linux-kernel - [RFC PATCH v8 20/21] riscv: Optimize task switch codes of vector

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Date:   Thu,  9 Sep 2021 01:45:32 +0800
From:   Greentime Hu <greentime.hu@...ive.com>
To:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        aou@...s.berkeley.edu, palmer@...belt.com,
        paul.walmsley@...ive.com, vincent.chen@...ive.com
Subject: [RFC PATCH v8 20/21] riscv: Optimize task switch codes of vector

This patch replacees 2 instructions with 1 instruction to do the same thing
. rs1=x0 with rd != x0 is a special form of the instruction that sets vl to
MAXVL.

Suggested-by: Andrew Waterman <andrew@...ive.com>
Co-developed-by: Vincent Chen <vincent.chen@...ive.com>
Signed-off-by: Vincent Chen <vincent.chen@...ive.com>
Signed-off-by: Greentime Hu <greentime.hu@...ive.com>
---
 arch/riscv/kernel/vector.S | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/kernel/vector.S b/arch/riscv/kernel/vector.S
index 4f0c5a166e4e..f7223c81b11a 100644
--- a/arch/riscv/kernel/vector.S
+++ b/arch/riscv/kernel/vector.S
@@ -27,8 +27,7 @@
 #define x_vl     t2
 #define x_vcsr   t3
 #define incr     t4
-#define m_one    t5
-#define status   t6
+#define status   t5
 
 ENTRY(__vstate_save)
 	li      status, SR_VS
@@ -38,8 +37,7 @@ ENTRY(__vstate_save)
 	csrr    x_vtype, CSR_VTYPE
 	csrr    x_vl, CSR_VL
 	csrr    x_vcsr, CSR_VCSR
-	li      m_one, -1
-	vsetvli incr, m_one, e8, m8
+	vsetvli incr, x0, e8, m8
 	vse8.v   v0, (datap)
 	add     datap, datap, incr
 	vse8.v   v8, (datap)
@@ -61,8 +59,7 @@ ENTRY(__vstate_restore)
 	li      status, SR_VS
 	csrs    CSR_STATUS, status
 
-	li      m_one, -1
-	vsetvli incr, m_one, e8, m8
+	vsetvli incr, x0, e8, m8
 	vle8.v   v0, (datap)
 	add     datap, datap, incr
 	vle8.v   v8, (datap)
-- 
2.31.1