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Commit 29b4433d authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net: percpu net_device refcount 



We tried very hard to remove all possible dev_hold()/dev_put() pairs in
network stack, using RCU conversions.

There is still an unavoidable device refcount change for every dst we
create/destroy, and this can slow down some workloads (routers or some
app servers, mmap af_packet)

We can switch to a percpu refcount implementation, now dynamic per_cpu
infrastructure is mature. On a 64 cpus machine, this consumes 256 bytes
per device.

On x86, dev_hold(dev) code :

before
        lock    incl 0x280(%ebx)
after:
        movl    0x260(%ebx),%eax
        incl    fs:(%eax)

Stress bench :

(Sending 160.000.000 UDP frames,
IP route cache disabled, dual E5540 @2.53GHz,
32bit kernel, FIB_TRIE)

Before:

real    1m1.662s
user    0m14.373s
sys     12m55.960s

After:

real    0m51.179s
user    0m15.329s
sys     10m15.942s

Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f0b9f472

drivers/infiniband/hw/nes/nes_cm.c

+2 −2
Original line number Diff line number Diff line
@@ -2701,7 +2701,7 @@ static int nes_disconnect(struct nes_qp *nesqp, int abrupt) 
	nesibdev = nesvnic->nesibdev;



	nes_debug(NES_DBG_CM, "netdev refcnt = %u.\n",

			atomic_read(&nesvnic->netdev->refcnt));

			netdev_refcnt_read(nesvnic->netdev));



	if (nesqp->active_conn) {
@@ -2791,7 +2791,7 @@ int nes_accept(struct iw_cm_id *cm_id, struct iw_cm_conn_param *conn_param) 
	atomic_inc(&cm_accepts);



	nes_debug(NES_DBG_CM, "netdev refcnt = %u.\n",

			atomic_read(&nesvnic->netdev->refcnt));

			netdev_refcnt_read(nesvnic->netdev));



	/* allocate the ietf frame and space for private data */

	nesqp->ietf_frame = pci_alloc_consistent(nesdev->pcidev,

drivers/infiniband/hw/nes/nes_verbs.c

+2 −2
Original line number Diff line number Diff line
@@ -785,7 +785,7 @@ static struct ib_pd *nes_alloc_pd(struct ib_device *ibdev, 


	nes_debug(NES_DBG_PD, "nesvnic=%p, netdev=%p %s, ibdev=%p, context=%p, netdev refcnt=%u\n",

			nesvnic, nesdev->netdev[0], nesdev->netdev[0]->name, ibdev, context,

			atomic_read(&nesvnic->netdev->refcnt));

			netdev_refcnt_read(nesvnic->netdev));



	err = nes_alloc_resource(nesadapter, nesadapter->allocated_pds,

			nesadapter->max_pd, &pd_num, &nesadapter->next_pd);
@@ -1416,7 +1416,7 @@ static struct ib_qp *nes_create_qp(struct ib_pd *ibpd, 
	/* update the QP table */

	nesdev->nesadapter->qp_table[nesqp->hwqp.qp_id-NES_FIRST_QPN] = nesqp;

	nes_debug(NES_DBG_QP, "netdev refcnt=%u\n",

			atomic_read(&nesvnic->netdev->refcnt));

			netdev_refcnt_read(nesvnic->netdev));



	return &nesqp->ibqp;

}

include/linux/netdevice.h

+4 −3
Original line number Diff line number Diff line
@@ -1026,7 +1026,7 @@ struct net_device { 
	struct timer_list	watchdog_timer;



	/* Number of references to this device */

	atomic_t		refcnt ____cacheline_aligned_in_smp;

	int __percpu		*pcpu_refcnt;



	/* delayed register/unregister */

	struct list_head	todo_list;
@@ -1330,6 +1330,7 @@ static inline void unregister_netdevice(struct net_device *dev) 
	unregister_netdevice_queue(dev, NULL);

}



extern int 		netdev_refcnt_read(const struct net_device *dev);

extern void		free_netdev(struct net_device *dev);

extern void		synchronize_net(void);

extern int 		register_netdevice_notifier(struct notifier_block *nb);
@@ -1798,7 +1799,7 @@ extern void netdev_run_todo(void); 
 */

static inline void dev_put(struct net_device *dev)

{

	atomic_dec(&dev->refcnt);

	irqsafe_cpu_dec(*dev->pcpu_refcnt);

