From b94cec5761d22624d109d859467d7d4ce0a1b88b Mon Sep 17 00:00:00 2001 From: Andy Chiu Date: Tue, 1 Sep 2026 14:23:32 -0500 Subject: [PATCH] riscv: skip software algning code for HAVE_EFFICIENT_UNALIGNED_ACCESS We can jump straight into the copy loop if the kernel is compiled for a hardware that natively supports misaligned access. The user copy bandwidth improvement on K3 and Ascaolon is shown as below: Misaligned user copy, size: 512B (offset: [0:15] except 0, 8) BW Improvement | Write | Read | K3 | 6.19% | 3.43% | Ascalon | 10.0% | 11.4% | Aligned user copy, size: 512B (offset: 0, 8) BW Improvement | Write | Read | K3 | 1.69% | 0.90% | Ascalon | 1.25% | 3.32% | Suggested-by: Anton Blanchard Signed-off-by: Andy Chiu Link: https://patch.msgid.link/20260901192334.3543340-1-tchiu@tenstorrent.com Signed-off-by: Paul Walmsley --- arch/riscv/lib/uaccess.S | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S index 4efea1b3326c..cf8586a937de 100644 --- a/arch/riscv/lib/uaccess.S +++ b/arch/riscv/lib/uaccess.S @@ -76,6 +76,7 @@ SYM_FUNC_START(fallback_scalar_usercopy_sum_enabled) li a3, 9*SZREG-1 /* size must >= (word_copy stride + SZREG-1) */ bltu a2, a3, .Lbyte_copy_tail +#if !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) /* * Copy first bytes until dst is aligned to word boundary. * a0 - start of dst @@ -103,7 +104,7 @@ SYM_FUNC_START(fallback_scalar_usercopy_sum_enabled) /* a1 - start of src */ andi a3, a1, SZREG-1 bnez a3, .Lshift_copy - +#endif .Lword_copy: /* * Both src and dst are aligned, unrolled word copy @@ -137,6 +138,7 @@ SYM_FUNC_START(fallback_scalar_usercopy_sum_enabled) addi t0, t0, 8*SZREG /* revert to original value */ j .Lbyte_copy_tail +#if !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) .Lshift_copy: /* @@ -189,6 +191,7 @@ SYM_FUNC_START(fallback_scalar_usercopy_sum_enabled) /* Revert src to original unaligned value */ add a1, a1, a3 +#endif .Lbyte_copy_tail: /*