lk/linux-kernel-test
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

net: percpu net_device refcount

Browse Source 
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>
This commit is contained in:
Eric Dumazet
2010-10-11 10:22:12 +00:00
committed by David S. Miller
parent f0b9f47251
commit 29b4433d99
4 changed files with 41 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files

40
net/core/dev.c
View File

@ -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);