Re: [PATCH] Breaking down the global IPC locks - 2.5.31

[mingming cao <cmm@us.ibm.com>]

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mingming cao wrote:
> 
> This patch breaks the three global IPC locks into one lock per IPC ID.
> By doing so it could reduce possible lock contention in workloads which
> make heavy use of IPC semaphores, message queues and Shared
> memories...etc.

Here is the patch again. Fixed a typo. *_^

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diff -urN -X ../dontdiff ../base/linux-2.5.31/include/linux/ipc.h 2.5.31-ipc/include/linux/ipc.h
--- ../base/linux-2.5.31/include/linux/ipc.h	Sat Aug 10 18:41:16 2002
+++ 2.5.31-ipc/include/linux/ipc.h	Tue Aug 13 10:23:59 2002
@@ -56,6 +56,7 @@
 /* used by in-kernel data structures */
 struct kern_ipc_perm
 {
+	spinlock_t	lock;
 	key_t		key;
 	uid_t		uid;
 	gid_t		gid;
diff -urN -X ../dontdiff ../base/linux-2.5.31/ipc/util.c 2.5.31-ipc/ipc/util.c
--- ../base/linux-2.5.31/ipc/util.c	Sat Aug 10 18:41:27 2002
+++ 2.5.31-ipc/ipc/util.c	Wed Aug 14 15:59:19 2002
@@ -74,7 +74,7 @@
 		printk(KERN_ERR "ipc_init_ids() failed, ipc service disabled.\n");
 		ids->size = 0;
 	}
-	ids->ary = SPIN_LOCK_UNLOCKED;
+	ids->ary =RW_LOCK_UNLOCKED;
 	for(i=0;i<ids->size;i++)
 		ids->entries[i].p = NULL;
 }
@@ -120,13 +120,13 @@
 	for(i=ids->size;i<newsize;i++) {
 		new[i].p = NULL;
 	}
-	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 +165,9 @@
 	if(ids->seq > ids->seq_max)
 		ids->seq = 0;
 
-	spin_lock(&ids->ary);
+	new->lock = SPIN_LOCK_UNLOCKED;
+	read_lock(&ids->ary);
+	spin_lock(&new->lock);
 	ids->entries[id].p = new;
 	return id;
 }
diff -urN -X ../dontdiff ../base/linux-2.5.31/ipc/util.h 2.5.31-ipc/ipc/util.h
--- ../base/linux-2.5.31/ipc/util.h	Sat Aug 10 18:41:40 2002
+++ 2.5.31-ipc/ipc/util.h	Wed Aug 14 17:05:22 2002
@@ -19,7 +19,7 @@
 	unsigned short seq;
 	unsigned short seq_max;
 	struct semaphore sem;	
-	spinlock_t ary;
+	rwlock_t ary;
 	struct ipc_id* entries;
 };
 
@@ -47,7 +47,7 @@
 
 extern inline void ipc_lockall(struct ipc_ids* ids)
 {
-	spin_lock(&ids->ary);
+	write_lock(&ids->ary);
 }
 
 extern inline struct kern_ipc_perm* ipc_get(struct ipc_ids* ids, int id)
@@ -63,7 +63,7 @@
 
 extern inline void ipc_unlockall(struct ipc_ids* ids)
 {
-	spin_unlock(&ids->ary);
+	write_unlock(&ids->ary);
 }
 extern inline struct kern_ipc_perm* ipc_lock(struct ipc_ids* ids, int id)
 {
@@ -72,16 +72,29 @@
 	if(lid >= ids->size)
 		return NULL;
 
-	spin_lock(&ids->ary);
+	read_lock(&ids->ary);
 	out = ids->entries[lid].p;
-	if(out==NULL)
-		spin_unlock(&ids->ary);
+	if(out==NULL) {
+		read_unlock(&ids->ary);
+		return NULL;
+	}
+	spin_lock(&out->lock);
 	return out;
 }
 
 extern inline void ipc_unlock(struct ipc_ids* ids, int id)
 {
-	spin_unlock(&ids->ary);
+	int lid = id % SEQ_MULTIPLIER;
+	struct kern_ipc_perm* out;
+
+        if(lid >= ids->size)
+		return;
+	out = ids->entries[lid].p;
+	if (out == NULL)
+		return;
+
+	spin_unlock(&out->lock);
+	read_unlock(&ids->ary);
 }
 
 extern inline int ipc_buildid(struct ipc_ids* ids, int id, int seq)