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net: optimize Berkeley Packet Filter (BPF) processing

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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.

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Hagen Paul Pfeifer 2010-06-19 17:05:36 +00:00 committed by David S. Miller
parent bd97a63f7d
commit 01f2f3f6ef
2 changed files with 213 additions and 55 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
include/linux/filter.h
View File

@ -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

220
net/core/filter.c
View File

@ -128,87 +128,87 @@ unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int
fentry = &filter[pc];
switch (fentry->code) {
case BPF_ALU|BPF_ADD|BPF_X:
case BPF_S_ALU_ADD_X:
A += X;
continue;
case BPF_ALU|BPF_ADD|BPF_K:
case BPF_S_ALU_ADD_K:
A += fentry->k;
continue;
case BPF_ALU|BPF_SUB|BPF_X:
case BPF_S_ALU_SUB_X:
A -= X;
continue;
case BPF_ALU|BPF_SUB|BPF_K:
case BPF_S_ALU_SUB_K:
A -= fentry->k;
continue;
case BPF_ALU|BPF_MUL|BPF_X:
case BPF_S_ALU_MUL_X:
A *= X;
continue;
case BPF_ALU|BPF_MUL|BPF_K:
case BPF_S_ALU_MUL_K:
A *= fentry->k;
continue;
case BPF_ALU|BPF_DIV|BPF_X:
case BPF_S_ALU_DIV_X:
if (X == 0)
return 0;
A /= X;
continue;
case BPF_ALU|BPF_DIV|BPF_K:
case BPF_S_ALU_DIV_K:
A /= fentry->k;
continue;
case BPF_ALU|BPF_AND|BPF_X:
case BPF_S_ALU_AND_X:
A &= X;
continue;
case BPF_ALU|BPF_AND|BPF_K:
case BPF_S_ALU_AND_K:
A &= fentry->k;
continue;
case BPF_ALU|BPF_OR|BPF_X:
case BPF_S_ALU_OR_X:
A |= X;
continue;
case BPF_ALU|BPF_OR|BPF_K:
case BPF_S_ALU_OR_K:
A |= fentry->k;
continue;
case BPF_ALU|BPF_LSH|BPF_X:
case BPF_S_ALU_LSH_X:
A <<= X;
continue;
case BPF_ALU|BPF_LSH|BPF_K:
case BPF_S_ALU_LSH_K:
A <<= fentry->k;
continue;
case BPF_ALU|BPF_RSH|BPF_X:
case BPF_S_ALU_RSH_X:
A >>= X;
continue;
case BPF_ALU|BPF_RSH|BPF_K:
case BPF_S_ALU_RSH_K:
A >>= fentry->k;
continue;
case BPF_ALU|BPF_NEG:
case BPF_S_ALU_NEG:
A = -A;
continue;
case BPF_JMP|BPF_JA:
case BPF_S_JMP_JA:
pc += fentry->k;
continue;
case BPF_JMP|BPF_JGT|BPF_K:
case BPF_S_JMP_JGT_K:
pc += (A > fentry->k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JGE|BPF_K:
case BPF_S_JMP_JGE_K:
pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JEQ|BPF_K:
case BPF_S_JMP_JEQ_K:
pc += (A == fentry->k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JSET|BPF_K:
case BPF_S_JMP_JSET_K:
pc += (A & fentry->k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JGT|BPF_X:
case BPF_S_JMP_JGT_X:
pc += (A > X) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JGE|BPF_X:
case BPF_S_JMP_JGE_X:
pc += (A >= X) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JEQ|BPF_X:
case BPF_S_JMP_JEQ_X:
pc += (A == X) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JSET|BPF_X:
case BPF_S_JMP_JSET_X:
pc += (A & X) ? fentry->jt : fentry->jf;
continue;
case BPF_LD|BPF_W|BPF_ABS:
case BPF_S_LD_W_ABS:
k = fentry->k;
load_w:
