linux-kernel - [PATCH bpf-next] arm64: bpf: optimize modulo operation

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Message-ID: <20190902061448.28252-1-jerinj@marvell.com>
Date:   Mon, 2 Sep 2019 11:44:48 +0530
From:   <jerinj@...vell.com>
To:     <netdev@...r.kernel.org>, Daniel Borkmann <daniel@...earbox.net>,
        "Alexei Starovoitov" <ast@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        "Catalin Marinas" <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "Martin KaFai Lau" <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        "open list:BPF JIT for ARM64" <bpf@...r.kernel.org>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
CC:     Jerin Jacob <jerinj@...vell.com>
Subject: [PATCH bpf-next] arm64: bpf: optimize modulo operation

From: Jerin Jacob <jerinj@...vell.com>

Optimize modulo operation instruction generation by
using single MSUB instruction vs MUL followed by SUB
instruction scheme.

Signed-off-by: Jerin Jacob <jerinj@...vell.com>
---
 arch/arm64/net/bpf_jit.h      | 3 +++
 arch/arm64/net/bpf_jit_comp.c | 6 ++----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/net/bpf_jit.h b/arch/arm64/net/bpf_jit.h
index cb7ab50b7657..eb73f9f72c46 100644
--- a/arch/arm64/net/bpf_jit.h
+++ b/arch/arm64/net/bpf_jit.h
@@ -171,6 +171,9 @@
 /* Rd = Ra + Rn * Rm */
 #define A64_MADD(sf, Rd, Ra, Rn, Rm) aarch64_insn_gen_data3(Rd, Ra, Rn, Rm, \
 	A64_VARIANT(sf), AARCH64_INSN_DATA3_MADD)
+/* Rd = Ra - Rn * Rm */
+#define A64_MSUB(sf, Rd, Ra, Rn, Rm) aarch64_insn_gen_data3(Rd, Ra, Rn, Rm, \
+	A64_VARIANT(sf), AARCH64_INSN_DATA3_MSUB)
 /* Rd = Rn * Rm */
 #define A64_MUL(sf, Rd, Rn, Rm) A64_MADD(sf, Rd, A64_ZR, Rn, Rm)
 
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index f5b437f8a22b..cdc79de0c794 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -409,8 +409,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 			break;
 		case BPF_MOD:
 			emit(A64_UDIV(is64, tmp, dst, src), ctx);
-			emit(A64_MUL(is64, tmp, tmp, src), ctx);
-			emit(A64_SUB(is64, dst, dst, tmp), ctx);
+			emit(A64_MSUB(is64, dst, dst, tmp, src), ctx);
 			break;
 		}
 		break;
@@ -516,8 +515,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 	case BPF_ALU64 | BPF_MOD | BPF_K:
 		emit_a64_mov_i(is64, tmp2, imm, ctx);
 		emit(A64_UDIV(is64, tmp, dst, tmp2), ctx);
-		emit(A64_MUL(is64, tmp, tmp, tmp2), ctx);
-		emit(A64_SUB(is64, dst, dst, tmp), ctx);
+		emit(A64_MSUB(is64, dst, dst, tmp, tmp2), ctx);
 		break;
 	case BPF_ALU | BPF_LSH | BPF_K:
 	case BPF_ALU64 | BPF_LSH | BPF_K:
-- 
2.23.0