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: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -2701,7 +2701,7 @@ static int nes_disconnect(struct nes_qp *nesqp, int abrupt)
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nesibdev = nesvnic->nesibdev;
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nes_debug(NES_DBG_CM, "netdev refcnt = %u.\n",
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atomic_read(&nesvnic->netdev->refcnt));
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netdev_refcnt_read(nesvnic->netdev));
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if (nesqp->active_conn) {
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@ -2791,7 +2791,7 @@ int nes_accept(struct iw_cm_id *cm_id, struct iw_cm_conn_param *conn_param)
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atomic_inc(&cm_accepts);
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nes_debug(NES_DBG_CM, "netdev refcnt = %u.\n",
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atomic_read(&nesvnic->netdev->refcnt));
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netdev_refcnt_read(nesvnic->netdev));
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/* allocate the ietf frame and space for private data */
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nesqp->ietf_frame = pci_alloc_consistent(nesdev->pcidev,
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@ -785,7 +785,7 @@ static struct ib_pd *nes_alloc_pd(struct ib_device *ibdev,
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nes_debug(NES_DBG_PD, "nesvnic=%p, netdev=%p %s, ibdev=%p, context=%p, netdev refcnt=%u\n",
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nesvnic, nesdev->netdev[0], nesdev->netdev[0]->name, ibdev, context,
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atomic_read(&nesvnic->netdev->refcnt));
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netdev_refcnt_read(nesvnic->netdev));
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err = nes_alloc_resource(nesadapter, nesadapter->allocated_pds,
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nesadapter->max_pd, &pd_num, &nesadapter->next_pd);
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@ -1416,7 +1416,7 @@ static struct ib_qp *nes_create_qp(struct ib_pd *ibpd,
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/* update the QP table */
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nesdev->nesadapter->qp_table[nesqp->hwqp.qp_id-NES_FIRST_QPN] = nesqp;
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nes_debug(NES_DBG_QP, "netdev refcnt=%u\n",
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atomic_read(&nesvnic->netdev->refcnt));
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netdev_refcnt_read(nesvnic->netdev));
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return &nesqp->ibqp;
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}
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@ -1026,7 +1026,7 @@ struct net_device {
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struct timer_list watchdog_timer;
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/* Number of references to this device */
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atomic_t refcnt ____cacheline_aligned_in_smp;
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int __percpu *pcpu_refcnt;
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/* delayed register/unregister */
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struct list_head todo_list;
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@ -1330,6 +1330,7 @@ static inline void unregister_netdevice(struct net_device *dev)
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unregister_netdevice_queue(dev, NULL);
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}
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extern int netdev_refcnt_read(const struct net_device *dev);
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extern void free_netdev(struct net_device *dev);
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extern void synchronize_net(void);
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extern int register_netdevice_notifier(struct notifier_block *nb);
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@ -1798,7 +1799,7 @@ extern void netdev_run_todo(void);
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*/
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static inline void dev_put(struct net_device *dev)
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{
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atomic_dec(&dev->refcnt);
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irqsafe_cpu_dec(*dev->pcpu_refcnt);
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}
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/**
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@ -1809,7 +1810,7 @@ static inline void dev_put(struct net_device *dev)
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*/
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static inline void dev_hold(struct net_device *dev)
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{
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atomic_inc(&dev->refcnt);
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irqsafe_cpu_inc(*dev->pcpu_refcnt);
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}
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/* Carrier loss detection, dial on demand. The functions netif_carrier_on
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@ -5192,9 +5192,6 @@ int init_dummy_netdev(struct net_device *dev)
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*/
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dev->reg_state = NETREG_DUMMY;
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/* initialize the ref count */
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atomic_set(&dev->refcnt, 1);
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/* NAPI wants this */
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INIT_LIST_HEAD(&dev->napi_list);
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@ -5202,6 +5199,11 @@ int init_dummy_netdev(struct net_device *dev)
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set_bit(__LINK_STATE_PRESENT, &dev->state);
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set_bit(__LINK_STATE_START, &dev->state);
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/* Note : We dont allocate pcpu_refcnt for dummy devices,
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* because users of this 'device' dont need to change
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* its refcount.
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*/
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return 0;
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}
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EXPORT_SYMBOL_GPL(init_dummy_netdev);
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@ -5243,6 +5245,16 @@ out:
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}
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EXPORT_SYMBOL(register_netdev);
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int netdev_refcnt_read(const struct net_device *dev)
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{
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int i, refcnt = 0;
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for_each_possible_cpu(i)
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refcnt += *per_cpu_ptr(dev->pcpu_refcnt, i);
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return refcnt;
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}
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EXPORT_SYMBOL(netdev_refcnt_read);
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/*
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* netdev_wait_allrefs - wait until all references are gone.
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*
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@ -5257,11 +5269,14 @@ EXPORT_SYMBOL(register_netdev);
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static void netdev_wait_allrefs(struct net_device *dev)
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{
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unsigned long rebroadcast_time, warning_time;
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int refcnt;
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linkwatch_forget_dev(dev);
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rebroadcast_time = warning_time = jiffies;
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while (atomic_read(&dev->refcnt) != 0) {
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refcnt = netdev_refcnt_read(dev);
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while (refcnt != 0) {
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if (time_after(jiffies, rebroadcast_time + 1 * HZ)) {
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rtnl_lock();
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@ -5288,11 +5303,13 @@ static void netdev_wait_allrefs(struct net_device *dev)
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msleep(250);
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refcnt = netdev_refcnt_read(dev);
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if (time_after(jiffies, warning_time + 10 * HZ)) {
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printk(KERN_EMERG "unregister_netdevice: "
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"waiting for %s to become free. Usage "
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"count = %d\n",
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dev->name, atomic_read(&dev->refcnt));
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dev->name, refcnt);
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warning_time = jiffies;
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}
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}
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@ -5350,7 +5367,7 @@ void netdev_run_todo(void)
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netdev_wait_allrefs(dev);
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/* paranoia */
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BUG_ON(atomic_read(&dev->refcnt));
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BUG_ON(netdev_refcnt_read(dev));
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WARN_ON(rcu_dereference_raw(dev->ip_ptr));
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WARN_ON(dev->ip6_ptr);
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WARN_ON(dev->dn_ptr);
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@ -5520,9 +5537,13 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name,
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dev = PTR_ALIGN(p, NETDEV_ALIGN);
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dev->padded = (char *)dev - (char *)p;
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if (dev_addr_init(dev))
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dev->pcpu_refcnt = alloc_percpu(int);
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if (!dev->pcpu_refcnt)
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goto free_tx;
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if (dev_addr_init(dev))
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goto free_pcpu;
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dev_mc_init(dev);
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dev_uc_init(dev);
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@ -5553,6 +5574,8 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name,
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free_tx:
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kfree(tx);
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free_pcpu:
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free_percpu(dev->pcpu_refcnt);
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free_p:
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kfree(p);
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return NULL;
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@ -5586,6 +5609,9 @@ void free_netdev(struct net_device *dev)
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list_for_each_entry_safe(p, n, &dev->napi_list, dev_list)
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netif_napi_del(p);
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free_percpu(dev->pcpu_refcnt);
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dev->pcpu_refcnt = NULL;
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/* Compatibility with error handling in drivers */
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if (dev->reg_state == NETREG_UNINITIALIZED) {
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kfree((char *)dev - dev->padded);
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