[PATCH net-next-2.6 v2] filter: optimize sk_run_filter

Eric Dumazet
2010-11-19T13:16:55Z

Le vendredi 19 novembre 2010 à 20:57 +0800, Changli Gao a écrit :
> On Fri, Nov 19, 2010 at 8:32 PM, Changli Gao <xiaosuo@gmail.com> wrote:
> >
> > you missed the users of sk_run_filter in directory dev/.
> >
>
> Sorry, the directory is drivers/.
>
>

You're right, thanks !

[PATCH net-next-2.6 v2] filter: optimize sk_run_filter

Remove pc variable to avoid arithmetic to compute fentry at each filter
instruction. Jumps directly manipulate fentry pointer.

As the last instruction of filter[] is guaranteed to be a RETURN, and
all jumps are before the last instruction, we dont need to check filter
bounds (number of instructions in filter array) at each iteration, so we
remove it from sk_run_filter() params.

On x86_32 remove f_k var introduced in commit 57fe93b374a6b871
(filter: make sure filters dont read uninitialized memory)

Note : We could use a CONFIG_ARCH_HAS_{FEW|MANY}_REGISTERS in order to
avoid too many ifdefs in this code.

This helps compiler to use cpu registers to hold fentry and A
accumulator.

On x86_32, this saves 401 bytes, and more important, sk_run_filter()
runs much faster because less register pressure (One less conditional
branch per BPF instruction)

# size net/core/filter.o net/core/filter_pre.o
text data bss dec hex filename
2948 0 0 2948 b84 net/core/filter.o
3349 0 0 3349 d15 net/core/filter_pre.o

on x86_64 :
# size net/core/filter.o net/core/filter_pre.o
text data bss dec hex filename
5173 0 0 5173 1435 net/core/filter.o
5224 0 0 5224 1468 net/core/filter_pre.o

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Changli Gao <xiaosuo@gmail.com>
Cc: Hagen Paul Pfeifer <hagen@jauu.net>
---
V2: add missing changes for drivers/isdn/i4l/isdn_ppp.c &
drivers/net/ppp_generic.c

drivers/isdn/i4l/isdn_ppp.c | 14 ++---
drivers/net/ppp_generic.c | 12 +---
include/linux/filter.h | 2
net/core/filter.c | 93 +++++++++++++++++-----------------
net/core/timestamping.c | 2
net/packet/af_packet.c | 2
6 files changed, 61 insertions(+), 64 deletions(-)

diff --git a/drivers/isdn/i4l/isdn_ppp.c b/drivers/isdn/i4l/isdn_ppp.c
index 97c5cc2..9e8162c 100644
--- a/drivers/isdn/i4l/isdn_ppp.c
+++ b/drivers/isdn/i4l/isdn_ppp.c
@@ -1147,15 +1147,14 @@ isdn_ppp_push_higher(isdn_net_dev * net_dev, isdn_net_local * lp, struct sk_buff
}

if (is->pass_filter
- && sk_run_filter(skb, is->pass_filter, is->pass_len) == 0) {
+ && sk_run_filter(skb, is->pass_filter) == 0) {
if (is->debug & 0x2)
printk(KERN_DEBUG "IPPP: inbound frame filtered.\n");
kfree_skb(skb);
return;
}
if (!(is->active_filter
- && sk_run_filter(skb, is->active_filter,
- is->active_len) == 0)) {
+ && sk_run_filter(skb, is->active_filter) == 0)) {
if (is->debug & 0x2)
printk(KERN_DEBUG "IPPP: link-active filter: reseting huptimer.\n");
lp->huptimer = 0;
@@ -1294,15 +1293,14 @@ isdn_ppp_xmit(struct sk_buff *skb, struct net_device *netdev)
}

