[patch] Convert sockets_in_use to use per_cpu areas

[patch] Convert sockets_in_use to use per_cpu areas

[Ravikiran G Thirumalai]

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

[David S. Miller]

   From: Ravikiran G Thirumalai <kiran@in.ibm.com>
   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.

Re: [patch] Convert sockets_in_use to use per_cpu areas

[Chris Wedgwood]

On Mon, Dec 23, 2002 at 12:16:32PM -0800, David S. Miller wrote:

> 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.

I wonder if "some platforms with older GCC's" will ever have these
issues resolved...


  --cw

Re: [patch] Convert sockets_in_use to use per_cpu areas

[David S. Miller]

   From: Chris Wedgwood <cw@f00f.org>
   Date: Mon, 23 Dec 2002 16:00:48 -0800

   On Mon, Dec 23, 2002 at 12:16:32PM -0800, David S. Miller wrote:
   
   > 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.
   
   I wonder if "some platforms with older GCC's" will ever have these
   issues resolved...

I still don't have gcc-3.2.1 working properly on sparc64.

I hope to have it working soon, but this does mean that 2.6.x
cannot deprecate it, whereas 2.7.x certainly can.

Re: [patch] Convert sockets_in_use to use per_cpu areas

[Ravikiran G Thirumalai]

On Mon, Dec 23, 2002 at 12:16:32PM -0800, David S. Miller wrote:
>...     
>    -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.
> 

Ok, here's the modified patch...

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	Tue Dec 24 05:11:36 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) = 0;
 
 /*
  *	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

[David S. Miller]

   From: Ravikiran G Thirumalai <kiran@in.ibm.com>
   Date: Tue, 24 Dec 2002 12:18:52 +0530
   
   Ok, here's the modified patch...
   
Ok I'll apply this when I get back from vacation in the
new year.

Re: [patch] Convert sockets_in_use to use per_cpu areas

[David S. Miller]

Patch applied, thanks.