Commit d826eb14 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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ipv4: PKTINFO doesnt need dst reference



Le lundi 07 novembre 2011 à 15:33 +0100, Eric Dumazet a écrit :

> At least, in recent kernels we dont change dst->refcnt in forwarding
> patch (usinf NOREF skb->dst)
>
> One particular point is the atomic_inc(dst->refcnt) we have to perform
> when queuing an UDP packet if socket asked PKTINFO stuff (for example a
> typical DNS server has to setup this option)
>
> I have one patch somewhere that stores the information in skb->cb[] and
> avoid the atomic_{inc|dec}(dst->refcnt).
>

OK I found it, I did some extra tests and believe its ready.

[PATCH net-next] ipv4: IP_PKTINFO doesnt need dst reference

When a socket uses IP_PKTINFO notifications, we currently force a dst
reference for each received skb. Reader has to access dst to get needed
information (rt_iif & rt_spec_dst) and must release dst reference.

We also forced a dst reference if skb was put in socket backlog, even
without IP_PKTINFO handling. This happens under stress/load.

We can instead store the needed information in skb->cb[], so that only
softirq handler really access dst, improving cache hit ratios.

This removes two atomic operations per packet, and false sharing as
well.

On a benchmark using a mono threaded receiver (doing only recvmsg()
calls), I can reach 720.000 pps instead of 570.000 pps.

IP_PKTINFO is typically used by DNS servers, and any multihomed aware
UDP application.
Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent acb32ba3
......@@ -450,7 +450,7 @@ extern int ip_options_rcv_srr(struct sk_buff *skb);
* Functions provided by ip_sockglue.c
*/
extern int ip_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
extern void ipv4_pktinfo_prepare(struct sk_buff *skb);
extern void ip_cmsg_recv(struct msghdr *msg, struct sk_buff *skb);
extern int ip_cmsg_send(struct net *net,
struct msghdr *msg, struct ipcm_cookie *ipc);
......
......@@ -55,20 +55,13 @@
/*
* SOL_IP control messages.
*/
#define PKTINFO_SKB_CB(__skb) ((struct in_pktinfo *)((__skb)->cb))
static void ip_cmsg_recv_pktinfo(struct msghdr *msg, struct sk_buff *skb)
{
struct in_pktinfo info;
struct rtable *rt = skb_rtable(skb);
struct in_pktinfo info = *PKTINFO_SKB_CB(skb);
info.ipi_addr.s_addr = ip_hdr(skb)->daddr;
if (rt) {
info.ipi_ifindex = rt->rt_iif;
info.ipi_spec_dst.s_addr = rt->rt_spec_dst;
} else {
info.ipi_ifindex = 0;
info.ipi_spec_dst.s_addr = 0;
}
put_cmsg(msg, SOL_IP, IP_PKTINFO, sizeof(info), &info);
}
......@@ -992,20 +985,28 @@ e_inval:
}
/**
* ip_queue_rcv_skb - Queue an skb into sock receive queue
* ipv4_pktinfo_prepare - transfert some info from rtable to skb
* @sk: socket
* @skb: buffer
*
* Queues an skb into socket receive queue. If IP_CMSG_PKTINFO option
* is not set, we drop skb dst entry now, while dst cache line is hot.
* To support IP_CMSG_PKTINFO option, we store rt_iif and rt_spec_dst
* in skb->cb[] before dst drop.
* This way, receiver doesnt make cache line misses to read rtable.
*/
int ip_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
void ipv4_pktinfo_prepare(struct sk_buff *skb)
{
if (!(inet_sk(sk)->cmsg_flags & IP_CMSG_PKTINFO))
skb_dst_drop(skb);
return sock_queue_rcv_skb(sk, skb);
struct in_pktinfo *pktinfo = PKTINFO_SKB_CB(skb);
const struct rtable *rt = skb_rtable(skb);
if (rt) {
pktinfo->ipi_ifindex = rt->rt_iif;
pktinfo->ipi_spec_dst.s_addr = rt->rt_spec_dst;
} else {
pktinfo->ipi_ifindex = 0;
pktinfo->ipi_spec_dst.s_addr = 0;
}
skb_dst_drop(skb);
}
EXPORT_SYMBOL(ip_queue_rcv_skb);
int ip_setsockopt(struct sock *sk, int level,
int optname, char __user *optval, unsigned int optlen)
......
......@@ -292,7 +292,8 @@ static int raw_rcv_skb(struct sock * sk, struct sk_buff * skb)
{
/* Charge it to the socket. */
if (ip_queue_rcv_skb(sk, skb) < 0) {
ipv4_pktinfo_prepare(skb);
if (sock_queue_rcv_skb(sk, skb) < 0) {
kfree_skb(skb);
return NET_RX_DROP;
}
......
......@@ -1357,7 +1357,7 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
if (inet_sk(sk)->inet_daddr)
sock_rps_save_rxhash(sk, skb);
rc = ip_queue_rcv_skb(sk, skb);
rc = sock_queue_rcv_skb(sk, skb);
if (rc < 0) {
int is_udplite = IS_UDPLITE(sk);
......@@ -1473,6 +1473,7 @@ int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
rc = 0;
ipv4_pktinfo_prepare(skb);
bh_lock_sock(sk);
if (!sock_owned_by_user(sk))
rc = __udp_queue_rcv_skb(sk, skb);
......
......@@ -383,7 +383,8 @@ static inline int rawv6_rcv_skb(struct sock *sk, struct sk_buff *skb)
}
/* Charge it to the socket. */
if (ip_queue_rcv_skb(sk, skb) < 0) {
skb_dst_drop(skb);
if (sock_queue_rcv_skb(sk, skb) < 0) {
kfree_skb(skb);
return NET_RX_DROP;
}
......
......@@ -538,7 +538,9 @@ int udpv6_queue_rcv_skb(struct sock * sk, struct sk_buff *skb)
goto drop;
}
if ((rc = ip_queue_rcv_skb(sk, skb)) < 0) {
skb_dst_drop(skb);
rc = sock_queue_rcv_skb(sk, skb);
if (rc < 0) {
/* Note that an ENOMEM error is charged twice */
if (rc == -ENOMEM)
UDP6_INC_STATS_BH(sock_net(sk),
......
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