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Commit 9fb410a8 authored by Jiong Wang's avatar Jiong Wang Committed by Daniel Borkmann
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nfp: bpf: migrate to advanced reciprocal divide in reciprocal_div.h 



As we are doing JIT, we would want to use the advanced version of the
reciprocal divide (reciprocal_value_adv) to trade performance with host.

We could reduce the required ALU instructions from 4 to 2 or 1.

Signed-off-by: default avatarJiong Wang <jiong.wang@netronome.com>
Reviewed-by: default avatarJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 2a952b03

drivers/net/ethernet/netronome/nfp/bpf/jit.c

+53 −11
Original line number Diff line number Diff line
@@ -1497,8 +1497,8 @@ wrp_mul(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta, 
static int wrp_div_imm(struct nfp_prog *nfp_prog, u8 dst, u64 imm)

{

	swreg dst_both = reg_both(dst), dst_a = reg_a(dst), dst_b = reg_a(dst);

	struct reciprocal_value rvalue;

	swreg tmp_b = imm_b(nfp_prog);

	struct reciprocal_value_adv rvalue;

	u8 pre_shift, exp;

	swreg magic;



	if (imm > U32_MAX) {
@@ -1506,16 +1506,58 @@ static int wrp_div_imm(struct nfp_prog *nfp_prog, u8 dst, u64 imm) 
		return 0;

	}



	rvalue = reciprocal_value(imm);

	/* NOTE: because we are using "reciprocal_value_adv" which doesn't

	 * support "divisor > (1u << 31)", we need to JIT separate NFP sequence

	 * to handle such case which actually equals to the result of unsigned

	 * comparison "dst >= imm" which could be calculated using the following

	 * NFP sequence:

	 *

	 *  alu[--, dst, -, imm]

	 *  immed[imm, 0]

	 *  alu[dst, imm, +carry, 0]

	 *

	 */

	if (imm > 1U << 31) {

		swreg tmp_b = ur_load_imm_any(nfp_prog, imm, imm_b(nfp_prog));



		emit_alu(nfp_prog, reg_none(), dst_a, ALU_OP_SUB, tmp_b);

		wrp_immed(nfp_prog, imm_a(nfp_prog), 0);

		emit_alu(nfp_prog, dst_both, imm_a(nfp_prog), ALU_OP_ADD_C,

			 reg_imm(0));

		return 0;

	}



	rvalue = reciprocal_value_adv(imm, 32);

	exp = rvalue.exp;

	if (rvalue.is_wide_m && !(imm & 1)) {

		pre_shift = fls(imm & -imm) - 1;

		rvalue = reciprocal_value_adv(imm >> pre_shift, 32 - pre_shift);

	} else {

		pre_shift = 0;

	}

	magic = ur_load_imm_any(nfp_prog, rvalue.m, imm_b(nfp_prog));

	wrp_mul_u32(nfp_prog, imm_both(nfp_prog), reg_none(), dst_a, magic,

		    true);

	emit_alu(nfp_prog, dst_both, dst_a, ALU_OP_SUB, tmp_b);

	if (imm == 1U << exp) {

		emit_shf(nfp_prog, dst_both, reg_none(), SHF_OP_NONE, dst_b,

		 SHF_SC_R_SHF, rvalue.sh1);

	emit_alu(nfp_prog, dst_both, dst_a, ALU_OP_ADD, tmp_b);

			 SHF_SC_R_SHF, exp);

	} else if (rvalue.is_wide_m) {

		wrp_mul_u32(nfp_prog, imm_both(nfp_prog), reg_none(), dst_a,

			    magic, true);

		emit_alu(nfp_prog, dst_both, dst_a, ALU_OP_SUB,

			 imm_b(nfp_prog));

		emit_shf(nfp_prog, dst_both, reg_none(), SHF_OP_NONE, dst_b,

		 SHF_SC_R_SHF, rvalue.sh2);

			 SHF_SC_R_SHF, 1);

		emit_alu(nfp_prog, dst_both, dst_a, ALU_OP_ADD,

			 imm_b(nfp_prog));

		emit_shf(nfp_prog, dst_both, reg_none(), SHF_OP_NONE, dst_b,

			 SHF_SC_R_SHF, rvalue.sh - 1);

	} else {

		if (pre_shift)

			emit_shf(nfp_prog, dst_both, reg_none(), SHF_OP_NONE,

				 dst_b, SHF_SC_R_SHF, pre_shift);

		wrp_mul_u32(nfp_prog, dst_both, reg_none(), dst_a, magic, true);

		emit_shf(nfp_prog, dst_both, reg_none(), SHF_OP_NONE,

			 dst_b, SHF_SC_R_SHF, rvalue.sh);

	}



	return 0;

}