Break the global IPC locks

Currently the use of three type of IPC resources(semaphores, message
queues and shared memory segments) are synchronized by three global
locks respectively.  This means, for example, all semaphores are going
to share one global lock.  Although the IPC locks are not highly used as
the BKL, on some applications which use lots of IPC resources(e.g. IPC
semaphores), there could be contention.

It makes more sense to me if we break the one globale lock for all
semaphores into one lock per sempahore id(same for message queue
id/shared memory id).  I attached a patch which implements this idea. 
Just sharing my thoughts with you.  Please send any of your comments to
me.

Patch applies against 2.5.25, also for 2.4.18.
-- 
Mingming Cao
IBM Linux Technology Centerdiff -urN -X ../dontdiff ../base/linux-2.4.17/ipc/util.c ipc/ipc/util.c
--- ../base/linux-2.4.17/ipc/util.c	Sun Aug 12 17:37:53 2001
+++ ipc/ipc/util.c	Mon May  6 15:11:21 2002
@@ -74,9 +74,11 @@
 		printk(KERN_ERR "ipc_init_ids() failed, ipc service disabled.\n");
 		ids->size = 0;
 	}
-	ids->ary = SPIN_LOCK_UNLOCKED;
-	for(i=0;i<ids->size;i++)
+	ids->ary =RW_LOCK_UNLOCKED;
+	for(i=0;i<ids->size;i++) {
 		ids->entries[i].p = NULL;
+		ids->entries[i].lock = SPIN_LOCK_UNLOCKED;
+	}
 }
 
 /**
@@ -119,14 +121,15 @@
 	memcpy(new, ids->entries, sizeof(struct ipc_id)*ids->size);
 	for(i=ids->size;i<newsize;i++) {
 		new[i].p = NULL;
+		new[i].lock = SPIN_LOCK_UNLOCKED;
 	}
-	spin_lock(&ids->ary);
+	write_lock(&ids->ary);
 
 	old = ids->entries;
 	ids->entries = new;
 	i = ids->size;
 	ids->size = newsize;
-	spin_unlock(&ids->ary);
+	write_unlock(&ids->ary);
 	ipc_free(old, sizeof(struct ipc_id)*i);
 	return ids->size;
 }
@@ -165,7 +168,8 @@
 	if(ids->seq > ids->seq_max)
 		ids->seq = 0;
 
-	spin_lock(&ids->ary);
+	read_lock(&ids->ary);
+	spin_lock(&ids->entries[id].lock);
 	ids->entries[id].p = new;
 	return id;
 }
diff -urN -X ../dontdiff ../base/linux-2.4.17/ipc/util.h ipc/ipc/util.h
--- ../base/linux-2.4.17/ipc/util.h	Mon Feb 19 10:18:18 2001
+++ ipc/ipc/util.h	Mon May  6 15:14:39 2002
@@ -19,12 +19,13 @@
 	unsigned short seq;
 	unsigned short seq_max;
 	struct semaphore sem;	
-	spinlock_t ary;
+	rwlock_t ary;
 	struct ipc_id* entries;
 };
 
 struct ipc_id {
 	struct kern_ipc_perm* p;
+	spinlock_t	lock;
 };
 
 
@@ -47,7 +48,7 @@
 
 extern inline void ipc_lockall(struct ipc_ids* ids)
 {
-	spin_lock(&ids->ary);
+	read_lock(&ids->ary);
 }
 
 extern inline struct kern_ipc_perm* ipc_get(struct ipc_ids* ids, int id)
@@ -63,7 +64,7 @@
 
 extern inline void ipc_unlockall(struct ipc_ids* ids)
 {
-	spin_unlock(&ids->ary);
+	read_unlock(&ids->ary);
 }
 extern inline struct kern_ipc_perm* ipc_lock(struct ipc_ids* ids, int id)
 {
@@ -72,16 +73,22 @@
 	if(lid >= ids->size)
 		return NULL;
 
-	spin_lock(&ids->ary);
+	read_lock(&ids->ary);
+	spin_lock(&ids->entries[lid].lock);
 	out = ids->entries[lid].p;
-	if(out==NULL)
-		spin_unlock(&ids->ary);
+	if(out==NULL) {
+		spin_unlock(&ids->entries[lid].lock);
+		read_unlock(&ids->ary);
+	}
 	return out;
 }
 
 extern inline void ipc_unlock(struct ipc_ids* ids, int id)
 {
-	spin_unlock(&ids->ary);
+	int lid = id % SEQ_MULTIPLIER;
+        if(lid < ids->size)
+		spin_unlock(&ids->entries[lid].lock);
+	read_unlock(&ids->ary);
 }
 
 extern inline int ipc_buildid(struct ipc_ids* ids, int id, int seq)