[RFC PATCH v8 20/21] riscv: Optimize task switch codes of vector
Jisheng Zhang
jszhang3 at mail.ustc.edu.cn
Wed Sep 15 07:29:37 PDT 2021
On Thu, 9 Sep 2021 01:45:32 +0800
Greentime Hu <greentime.hu at sifive.com> wrote:
> 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.
Similarly, the vector.S is newly introduced in this patch set, so could
this optimization be folded into the __vstate_save and __vstate_restore
introduction patch? Or it's better to keep this optimizaion in commit log?
>
> Suggested-by: Andrew Waterman <andrew at sifive.com>
> Co-developed-by: Vincent Chen <vincent.chen at sifive.com>
> Signed-off-by: Vincent Chen <vincent.chen at sifive.com>
> Signed-off-by: Greentime Hu <greentime.hu at sifive.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)
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