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net: use jump_label for netstamp_needed 

netstamp_needed seems a good candidate to jump_label conversion.

This avoids 3 conditional branches per incoming packet in fast path.

No measurable difference, given that these conditional branches are
predicted on modern cpus. Only a small icache reduction, thanks to the
unlikely() stuff.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2011-11-15 04:12:55 +00:00 committed by David S. Miller
parent 66846048f5
commit 588f033075
1 changed files with 14 additions and 18 deletions
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32
net/core/dev.c
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@ -137,6 +137,7 @@
#include <linux/if_pppox.h>
#include <linux/ppp_defs.h>
#include <linux/net_tstamp.h>
#include <linux/jump_label.h>
#include "net-sysfs.h"
@ -1449,34 +1450,32 @@ int call_netdevice_notifiers(unsigned long val, struct net_device *dev)
}
EXPORT_SYMBOL(call_netdevice_notifiers);
/* When > 0 there are consumers of rx skb time stamps */
static atomic_t netstamp_needed = ATOMIC_INIT(0);
static struct jump_label_key netstamp_needed __read_mostly;
void net_enable_timestamp(void)
{
atomic_inc(&netstamp_needed);
jump_label_inc(&netstamp_needed);
}
EXPORT_SYMBOL(net_enable_timestamp);
void net_disable_timestamp(void)
{
atomic_dec(&netstamp_needed);
jump_label_dec(&netstamp_needed);
}
EXPORT_SYMBOL(net_disable_timestamp);
static inline void net_timestamp_set(struct sk_buff *skb)
{
if (atomic_read(&netstamp_needed))
skb->tstamp.tv64 = 0;
if (static_branch(&netstamp_needed))
__net_timestamp(skb);
else
skb->tstamp.tv64 = 0;
}
static inline void net_timestamp_check(struct sk_buff *skb)
{
if (!skb->tstamp.tv64 && atomic_read(&netstamp_needed))
__net_timestamp(skb);
}
#define net_timestamp_check(COND, SKB) \
if (static_branch(&netstamp_needed)) { \
if ((COND) && !(SKB)->tstamp.tv64) \
__net_timestamp(SKB); \
} \
static int net_hwtstamp_validate(struct ifreq *ifr)
{
@ -2997,8 +2996,7 @@ int netif_rx(struct sk_buff *skb)
if (netpoll_rx(skb))
return NET_RX_DROP;
if (netdev_tstamp_prequeue)
net_timestamp_check(skb);
net_timestamp_check(netdev_tstamp_prequeue, skb);
trace_netif_rx(skb);
#ifdef CONFIG_RPS
@ -3230,8 +3228,7 @@ static int __netif_receive_skb(struct sk_buff *skb)
int ret = NET_RX_DROP;
__be16 type;
if (!netdev_tstamp_prequeue)
net_timestamp_check(skb);
net_timestamp_check(!netdev_tstamp_prequeue, skb);
trace_netif_receive_skb(skb);
@ -3362,8 +3359,7 @@ out:
*/
int netif_receive_skb(struct sk_buff *skb)
{
if (netdev_tstamp_prequeue)
net_timestamp_check(skb);
net_timestamp_check(netdev_tstamp_prequeue, skb);
if (skb_defer_rx_timestamp(skb))
return NET_RX_SUCCESS;