Commit 89c4b442 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

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: 217f6974 ("net: busy-poll: allow preemption in sk_busy_loop()")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1629dd4f

include/linux/netdevice.h

+0 −1
Original line number Diff line number Diff line
@@ -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;

include/linux/netpoll.h

+7 −6
Original line number Diff line number Diff line
@@ -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)

net/core/dev.c

+0 −1
Original line number Diff line number Diff line
@@ -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);

net/core/netpoll.c

+3 −3
Original line number Diff line number Diff line
@@ -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);

		}

	}

}

CRA Git | Maintained and supported by SUSTech CRA and CCSE