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netpoll: more efficient locking 

Callers of netpoll_poll_lock() own NAPI_STATE_SCHED

Callers of netpoll_poll_unlock() have BH blocked between
the NAPI_STATE_SCHED being cleared and poll_lock is released.

We can avoid the spinlock which has no contention, and use cmpxchg()
on poll_owner which we need to set anyway.

This removes a possible lockdep violation after the cited commit,
since sk_busy_loop() re-enables BH before calling busy_poll_stop()

Fixes: 217f697436 ("net: busy-poll: allow preemption in sk_busy_loop()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2016-11-16 14:54:50 -08:00 committed by David S. Miller
parent 1629dd4f76
commit 89c4b442b7
4 changed files with 10 additions and 11 deletions
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1
include/linux/netdevice.h
View File

@ -316,7 +316,6 @@ struct napi_struct {
unsigned int gro_count;
int (*poll)(struct napi_struct *, int);
#ifdef CONFIG_NETPOLL
spinlock_t poll_lock;
int poll_owner;
#endif
struct net_device *dev;

13
include/linux/netpoll.h
View File

@ -78,8 +78,11 @@ static inline void *netpoll_poll_lock(struct napi_struct *napi)
struct net_device *dev = napi->dev;
if (dev && dev->npinfo) {
spin_lock(&napi->poll_lock);
napi->poll_owner = smp_processor_id();
int owner = smp_processor_id();
while (cmpxchg(&napi->poll_owner, -1, owner) != -1)
cpu_relax();
return napi;
}
return NULL;
@ -89,10 +92,8 @@ static inline void netpoll_poll_unlock(void *have)
{
struct napi_struct *napi = have;
if (napi) {
napi->poll_owner = -1;
spin_unlock(&napi->poll_lock);
}
if (napi)
smp_store_release(&napi->poll_owner, -1);
}
static inline bool netpoll_tx_running(struct net_device *dev)

1
net/core/dev.c
View File

@ -5143,7 +5143,6 @@ void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
list_add(&napi->dev_list, &dev->napi_list);
napi->dev = dev;
#ifdef CONFIG_NETPOLL
spin_lock_init(&napi->poll_lock);
napi->poll_owner = -1;
#endif
set_bit(NAPI_STATE_SCHED, &napi->state);

6
net/core/netpoll.c
View File

@ -171,12 +171,12 @@ static void poll_one_napi(struct napi_struct *napi)
static void poll_napi(struct net_device *dev)
{
struct napi_struct *napi;
int cpu = smp_processor_id();
list_for_each_entry(napi, &dev->napi_list, dev_list) {
if (napi->poll_owner != smp_processor_id() &&
spin_trylock(&napi->poll_lock)) {
if (cmpxchg(&napi->poll_owner, -1, cpu) == -1) {
poll_one_napi(napi);
spin_unlock(&napi->poll_lock);
smp_store_release(&napi->poll_owner, -1);
}
}
}