if (ipt->pass_filter
- && sk_run_filter(skb, ipt->pass_filter, ipt->pass_len) == 0) {
+ && sk_run_filter(skb, ipt->pass_filter) == 0) {
if (ipt->debug & 0x4)
printk(KERN_DEBUG "IPPP: outbound frame filtered.\n");
kfree_skb(skb);
goto unlock;
}
if (!(ipt->active_filter
- && sk_run_filter(skb, ipt->active_filter,
- ipt->active_len) == 0)) {
+ && sk_run_filter(skb, ipt->active_filter) == 0)) {
if (ipt->debug & 0x4)
printk(KERN_DEBUG "IPPP: link-active filter: reseting huptimer.\n");
lp->huptimer = 0;
@@ -1492,9 +1490,9 @@ int isdn_ppp_autodial_filter(struct sk_buff *skb, isdn_net_local *lp)
}

drop |= is->pass_filter
- && sk_run_filter(skb, is->pass_filter, is->pass_len) == 0;
+ && sk_run_filter(skb, is->pass_filter) == 0;
drop |= is->active_filter
- && sk_run_filter(skb, is->active_filter, is->active_len) == 0;
+ && sk_run_filter(skb, is->active_filter) == 0;

skb_push(skb, IPPP_MAX_HEADER - 4);
return drop;
diff --git a/drivers/net/ppp_generic.c b/drivers/net/ppp_generic.c
index 09cf56d..0c91598a 100644
--- a/drivers/net/ppp_generic.c
+++ b/drivers/net/ppp_generic.c
@@ -1136,8 +1136,7 @@ ppp_send_frame(struct ppp *ppp, struct sk_buff *skb)
a four-byte PPP header on each packet */
*skb_push(skb, 2) = 1;
if (ppp->pass_filter &&
- sk_run_filter(skb, ppp->pass_filter,
- ppp->pass_len) == 0) {
+ sk_run_filter(skb, ppp->pass_filter) == 0) {
if (ppp->debug & 1)
printk(KERN_DEBUG "PPP: outbound frame not passed\n");
kfree_skb(skb);
@@ -1145,8 +1144,7 @@ ppp_send_frame(struct ppp *ppp, struct sk_buff *skb)
}
/* if this packet passes the active filter, record the time */
if (!(ppp->active_filter &&
- sk_run_filter(skb, ppp->active_filter,
- ppp->active_len) == 0))
+ sk_run_filter(skb, ppp->active_filter) == 0))
ppp->last_xmit = jiffies;
skb_pull(skb, 2);
#else
@@ -1758,8 +1756,7 @@ ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb)

*skb_push(skb, 2) = 0;
if (ppp->pass_filter &&
- sk_run_filter(skb, ppp->pass_filter,
- ppp->pass_len) == 0) {
+ sk_run_filter(skb, ppp->pass_filter) == 0) {
if (ppp->debug & 1)
printk(KERN_DEBUG "PPP: inbound frame "
"not passed\n");
@@ -1767,8 +1764,7 @@ ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb)
return;
}
if (!(ppp->active_filter &&
- sk_run_filter(skb, ppp->active_filter,
- ppp->active_len) == 0))
+ sk_run_filter(skb, ppp->active_filter) == 0))
ppp->last_recv = jiffies;
__skb_pull(skb, 2);
} else
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 151f5d7..447a775 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -147,7 +147,7 @@ struct sock;

extern int sk_filter(struct sock *sk, struct sk_buff *skb);
extern unsigned int sk_run_filter(struct sk_buff *skb,
- struct sock_filter *filter, int flen);
+ const struct sock_filter *filter);
extern int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk);
extern int sk_detach_filter(struct sock *sk);
extern int sk_chk_filter(struct sock_filter *filter, int flen);
diff --git a/net/core/filter.c b/net/core/filter.c
index 15a545d..9e77b3c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -137,7 +137,7 @@ int sk_filter(struct sock *sk, struct sk_buff *skb)
rcu_read_lock_bh();
filter = rcu_dereference_bh(sk->sk_filter);
if (filter) {
- unsigned int pkt_len = sk_run_filter(skb, filter->insns, filter->len);
+ unsigned int pkt_len = sk_run_filter(skb, filter->insns);

