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Message-ID: <1286825929.3218.7.camel@edumazet-laptop>
Date: Mon, 11 Oct 2010 21:38:49 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: percpu net_device refcount
Le lundi 11 octobre 2010 à 12:13 -0700, David Miller a écrit :
> Ok, I'm fine with this.
>
> But could you please get rid of that "#if 0" code block? The comment
> is fine and should stay, but the commented out code shouldn't really
> stay there.
Sure, here is second version, against latest net-next-2.6
Thanks !
[PATCH net-next] 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@...il.com>
---
include/linux/netdevice.h | 6 ++---
net/core/dev.c | 39 +++++++++++++++++++++++++++++-------
2 files changed, 35 insertions(+), 10 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4160db3..c0b5e05 100644
--- 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;
@@ -1798,7 +1798,7 @@ 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 +1809,7 @@ 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..4b2d820 100644
--- 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 +5245,15 @@ out:
}
EXPORT_SYMBOL(register_netdev);
+static 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;
+}
+
/*
* netdev_wait_allrefs - wait until all references are gone.
*
@@ -5257,11 +5268,14 @@ 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 +5302,13 @@ 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 +5366,7 @@ 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 +5536,13 @@ 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 +5573,8 @@ 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 +5608,9 @@ 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);
--
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