diff options
| author | Hagen Paul Pfeifer <hagen@jauu.net> | 2010-06-19 17:05:36 +0000 |
|---|---|---|
| committer | Andi Kleen <ak@linux.intel.com> | 2010-12-14 23:40:17 +0100 |
| commit | 69caa40820b6f142cae5485bd61362bb1dfcc12c (patch) | |
| tree | 3ec00e38f0bc2847524ce2499c9492ded197ecba /include | |
| parent | 5cd63b34258b056b568b05582310e966aa65d2fd (diff) | |
net: optimize Berkeley Packet Filter (BPF) processing
Gcc is currenlty not in the ability to optimize the switch statement in
sk_run_filter() because of dense case labels. This patch replace the
OR'd labels with ordered sequenced case labels. The sk_chk_filter()
function is modified to patch/replace the original OPCODES in a
ordered but equivalent form. gcc is now in the ability to transform the
switch statement in sk_run_filter into a jump table of complexity O(1).
Until this patch gcc generates a sequence of conditional branches (O(n) of 567
byte .text segment size (arch x86_64):
7ff: 8b 06 mov (%rsi),%eax
801: 66 83 f8 35 cmp $0x35,%ax
805: 0f 84 d0 02 00 00 je adb <sk_run_filter+0x31d>
80b: 0f 87 07 01 00 00 ja 918 <sk_run_filter+0x15a>
811: 66 83 f8 15 cmp $0x15,%ax
815: 0f 84 c5 02 00 00 je ae0 <sk_run_filter+0x322>
81b: 77 73 ja 890 <sk_run_filter+0xd2>
81d: 66 83 f8 04 cmp $0x4,%ax
821: 0f 84 17 02 00 00 je a3e <sk_run_filter+0x280>
827: 77 29 ja 852 <sk_run_filter+0x94>
829: 66 83 f8 01 cmp $0x1,%ax
[...]
With the modification the compiler translate the switch statement into
the following jump table fragment:
7ff: 66 83 3e 2c cmpw $0x2c,(%rsi)
803: 0f 87 1f 02 00 00 ja a28 <sk_run_filter+0x26a>
809: 0f b7 06 movzwl (%rsi),%eax
80c: ff 24 c5 00 00 00 00 jmpq *0x0(,%rax,8)
813: 44 89 e3 mov %r12d,%ebx
816: e9 43 03 00 00 jmpq b5e <sk_run_filter+0x3a0>
81b: 41 89 dc mov %ebx,%r12d
81e: e9 3b 03 00 00 jmpq b5e <sk_run_filter+0x3a0>
Furthermore, I reordered the instructions to reduce cache line misses by
order the most common instruction to the start.
[AK: Added as dependency on next patch]
Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/filter.h | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/include/linux/filter.h b/include/linux/filter.h index 151f5d703b7e..69b43dbea6c6 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -91,6 +91,54 @@ struct sock_fprog { /* Required for SO_ATTACH_FILTER. */ #define BPF_TAX 0x00 #define BPF_TXA 0x80 +enum { + BPF_S_RET_K = 0, + BPF_S_RET_A, + BPF_S_ALU_ADD_K, + BPF_S_ALU_ADD_X, + BPF_S_ALU_SUB_K, + BPF_S_ALU_SUB_X, + BPF_S_ALU_MUL_K, + BPF_S_ALU_MUL_X, + BPF_S_ALU_DIV_X, + BPF_S_ALU_AND_K, + BPF_S_ALU_AND_X, + BPF_S_ALU_OR_K, + BPF_S_ALU_OR_X, + BPF_S_ALU_LSH_K, + BPF_S_ALU_LSH_X, + BPF_S_ALU_RSH_K, + BPF_S_ALU_RSH_X, + BPF_S_ALU_NEG, + BPF_S_LD_W_ABS, + BPF_S_LD_H_ABS, + BPF_S_LD_B_ABS, + BPF_S_LD_W_LEN, + BPF_S_LD_W_IND, + BPF_S_LD_H_IND, + BPF_S_LD_B_IND, + BPF_S_LD_IMM, + BPF_S_LDX_W_LEN, + BPF_S_LDX_B_MSH, + BPF_S_LDX_IMM, + BPF_S_MISC_TAX, + BPF_S_MISC_TXA, + BPF_S_ALU_DIV_K, + BPF_S_LD_MEM, + BPF_S_LDX_MEM, + BPF_S_ST, + BPF_S_STX, + BPF_S_JMP_JA, + BPF_S_JMP_JEQ_K, + BPF_S_JMP_JEQ_X, + BPF_S_JMP_JGE_K, + BPF_S_JMP_JGE_X, + BPF_S_JMP_JGT_K, + BPF_S_JMP_JGT_X, + BPF_S_JMP_JSET_K, + BPF_S_JMP_JSET_X, +}; + #ifndef BPF_MAXINSNS #define BPF_MAXINSNS 4096 #endif |