err = pkt_len ? pskb_trim(skb, pkt_len) : -EPERM;
}
@@ -151,14 +151,15 @@ EXPORT_SYMBOL(sk_filter);
* sk_run_filter - run a filter on a socket
* @skb: buffer to run the filter on
* @filter: filter to apply
- * @flen: length of filter
*
* Decode and apply filter instructions to the skb->data.
- * Return length to keep, 0 for none. skb is the data we are
- * filtering, filter is the array of filter instructions, and
- * len is the number of filter blocks in the array.
+ * Return length to keep, 0 for none. @skb is the data we are
+ * filtering, @filter is the array of filter instructions.
+ * Because all jumps are guaranteed to be before last instruction,
+ * and last instruction guaranteed to be a RET, we dont need to check
+ * flen. (We used to pass to this function the length of filter)
*/
-unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int flen)
+unsigned int sk_run_filter(struct sk_buff *skb, const struct sock_filter *fentry)
{
void *ptr;
u32 A = 0; /* Accumulator */
@@ -167,34 +168,36 @@ unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int
unsigned long memvalid = 0;
u32 tmp;
int k;
- int pc;

BUILD_BUG_ON(BPF_MEMWORDS > BITS_PER_LONG);
/*
* Process array of filter instructions.
*/
- for (pc = 0; pc < flen; pc++) {
- const struct sock_filter *fentry = &filter[pc];
- u32 f_k = fentry->k;
+ for (;; fentry++) {
+#if defined(CONFIG_X86_32)
+#define K (fentry->k)
+#else
+ const u32 K = fentry->k;
+#endif