}



/**
@@ -1809,7 +1810,7 @@ static inline void dev_put(struct net_device *dev) 
 */

static inline void dev_hold(struct net_device *dev)

{

	atomic_inc(&dev->refcnt);

	irqsafe_cpu_inc(*dev->pcpu_refcnt);

}



/* Carrier loss detection, dial on demand. The functions netif_carrier_on

net/core/dev.c

+33 −7
Original line number Diff line number Diff line
@@ -5192,9 +5192,6 @@ int init_dummy_netdev(struct net_device *dev) 
	 */

	dev->reg_state = NETREG_DUMMY;



	/* initialize the ref count */

	atomic_set(&dev->refcnt, 1);



	/* NAPI wants this */

	INIT_LIST_HEAD(&dev->napi_list);
@@ -5202,6 +5199,11 @@ int init_dummy_netdev(struct net_device *dev) 
	set_bit(__LINK_STATE_PRESENT, &dev->state);

	set_bit(__LINK_STATE_START, &dev->state);



	/* Note : We dont allocate pcpu_refcnt for dummy devices,

	 * because users of this 'device' dont need to change

	 * its refcount.

	 */



	return 0;

}

EXPORT_SYMBOL_GPL(init_dummy_netdev);
@@ -5243,6 +5245,16 @@ int register_netdev(struct net_device *dev) 
}

EXPORT_SYMBOL(register_netdev);



int netdev_refcnt_read(const struct net_device *dev)

{

	int i, refcnt = 0;



	for_each_possible_cpu(i)

		refcnt += *per_cpu_ptr(dev->pcpu_refcnt, i);

	return refcnt;

}

EXPORT_SYMBOL(netdev_refcnt_read);



/*

 * netdev_wait_allrefs - wait until all references are gone.

 *
@@ -5257,11 +5269,14 @@ EXPORT_SYMBOL(register_netdev); 
static void netdev_wait_allrefs(struct net_device *dev)

{

	unsigned long rebroadcast_time, warning_time;

	int refcnt;



	linkwatch_forget_dev(dev);



	rebroadcast_time = warning_time = jiffies;

	while (atomic_read(&dev->refcnt) != 0) {

	refcnt = netdev_refcnt_read(dev);



	while (refcnt != 0) {

		if (time_after(jiffies, rebroadcast_time + 1 * HZ)) {

			rtnl_lock();
@@ -5288,11 +5303,13 @@ static void netdev_wait_allrefs(struct net_device *dev) 


		msleep(250);



		refcnt = netdev_refcnt_read(dev);



		if (time_after(jiffies, warning_time + 10 * HZ)) {

			printk(KERN_EMERG "unregister_netdevice: "

			       "waiting for %s to become free. Usage "

			       "count = %d\n",

			       dev->name, atomic_read(&dev->refcnt));

			       dev->name, refcnt);

			warning_time = jiffies;

		}

	}
@@ -5350,7 +5367,7 @@ void netdev_run_todo(void) 
		netdev_wait_allrefs(dev);



		/* paranoia */

		BUG_ON(atomic_read(&dev->refcnt));

		BUG_ON(netdev_refcnt_read(dev));

		WARN_ON(rcu_dereference_raw(dev->ip_ptr));

		WARN_ON(dev->ip6_ptr);

		WARN_ON(dev->dn_ptr);
@@ -5520,9 +5537,13 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name, 
	dev = PTR_ALIGN(p, NETDEV_ALIGN);

	dev->padded = (char *)dev - (char *)p;



	if (dev_addr_init(dev))

	dev->pcpu_refcnt = alloc_percpu(int);

	if (!dev->pcpu_refcnt)

		goto free_tx;



	if (dev_addr_init(dev))

		goto free_pcpu;



	dev_mc_init(dev);

	dev_uc_init(dev);
@@ -5553,6 +5574,8 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name, 


free_tx:

	kfree(tx);

free_pcpu:

	free_percpu(dev->pcpu_refcnt);

free_p:

	kfree(p);

	return NULL;
@@ -5586,6 +5609,9 @@ void free_netdev(struct net_device *dev) 
	list_for_each_entry_safe(p, n, &dev->napi_list, dev_list)

		netif_napi_del(p);



	free_percpu(dev->pcpu_refcnt);

	dev->pcpu_refcnt = NULL;



	/*  Compatibility with error handling in drivers */

	if (dev->reg_state == NETREG_UNINITIALIZED) {

		kfree((char *)dev - dev->padded);