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>

diff --git a/drivers/infiniband/hw/nes/nes_cm.c b/drivers/infiniband/hw/nes/nes_cm.c
index 61e0efd..6220d9d 100644 (file)
--- a/drivers/infiniband/hw/nes/nes_cm.c
+++ b/drivers/infiniband/hw/nes/nes_cm.c
@@ -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,

diff --git a/drivers/infiniband/hw/nes/nes_verbs.c b/drivers/infiniband/hw/nes/nes_verbs.c
index 9046e66..546fc22 100644 (file)
--- a/drivers/infiniband/hw/nes/nes_verbs.c
+++ b/drivers/infiniband/hw/nes/nes_verbs.c
@@ -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;
 }

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4160db3..14fbb04 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -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

diff --git a/net/core/dev.c b/net/core/dev.c
index 193eafa..04972a4 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -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 @@ out:
 }
 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);