nfp: bpf: detect packet reads could be cached, enable the optimisation

This patch is the front end of this optimisation, it detects and marks
those packet reads that could be cached. Then the optimisation "backend"
will be activated automatically.
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -2964,6 +2964,120 @@ static void nfp_bpf_opt_ldst_gather(struct nfp_prog *nfp_prog)
 	}
 }
 
+static void nfp_bpf_opt_pkt_cache(struct nfp_prog *nfp_prog)
+{
+	struct nfp_insn_meta *meta, *range_node = NULL;
+	s16 range_start = 0, range_end = 0;
+	bool cache_avail = false;
+	struct bpf_insn *insn;
+	s32 range_ptr_off = 0;
+	u32 range_ptr_id = 0;
+
+	list_for_each_entry(meta, &nfp_prog->insns, l) {
+		if (meta->flags & FLAG_INSN_IS_JUMP_DST)
+			cache_avail = false;
+
+		if (meta->skip)
+			continue;
+
+		insn = &meta->insn;
+
+		if (is_mbpf_store_pkt(meta) ||
+		    insn->code == (BPF_JMP | BPF_CALL) ||
+		    is_mbpf_classic_store_pkt(meta) ||
+		    is_mbpf_classic_load(meta)) {
+			cache_avail = false;
+			continue;
+		}
+
+		if (!is_mbpf_load(meta))
+			continue;
+
+		if (meta->ptr.type != PTR_TO_PACKET || meta->ldst_gather_len) {
+			cache_avail = false;
+			continue;
+		}
+
+		if (!cache_avail) {
+			cache_avail = true;
+			if (range_node)
+				goto end_current_then_start_new;
+			goto start_new;
+		}
+
+		/* Check ID to make sure two reads share the same
+		 * variable offset against PTR_TO_PACKET, and check OFF
+		 * to make sure they also share the same constant
+		 * offset.
+		 *
+		 * OFFs don't really need to be the same, because they
+		 * are the constant offsets against PTR_TO_PACKET, so
+		 * for different OFFs, we could canonicalize them to
+		 * offsets against original packet pointer. We don't
+		 * support this.
+		 */
+		if (meta->ptr.id == range_ptr_id &&
+		    meta->ptr.off == range_ptr_off) {
+			s16 new_start = range_start;
+			s16 end, off = insn->off;
+			s16 new_end = range_end;
+			bool changed = false;
+
+			if (off < range_start) {
+				new_start = off;
+				changed = true;
+			}
+
+			end = off + BPF_LDST_BYTES(insn);
+			if (end > range_end) {
+				new_end = end;
+				changed = true;
+			}
+
+			if (!changed)
+				continue;
+
+			if (new_end - new_start <= 64) {
+				/* Install new range. */
+				range_start = new_start;
+				range_end = new_end;
+				continue;
+			}
+		}
+
+end_current_then_start_new:
+		range_node->pkt_cache.range_start = range_start;
+		range_node->pkt_cache.range_end = range_end;
+start_new:
+		range_node = meta;
+		range_node->pkt_cache.do_init = true;
+		range_ptr_id = range_node->ptr.id;
+		range_ptr_off = range_node->ptr.off;
+		range_start = insn->off;
+		range_end = insn->off + BPF_LDST_BYTES(insn);
+	}
+
+	if (range_node) {
+		range_node->pkt_cache.range_start = range_start;
+		range_node->pkt_cache.range_end = range_end;
+	}
+
+	list_for_each_entry(meta, &nfp_prog->insns, l) {
+		if (meta->skip)
+			continue;
+
+		if (is_mbpf_load_pkt(meta) && !meta->ldst_gather_len) {
+			if (meta->pkt_cache.do_init) {
+				range_start = meta->pkt_cache.range_start;
+				range_end = meta->pkt_cache.range_end;
+			} else {
+				meta->pkt_cache.range_start = range_start;
+				meta->pkt_cache.range_end = range_end;
+			}
+		}
+	}
+}
+
 static int nfp_bpf_optimize(struct nfp_prog *nfp_prog)
 {
 	nfp_bpf_opt_reg_init(nfp_prog);
@@ -2971,6 +3085,7 @@ static int nfp_bpf_optimize(struct nfp_prog *nfp_prog)
 	nfp_bpf_opt_ld_mask(nfp_prog);
 	nfp_bpf_opt_ld_shift(nfp_prog);
 	nfp_bpf_opt_ldst_gather(nfp_prog);
+	nfp_bpf_opt_pkt_cache(nfp_prog);
 
 	return 0;
 }

drivers/net/ethernet/netronome/nfp/bpf/main.h

@@ -278,6 +278,36 @@ static inline bool is_mbpf_store(const struct nfp_insn_meta *meta)
 	return (meta->insn.code & ~BPF_SIZE_MASK) == (BPF_STX | BPF_MEM);
 }
 
+static inline bool is_mbpf_load_pkt(const struct nfp_insn_meta *meta)
+{
+	return is_mbpf_load(meta) && meta->ptr.type == PTR_TO_PACKET;
+}
+
+static inline bool is_mbpf_store_pkt(const struct nfp_insn_meta *meta)
+{
+	return is_mbpf_store(meta) && meta->ptr.type == PTR_TO_PACKET;
+}
+
+static inline bool is_mbpf_classic_load(const struct nfp_insn_meta *meta)
+{
+	u8 code = meta->insn.code;
+
+	return BPF_CLASS(code) == BPF_LD &&
+	       (BPF_MODE(code) == BPF_ABS || BPF_MODE(code) == BPF_IND);
+}
+
+static inline bool is_mbpf_classic_store(const struct nfp_insn_meta *meta)
+{
+	u8 code = meta->insn.code;
+
+	return BPF_CLASS(code) == BPF_ST && BPF_MODE(code) == BPF_MEM;
+}
+
+static inline bool is_mbpf_classic_store_pkt(const struct nfp_insn_meta *meta)
+{
+	return is_mbpf_classic_store(meta) && meta->ptr.type == PTR_TO_PACKET;
+}
+
 /**
  * struct nfp_prog - nfp BPF program
  * @bpf: backpointer to the bpf app priv structure