switch (fentry->code) {
case BPF_S_ALU_ADD_X:
A += X;
continue;
case BPF_S_ALU_ADD_K:
- A += f_k;
+ A += K;
continue;
case BPF_S_ALU_SUB_X:
A -= X;
continue;
case BPF_S_ALU_SUB_K:
- A -= f_k;
+ A -= K;
continue;
case BPF_S_ALU_MUL_X:
A *= X;
continue;
case BPF_S_ALU_MUL_K:
- A *= f_k;
+ A *= K;
continue;
case BPF_S_ALU_DIV_X:
if (X == 0)
@@ -202,64 +205,64 @@ unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int
A /= X;
continue;
case BPF_S_ALU_DIV_K:
- A /= f_k;
+ A /= K;
continue;
case BPF_S_ALU_AND_X:
A &= X;
continue;
case BPF_S_ALU_AND_K:
- A &= f_k;
+ A &= K;
continue;
case BPF_S_ALU_OR_X:
A |= X;
continue;
case BPF_S_ALU_OR_K:
- A |= f_k;
+ A |= K;
continue;
case BPF_S_ALU_LSH_X:
A <<= X;
continue;
case BPF_S_ALU_LSH_K:
- A <<= f_k;
+ A <<= K;
continue;
case BPF_S_ALU_RSH_X:
A >>= X;
continue;
case BPF_S_ALU_RSH_K:
- A >>= f_k;
+ A >>= K;
continue;
case BPF_S_ALU_NEG:
A = -A;
continue;
case BPF_S_JMP_JA:
- pc += f_k;
+ fentry += K;
continue;
case BPF_S_JMP_JGT_K:
- pc += (A > f_k) ? fentry->jt : fentry->jf;
+ fentry += (A > K) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JGE_K:
- pc += (A >= f_k) ? fentry->jt : fentry->jf;
+ fentry += (A >= K) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JEQ_K:
- pc += (A == f_k) ? fentry->jt : fentry->jf;
+ fentry += (A == K) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JSET_K:
- pc += (A & f_k) ? fentry->jt : fentry->jf;
+ fentry += (A & K) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JGT_X:
- pc += (A > X) ? fentry->jt : fentry->jf;
+ fentry += (A > X) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JGE_X:
- pc += (A >= X) ? fentry->jt : fentry->jf;
+ fentry += (A >= X) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JEQ_X:
- pc += (A == X) ? fentry->jt : fentry->jf;
+ fentry += (A == X) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JSET_X:
- pc += (A & X) ? fentry->jt : fentry->jf;
+ fentry += (A & X) ? fentry->jt : fentry->jf;
continue;
case BPF_S_LD_W_ABS:
- k = f_k;
+ k = K;
load_w:
ptr = load_pointer(skb, k, 4, &tmp);
if (ptr != NULL) {
@@ -268,7 +271,7 @@ load_w:
}
break;
case BPF_S_LD_H_ABS:
- k = f_k;
+ k = K;
load_h:
ptr = load_pointer(skb, k, 2, &tmp);
if (ptr != NULL) {
@@ -277,7 +280,7 @@ load_h:
}
break;
case BPF_S_LD_B_ABS:
- k = f_k;
+ k = K;
load_b:
ptr = load_pointer(skb, k, 1, &tmp);
if (ptr != NULL) {
@@ -292,34 +295,34 @@ load_b:
X = skb->len;
continue;
case BPF_S_LD_W_IND:
- k = X + f_k;
+ k = X + K;
goto load_w;
case BPF_S_LD_H_IND:
- k = X + f_k;
+ k = X + K;
goto load_h;
case BPF_S_LD_B_IND:
- k = X + f_k;
+ k = X + K;
goto load_b;
case BPF_S_LDX_B_MSH:
- ptr = load_pointer(skb, f_k, 1, &tmp);
+ ptr = load_pointer(skb, K, 1, &tmp);
if (ptr != NULL) {
X = (*(u8 *)ptr & 0xf) << 2;
continue;
}
return 0;
case BPF_S_LD_IMM:
- A = f_k;
+ A = K;
continue;
case BPF_S_LDX_IMM:
- X = f_k;
+ X = K;
continue;
case BPF_S_LD_MEM:
- A = (memvalid & (1UL << f_k)) ?
- mem[f_k] : 0;
+ A = (memvalid & (1UL << K)) ?
+ mem[K] : 0;
continue;
case BPF_S_LDX_MEM:
- X = (memvalid & (1UL << f_k)) ?
- mem[f_k] : 0;
+ X = (memvalid & (1UL << K)) ?
+ mem[K] : 0;
continue;
case BPF_S_MISC_TAX:
X = A;
@@ -328,16 +331,16 @@ load_b:
A = X;
continue;
case BPF_S_RET_K:
- return f_k;
+ return K;
case BPF_S_RET_A:
return A;
case BPF_S_ST:
- memvalid |= 1UL << f_k;
- mem[f_k] = A;
+ memvalid |= 1UL << K;
+ mem[K] = A;
continue;
case BPF_S_STX:
- memvalid |= 1UL << f_k;
- mem[f_k] = X;
+ memvalid |= 1UL << K;
+ mem[K] = X;
continue;
default:
WARN_ON(1);
diff --git a/net/core/timestamping.c b/net/core/timestamping.c
index 0ae6c22..dac7ed6 100644
--- a/net/core/timestamping.c
+++ b/net/core/timestamping.c
@@ -31,7 +31,7 @@ static unsigned int classify(struct sk_buff *skb)
if (likely(skb->dev &&
skb->dev->phydev &&
skb->dev->phydev->drv))
- return sk_run_filter(skb, ptp_filter, ARRAY_SIZE(ptp_filter));
+ return sk_run_filter(skb, ptp_filter);
else
return PTP_CLASS_NONE;
}
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 2096456..b6372dd 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -519,7 +519,7 @@ static inline unsigned int run_filter(struct sk_buff *skb, struct sock *sk,
rcu_read_lock_bh();
filter = rcu_dereference_bh(sk->sk_filter);
if (filter != NULL)
- res = sk_run_filter(skb, filter->insns, filter->len);
+ res = sk_run_filter(skb, filter->insns);
rcu_read_unlock_bh();

return res;