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Commit bb9b9f88 authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by David S. Miller
Browse files

bpf: Only set node->ref = 1 if it has not been set 



This patch writes 'node->ref = 1' only if node->ref is 0.
The number of lookups/s for a ~1M entries LRU map increased by
~30% (260097 to 343313).

Other writes on 'node->ref = 0' is not changed.  In those cases, the
same cache line has to be changed anyway.

First column: Size of the LRU hash
Second column: Number of lookups/s

Before:
> echo "$((2**20+1)): $(./map_perf_test 1024 1 $((2**20+1)) 10000000 | awk '{print $3}')"
1048577: 260097

After:
> echo "$((2**20+1)): $(./map_perf_test 1024 1 $((2**20+1)) 10000000 | awk '{print $3}')"
1048577: 343313

Signed-off-by: default avatarMartin KaFai Lau <kafai@fb.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent cc555421

kernel/bpf/bpf_lru_list.h

+2 −1
Original line number Diff line number Diff line
@@ -69,6 +69,7 @@ static inline void bpf_lru_node_set_ref(struct bpf_lru_node *node) 
	/* ref is an approximation on access frequency.  It does not

	 * have to be very accurate.  Hence, no protection is used.

	 */

	if (!node->ref)

		node->ref = 1;

}

kernel/bpf/hashtab.c

+6 −1
Original line number Diff line number Diff line
@@ -519,9 +519,14 @@ static u32 htab_lru_map_gen_lookup(struct bpf_map *map, 
{

	struct bpf_insn *insn = insn_buf;

	const int ret = BPF_REG_0;

	const int ref_reg = BPF_REG_1;



	*insn++ = BPF_EMIT_CALL((u64 (*)(u64, u64, u64, u64, u64))__htab_map_lookup_elem);

	*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 2);

	*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 4);

	*insn++ = BPF_LDX_MEM(BPF_B, ref_reg, ret,

			      offsetof(struct htab_elem, lru_node) +

			      offsetof(struct bpf_lru_node, ref));

	*insn++ = BPF_JMP_IMM(BPF_JNE, ref_reg, 0, 1);

	*insn++ = BPF_ST_MEM(BPF_B, ret,

			     offsetof(struct htab_elem, lru_node) +

			     offsetof(struct bpf_lru_node, ref),