7(t0)
6:
ret
END(__memset)
--
2.33.0
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