[patch] Convert sockets_in_use to use per_cpu areas

From: Ravikiran G Thirumalai <hidden>
Date: 2002-12-23 13:33:49

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)

Re: [patch] Convert sockets_in_use to use per_cpu areas

From: David S. Miller <hidden>
Date: 2002-12-23 20:14:19

   From: Ravikiran G Thirumalai [off-list ref]
   Date: Mon, 23 Dec 2002 19:08:48 +0530

   -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);

You have to provide an explicit initializer for DEFINE_PER_CPU
declarations or you break some platforms with older GCC's which
otherwise won't put it into the proper section.

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