From 9a90c83c09874a2fd03905ef0f73512c9de18799 Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Mon, 23 Oct 2017 11:58:10 -0700 Subject: [PATCH] nfp: bpf: optimize the RMW for stack accesses When we are performing unaligned stack accesses in the 32-64B window we have to do a read-modify-write cycle. E.g. for reading 8 bytes from address 17: 0: tmp = stack[16] 1: gprLo = tmp >> 8 2: tmp = stack[20] 3: gprLo |= tmp << 24 4: tmp = stack[20] 5: gprHi = tmp >> 8 6: tmp = stack[24] 7: gprHi |= tmp << 24 The load on line 4 is unnecessary, because tmp already contains data from stack[20]. For write we can optimize both loads and writebacks away. Signed-off-by: Jakub Kicinski Reviewed-by: Quentin Monnet Signed-off-by: David S. Miller --- drivers/net/ethernet/netronome/nfp/bpf/jit.c | 33 +++++++++++++++----- 1 file changed, 25 insertions(+), 8 deletions(-) diff --git a/drivers/net/ethernet/netronome/nfp/bpf/jit.c b/drivers/net/ethernet/netronome/nfp/bpf/jit.c index 094acea35326..6730690cf9d8 100644 --- a/drivers/net/ethernet/netronome/nfp/bpf/jit.c +++ b/drivers/net/ethernet/netronome/nfp/bpf/jit.c @@ -644,11 +644,11 @@ data_st_host_order(struct nfp_prog *nfp_prog, u8 dst_gpr, swreg offset, typedef int (*lmem_step)(struct nfp_prog *nfp_prog, u8 gpr, u8 gpr_byte, s32 off, - unsigned int size, bool new_gpr); + unsigned int size, bool first, bool new_gpr, bool last); static int wrp_lmem_load(struct nfp_prog *nfp_prog, u8 dst, u8 dst_byte, s32 off, - unsigned int size, bool new_gpr) + unsigned int size, bool first, bool new_gpr, bool last) { u32 idx, src_byte; enum shf_sc sc; @@ -692,7 +692,13 @@ wrp_lmem_load(struct nfp_prog *nfp_prog, u8 dst, u8 dst_byte, s32 off, reg = reg_lm(0, idx); } else { reg = imm_a(nfp_prog); - wrp_mov(nfp_prog, reg, reg_lm(0, idx)); + /* If it's not the first part of the load and we start a new GPR + * that means we are loading a second part of the LMEM word into + * a new GPR. IOW we've already looked that LMEM word and + * therefore it has been loaded into imm_a(). + */ + if (first || !new_gpr) + wrp_mov(nfp_prog, reg, reg_lm(0, idx)); } emit_ld_field_any(nfp_prog, reg_both(dst), mask, reg, sc, shf, new_gpr); @@ -702,7 +708,7 @@ wrp_lmem_load(struct nfp_prog *nfp_prog, u8 dst, u8 dst_byte, s32 off, static int wrp_lmem_store(struct nfp_prog *nfp_prog, u8 src, u8 src_byte, s32 off, - unsigned int size, bool new_gpr) + unsigned int size, bool first, bool new_gpr, bool last) { u32 idx, dst_byte; enum shf_sc sc; @@ -746,13 +752,19 @@ wrp_lmem_store(struct nfp_prog *nfp_prog, u8 src, u8 src_byte, s32 off, reg = reg_lm(0, idx); } else { reg = imm_a(nfp_prog); - wrp_mov(nfp_prog, reg, reg_lm(0, idx)); + /* Only first and last LMEM locations are going to need RMW, + * the middle location will be overwritten fully. + */ + if (first || last) + wrp_mov(nfp_prog, reg, reg_lm(0, idx)); } emit_ld_field(nfp_prog, reg, mask, reg_b(src), sc, shf); - if (idx > RE_REG_LM_IDX_MAX) - wrp_mov(nfp_prog, reg_lm(0, idx), reg); + if (new_gpr || last) { + if (idx > RE_REG_LM_IDX_MAX) + wrp_mov(nfp_prog, reg_lm(0, idx), reg); + } return 0; } @@ -762,6 +774,7 @@ mem_op_stack(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta, unsigned int size, u8 gpr, bool clr_gpr, lmem_step step) { s32 off = nfp_prog->stack_depth + meta->insn.off; + bool first = true, last; u8 prev_gpr = 255; u32 gpr_byte = 0; int ret; @@ -777,12 +790,16 @@ mem_op_stack(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta, slice_end = min(off + slice_size, round_up(off + 1, 4)); slice_size = slice_end - off; + last = slice_size == size; + ret = step(nfp_prog, gpr, gpr_byte, off, slice_size, - gpr != prev_gpr); + first, gpr != prev_gpr, last); if (ret) return ret; prev_gpr = gpr; + first = false; + gpr_byte += slice_size; if (gpr_byte >= 4) { gpr_byte -= 4; -- 2.45.2