[patch] Convert sockets_in_use to use per_cpu areas

[Ravikiran G Thirumalai <kiran@xxxxxxxxxx>]

Hi,
Here's a simple patch to change sockets_in_use to make use of 
per-cpu areas.  

I have couple of questions though... 
1. Was this var made per-cpu just to avoid  atomic_t or locking 
   or are there real life workloads which cause too many sock_alloc
   and sock_releases to cause cacheline bouncing?
2. Is this var required? since we can just sum up all proto->stats.inuse 
   and remove this var altogether? (This var is read only for /proc 
   reporting)

Thanks,
Kiran


diff -ruN -X dontdiff linux-2.5.52/net/socket.c 
sockets_in_use-2.5.52/net/socket.c
--- linux-2.5.52/net/socket.c   Mon Dec 16 07:37:53 2002
+++ sockets_in_use-2.5.52/net/socket.c  Mon Dec 23 11:48:44 2002
@@ -189,10 +189,7 @@
  *     Statistics counters of the socket lists
  */
 
-static union {
-       int     counter;
-       char    __pad[SMP_CACHE_BYTES];
-} sockets_in_use[NR_CPUS] __cacheline_aligned = {{0}};
+static DEFINE_PER_CPU(int, sockets_in_use);
 
 /*
  *     Support routines. Move socket addresses back and forth across the 
kernel/user
@@ -475,7 +472,8 @@
        inode->i_uid = current->fsuid;
        inode->i_gid = current->fsgid;
 
-       sockets_in_use[smp_processor_id()].counter++;
+       get_cpu_var(sockets_in_use)++;
+       put_cpu_var(sockets_in_use);
        return sock;
 }
 
@@ -511,7 +509,8 @@
        if (sock->fasync_list)
                printk(KERN_ERR "sock_release: fasync list not empty!\n");
 
-       sockets_in_use[smp_processor_id()].counter--;
+       get_cpu_var(sockets_in_use)--;
+       put_cpu_var(sockets_in_use);
        if (!sock->file) {
                iput(SOCK_INODE(sock));
                return;
@@ -1851,7 +1850,7 @@
        int counter = 0;
 
        for (cpu = 0; cpu < NR_CPUS; cpu++)
-               counter += sockets_in_use[cpu].counter;
+               counter += per_cpu(sockets_in_use, cpu);
 
        /* It can be negative, by the way. 8) */
        if (counter < 0)