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[bpf-next,v2,5/9] riscv, bpf: optimize BPF tail calls

Message ID 20191216091343.23260-6-bjorn.topel@gmail.com (mailing list archive)
State New, archived
Headers show
Series riscv: BPF JIT fix, optimizations and far jumps support | expand

Commit Message

Björn Töpel Dec. 16, 2019, 9:13 a.m. UTC 
Remove one addi, and instead use the offset part of jalr.

Signed-off-by: Björn Töpel <bjorn.topel@gmail.com>
---
 arch/riscv/net/bpf_jit_comp.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

Comments

Palmer Dabbelt Dec. 23, 2019, 6:29 p.m. UTC | #1 
On Mon, 16 Dec 2019 01:13:39 PST (-0800), Bjorn Topel wrote:
> Remove one addi, and instead use the offset part of jalr.
>
> Signed-off-by: Björn Töpel <bjorn.topel@gmail.com>
> ---
>  arch/riscv/net/bpf_jit_comp.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
> index 2fc0f24ad30f..8aa19c846881 100644
> --- a/arch/riscv/net/bpf_jit_comp.c
> +++ b/arch/riscv/net/bpf_jit_comp.c
> @@ -552,7 +552,7 @@ static int epilogue_offset(struct rv_jit_context *ctx)
>  	return (to - from) << 2;
>  }
>
> -static void __build_epilogue(u8 reg, struct rv_jit_context *ctx)
> +static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
>  {
>  	int stack_adjust = ctx->stack_size, store_offset = stack_adjust - 8;
>
> @@ -589,9 +589,11 @@ static void __build_epilogue(u8 reg, struct rv_jit_context *ctx)
>
>  	emit(rv_addi(RV_REG_SP, RV_REG_SP, stack_adjust), ctx);
>  	/* Set return value. */
> -	if (reg == RV_REG_RA)
> +	if (!is_tail_call)
>  		emit(rv_addi(RV_REG_A0, RV_REG_A5, 0), ctx);
> -	emit(rv_jalr(RV_REG_ZERO, reg, 0), ctx);
> +	emit(rv_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA,
> +		     is_tail_call ? 4 : 0), /* skip TCC init */
> +	     ctx);
>  }
>
>  /* return -1 or inverted cond */
> @@ -751,9 +753,8 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
>  	if (is_12b_check(off, insn))
>  		return -1;
>  	emit(rv_ld(RV_REG_T3, off, RV_REG_T2), ctx);
> -	emit(rv_addi(RV_REG_T3, RV_REG_T3, 4), ctx);
>  	emit(rv_addi(RV_REG_TCC, RV_REG_T1, 0), ctx);
> -	__build_epilogue(RV_REG_T3, ctx);
> +	__build_epilogue(true, ctx);
>  	return 0;
>  }
>
> @@ -1504,7 +1505,7 @@ static void build_prologue(struct rv_jit_context *ctx)
>
>  static void build_epilogue(struct rv_jit_context *ctx)
>  {
> -	__build_epilogue(RV_REG_RA, ctx);
> +	__build_epilogue(false, ctx);
>  }
>
>  static int build_body(struct rv_jit_context *ctx, bool extra_pass)

Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>
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Patch

diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
index 2fc0f24ad30f..8aa19c846881 100644
--- a/arch/riscv/net/bpf_jit_comp.c
+++ b/arch/riscv/net/bpf_jit_comp.c
@@ -552,7 +552,7 @@  static int epilogue_offset(struct rv_jit_context *ctx)
 	return (to - from) << 2;
 }
 
-static void __build_epilogue(u8 reg, struct rv_jit_context *ctx)
+static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
 {
 	int stack_adjust = ctx->stack_size, store_offset = stack_adjust - 8;
 
@@ -589,9 +589,11 @@  static void __build_epilogue(u8 reg, struct rv_jit_context *ctx)
 
 	emit(rv_addi(RV_REG_SP, RV_REG_SP, stack_adjust), ctx);
 	/* Set return value. */
-	if (reg == RV_REG_RA)
+	if (!is_tail_call)
 		emit(rv_addi(RV_REG_A0, RV_REG_A5, 0), ctx);
-	emit(rv_jalr(RV_REG_ZERO, reg, 0), ctx);
+	emit(rv_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA,
+		     is_tail_call ? 4 : 0), /* skip TCC init */
+	     ctx);
 }
 
 /* return -1 or inverted cond */
@@ -751,9 +753,8 @@  static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
 	if (is_12b_check(off, insn))
 		return -1;
 	emit(rv_ld(RV_REG_T3, off, RV_REG_T2), ctx);
-	emit(rv_addi(RV_REG_T3, RV_REG_T3, 4), ctx);
 	emit(rv_addi(RV_REG_TCC, RV_REG_T1, 0), ctx);
-	__build_epilogue(RV_REG_T3, ctx);
+	__build_epilogue(true, ctx);
 	return 0;
 }
 
@@ -1504,7 +1505,7 @@  static void build_prologue(struct rv_jit_context *ctx)
 
 static void build_epilogue(struct rv_jit_context *ctx)
 {
-	__build_epilogue(RV_REG_RA, ctx);
+	__build_epilogue(false, ctx);
 }
 
 static int build_body(struct rv_jit_context *ctx, bool extra_pass)