ptr = load_pointer(skb, k, 4, &tmp);
@ -217,7 +217,7 @@ load_w:
continue;
}
break;
case BPF_LD|BPF_H|BPF_ABS:
case BPF_S_LD_H_ABS:
k = fentry->k;
load_h:
ptr = load_pointer(skb, k, 2, &tmp);
@ -226,7 +226,7 @@ load_h:
continue;
}
break;
case BPF_LD|BPF_B|BPF_ABS:
case BPF_S_LD_B_ABS:
k = fentry->k;
load_b:
ptr = load_pointer(skb, k, 1, &tmp);
@ -235,54 +235,54 @@ load_b:
continue;
}
break;
case BPF_LD|BPF_W|BPF_LEN:
case BPF_S_LD_W_LEN:
A = skb->len;
continue;
case BPF_LDX|BPF_W|BPF_LEN:
case BPF_S_LDX_W_LEN:
X = skb->len;
continue;
case BPF_LD|BPF_W|BPF_IND:
case BPF_S_LD_W_IND:
k = X + fentry->k;
goto load_w;
case BPF_LD|BPF_H|BPF_IND:
case BPF_S_LD_H_IND:
k = X + fentry->k;
goto load_h;
case BPF_LD|BPF_B|BPF_IND:
case BPF_S_LD_B_IND:
k = X + fentry->k;
goto load_b;
case BPF_LDX|BPF_B|BPF_MSH:
case BPF_S_LDX_B_MSH:
ptr = load_pointer(skb, fentry->k, 1, &tmp);
if (ptr != NULL) {
X = (*(u8 *)ptr & 0xf) << 2;
continue;
}
return 0;
case BPF_LD|BPF_IMM:
case BPF_S_LD_IMM:
A = fentry->k;
continue;
case BPF_LDX|BPF_IMM:
case BPF_S_LDX_IMM:
X = fentry->k;
continue;
case BPF_LD|BPF_MEM:
case BPF_S_LD_MEM:
A = mem[fentry->k];
continue;
case BPF_LDX|BPF_MEM:
case BPF_S_LDX_MEM:
X = mem[fentry->k];
continue;
case BPF_MISC|BPF_TAX:
case BPF_S_MISC_TAX:
X = A;
continue;
case BPF_MISC|BPF_TXA:
case BPF_S_MISC_TXA:
A = X;
continue;
case BPF_RET|BPF_K:
case BPF_S_RET_K:
return fentry->k;
case BPF_RET|BPF_A:
case BPF_S_RET_A:
return A;
case BPF_ST:
case BPF_S_ST:
mem[fentry->k] = A;
continue;
case BPF_STX:
case BPF_S_STX:
mem[fentry->k] = X;
continue;
default:
@ -390,53 +390,128 @@ int sk_chk_filter(struct sock_filter *filter, int flen)
/* Only allow valid instructions */
switch (ftest->code) {
case BPF_ALU|BPF_ADD|BPF_K:
ftest->code = BPF_S_ALU_ADD_K;
break;
case BPF_ALU|BPF_ADD|BPF_X:
ftest->code = BPF_S_ALU_ADD_X;
break;
case BPF_ALU|BPF_SUB|BPF_K:
ftest->code = BPF_S_ALU_SUB_K;
break;
case BPF_ALU|BPF_SUB|BPF_X:
ftest->code = BPF_S_ALU_SUB_X;
break;
case BPF_ALU|BPF_MUL|BPF_K:
ftest->code = BPF_S_ALU_MUL_K;
break;
case BPF_ALU|BPF_MUL|BPF_X:
ftest->code = BPF_S_ALU_MUL_X;
break;
case BPF_ALU|BPF_DIV|BPF_X:
ftest->code = BPF_S_ALU_DIV_X;
break;
case BPF_ALU|BPF_AND|BPF_K:
ftest->code = BPF_S_ALU_AND_K;
break;
case BPF_ALU|BPF_AND|BPF_X:
ftest->code = BPF_S_ALU_AND_X;
break;
case BPF_ALU|BPF_OR|BPF_K:
ftest->code = BPF_S_ALU_OR_K;
break;
case BPF_ALU|BPF_OR|BPF_X:
ftest->code = BPF_S_ALU_OR_X;
break;
case BPF_ALU|BPF_LSH|BPF_K:
ftest->code = BPF_S_ALU_LSH_K;
break;
case BPF_ALU|BPF_LSH|BPF_X:
ftest->code = BPF_S_ALU_LSH_X;
break;
case BPF_ALU|BPF_RSH|BPF_K:
ftest->code = BPF_S_ALU_RSH_K;
break;
case BPF_ALU|BPF_RSH|BPF_X:
ftest->code = BPF_S_ALU_RSH_X;
break;
case BPF_ALU|BPF_NEG:
ftest->code = BPF_S_ALU_NEG;
break;
case BPF_LD|BPF_W|BPF_ABS:
ftest->code = BPF_S_LD_W_ABS;
break;
case BPF_LD|BPF_H|BPF_ABS:
ftest->code = BPF_S_LD_H_ABS;
break;
case BPF_LD|BPF_B|BPF_ABS:
ftest->code = BPF_S_LD_B_ABS;
