kobject: factorize skb setup in kobject_uevent_net_broadcast()

We can build one skb and let it be cloned in netlink.

This is much faster, and use less memory (all clones will
share the same skb->head)

Tested:

time perf record (for f in `seq 1 3000` ; do ip netns add tast$f; done)
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 4.110 MB perf.data (~179584 samples) ]

real    0m24.227s # instead of 0m52.554s
user    0m0.329s
sys 0m23.753s # instead of 0m51.375s

    14.77%       ip  [kernel.kallsyms]  [k] __ip6addrlbl_add
    14.56%       ip  [kernel.kallsyms]  [k] netlink_broadcast_filtered
    11.65%       ip  [kernel.kallsyms]  [k] netlink_has_listeners
     6.19%       ip  [kernel.kallsyms]  [k] _raw_spin_lock_irqsave
     5.66%       ip  [kernel.kallsyms]  [k] kobject_uevent_env
     4.97%       ip  [kernel.kallsyms]  [k] memset_erms
     4.67%       ip  [kernel.kallsyms]  [k] refcount_sub_and_test
     4.41%       ip  [kernel.kallsyms]  [k] _raw_read_lock
     3.59%       ip  [kernel.kallsyms]  [k] refcount_inc_not_zero
     3.13%       ip  [kernel.kallsyms]  [k] _raw_spin_unlock_irqrestore
     1.55%       ip  [kernel.kallsyms]  [k] __wake_up
     1.20%       ip  [kernel.kallsyms]  [k] strlen
     1.03%       ip  [kernel.kallsyms]  [k] __wake_up_common
     0.93%       ip  [kernel.kallsyms]  [k] consume_skb
     0.92%       ip  [kernel.kallsyms]  [k] netlink_trim
     0.87%       ip  [kernel.kallsyms]  [k] insert_header
     0.63%       ip  [kernel.kallsyms]  [k] unmap_page_range

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index 78b2a7e..147db91 100644 (file)
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -301,23 +301,26 @@ static int kobject_uevent_net_broadcast(struct kobject *kobj,
 {
        int retval = 0;
 #if defined(CONFIG_NET)
+       struct sk_buff *skb = NULL;
        struct uevent_sock *ue_sk;
 
        /* send netlink message */
        list_for_each_entry(ue_sk, &uevent_sock_list, list) {
                struct sock *uevent_sock = ue_sk->sk;
-               struct sk_buff *skb;
-               size_t len;
 
                if (!netlink_has_listeners(uevent_sock, 1))
                        continue;
 
-               /* allocate message with the maximum possible size */
-               len = strlen(action_string) + strlen(devpath) + 2;
-               skb = alloc_skb(len + env->buflen, GFP_KERNEL);
-               if (skb) {
+               if (!skb) {
+                       /* allocate message with the maximum possible size */
+                       size_t len = strlen(action_string) + strlen(devpath) + 2;
                        char *scratch;
 
+                       retval = -ENOMEM;
+                       skb = alloc_skb(len + env->buflen, GFP_KERNEL);
+                       if (!skb)
+                               continue;
+
                        /* add header */
                        scratch = skb_put(skb, len);
                        sprintf(scratch, "%s@%s", action_string, devpath);
@@ -325,16 +328,17 @@ static int kobject_uevent_net_broadcast(struct kobject *kobj,
                        skb_put_data(skb, env->buf, env->buflen);
 
                        NETLINK_CB(skb).dst_group = 1;
-                       retval = netlink_broadcast_filtered(uevent_sock, skb,
-                                                           0, 1, GFP_KERNEL,
-                                                           kobj_bcast_filter,
-                                                           kobj);
-                       /* ENOBUFS should be handled in userspace */
-                       if (retval == -ENOBUFS || retval == -ESRCH)
-                               retval = 0;
-               } else
-                       retval = -ENOMEM;
+               }
+
+               retval = netlink_broadcast_filtered(uevent_sock, skb_get(skb),
+                                                   0, 1, GFP_KERNEL,
+                                                   kobj_bcast_filter,
+                                                   kobj);
+               /* ENOBUFS should be handled in userspace */
+               if (retval == -ENOBUFS || retval == -ESRCH)
+                       retval = 0;
        }
+       consume_skb(skb);
 #endif
        return retval;
 }