break;
case BPF_LD|BPF_W|BPF_LEN:
ftest->code = BPF_S_LD_W_LEN;
break;
case BPF_LD|BPF_W|BPF_IND:
ftest->code = BPF_S_LD_W_IND;
break;
case BPF_LD|BPF_H|BPF_IND:
ftest->code = BPF_S_LD_H_IND;
break;
case BPF_LD|BPF_B|BPF_IND:
ftest->code = BPF_S_LD_B_IND;
break;
case BPF_LD|BPF_IMM:
ftest->code = BPF_S_LD_IMM;
break;
case BPF_LDX|BPF_W|BPF_LEN:
ftest->code = BPF_S_LDX_W_LEN;
break;
case BPF_LDX|BPF_B|BPF_MSH:
ftest->code = BPF_S_LDX_B_MSH;
break;
case BPF_LDX|BPF_IMM:
ftest->code = BPF_S_LDX_IMM;
break;
case BPF_MISC|BPF_TAX:
ftest->code = BPF_S_MISC_TAX;
break;
case BPF_MISC|BPF_TXA:
ftest->code = BPF_S_MISC_TXA;
break;
case BPF_RET|BPF_K:
ftest->code = BPF_S_RET_K;
break;
case BPF_RET|BPF_A:
ftest->code = BPF_S_RET_A;
break;
/* Some instructions need special checks */
case BPF_ALU|BPF_DIV|BPF_K:
/* check for division by zero */
case BPF_ALU|BPF_DIV|BPF_K:
if (ftest->k == 0)
return -EINVAL;
ftest->code = BPF_S_ALU_DIV_K;
break;
/* check for invalid memory addresses */
case BPF_LD|BPF_MEM:
case BPF_LDX|BPF_MEM:
case BPF_ST:
case BPF_STX:
/* check for invalid memory addresses */
if (ftest->k >= BPF_MEMWORDS)
return -EINVAL;
ftest->code = BPF_S_LD_MEM;
break;
case BPF_LDX|BPF_MEM:
if (ftest->k >= BPF_MEMWORDS)
return -EINVAL;
ftest->code = BPF_S_LDX_MEM;
break;
case BPF_ST:
if (ftest->k >= BPF_MEMWORDS)
return -EINVAL;
ftest->code = BPF_S_ST;
break;
case BPF_STX:
if (ftest->k >= BPF_MEMWORDS)
return -EINVAL;
ftest->code = BPF_S_STX;
break;
case BPF_JMP|BPF_JA:
@ -447,28 +522,63 @@ int sk_chk_filter(struct sock_filter *filter, int flen)
*/
if (ftest->k >= (unsigned)(flen-pc-1))
return -EINVAL;
ftest->code = BPF_S_JMP_JA;
break;
case BPF_JMP|BPF_JEQ|BPF_K:
ftest->code = BPF_S_JMP_JEQ_K;
break;
case BPF_JMP|BPF_JEQ|BPF_X:
ftest->code = BPF_S_JMP_JEQ_X;
break;
case BPF_JMP|BPF_JGE|BPF_K:
ftest->code = BPF_S_JMP_JGE_K;
break;
case BPF_JMP|BPF_JGE|BPF_X:
ftest->code = BPF_S_JMP_JGE_X;
break;
case BPF_JMP|BPF_JGT|BPF_K:
ftest->code = BPF_S_JMP_JGT_K;
break;
case BPF_JMP|BPF_JGT|BPF_X:
ftest->code = BPF_S_JMP_JGT_X;
break;
case BPF_JMP|BPF_JSET|BPF_K:
ftest->code = BPF_S_JMP_JSET_K;
break;
case BPF_JMP|BPF_JSET|BPF_X:
/* for conditionals both must be safe */
if (pc + ftest->jt + 1 >= flen ||
pc + ftest->jf + 1 >= flen)
return -EINVAL;
ftest->code = BPF_S_JMP_JSET_X;
break;
default:
return -EINVAL;
}
/* for conditionals both must be safe */
switch (ftest->code) {
case BPF_S_JMP_JEQ_K:
case BPF_S_JMP_JEQ_X:
case BPF_S_JMP_JGE_K:
case BPF_S_JMP_JGE_X:
case BPF_S_JMP_JGT_K:
case BPF_S_JMP_JGT_X:
case BPF_S_JMP_JSET_X:
case BPF_S_JMP_JSET_K:
if (pc + ftest->jt + 1 >= flen ||
pc + ftest->jf + 1 >= flen)
return -EINVAL;
}
}
return (BPF_CLASS(filter[flen - 1].code) == BPF_RET) ? 0 : -EINVAL;
/* last instruction must be a RET code */
switch (filter[flen - 1].code) {
case BPF_S_RET_K:
case BPF_S_RET_A:
return 0;
break;
default:
return -EINVAL;
}
}
EXPORT_SYMBOL(sk_chk_filter);