[PATCH] Read-Copy Update infrastructure

This is the RCU core patch from akpm's tree. It has been in his
tree since about 2.5.37-mm1 along with dcache_rcu and so far it has
worked fine. For 2.5, I am hoping that we might get the following
RCU patches included -

1. rt_rcu - ipv4 routecache lookup. Davem agreed to include this patch
   if and when you include RCU core in your tree.

2. dcache_rcu (by Maneesh Soni) - dcache lookup avoiding dcache_lock as
   much as possible. This has been akpm's tree - stable and gives us
   good yield. I have been submitting this to Viro and I will publish
   some more benchmark numbers later to help decide on this.

This RCU core implements RCU APIs, call_rcu() and synchronize_kernel(),
by monitoring a per-CPU quiescent state (idle/user etc.) counter.
call_rcu() queues a callback to be invoked after all the CPUs have
gone through a quiescent state. Queuing is per-CPU and each per-CPU
batch gets a batch number. As batches get their turn, a global
cpu mask is used to keep track of CPUs pending quiescent state.
Checking for quiescent cycle is done by saving the per-CPU
counter at the beginning of the batch and then monitoring it for change
through the local timer interrupt handler.

1 files changed, 134 insertions, 0 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
new file mode 100644
index 000000000000..a5ffb7bb5743
--- /dev/null
+++ b/include/linux/rcupdate.h
@@ -0,0 +1,134 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion 
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (c) IBM Corporation, 2001
+ *
+ * Author: Dipankar Sarma <dipankar@in.ibm.com>
+ * 
+ * Based on the original work by Paul McKenney <paul.mckenney@us.ibm.com>
+ * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
+ * Papers:
+ * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
+ * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * 		http://lse.sourceforge.net/locking/rcupdate.html
+ *
+ */
+
+#ifndef __LINUX_RCUPDATE_H
+#define __LINUX_RCUPDATE_H
+
+#ifdef __KERNEL__
+
+#include <linux/cache.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/threads.h>
+
+/**
+ * struct rcu_head - callback structure for use with RCU
+ * @list: list_head to queue the update requests
+ * @func: actual update function to call after the grace period.
+ * @arg: argument to be passed to the actual update function.
+ */
+struct rcu_head {
+	struct list_head list;
+	void (*func)(void *obj);
+	void *arg;
+};
+
+#define RCU_HEAD_INIT(head) \
+		{ list: LIST_HEAD_INIT(head.list), func: NULL, arg: NULL }
+#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT(head)
+#define INIT_RCU_HEAD(ptr) do { \
+       INIT_LIST_HEAD(&(ptr)->list); (ptr)->func = NULL; (ptr)->arg = NULL; \
+} while (0)
+
+
+
+/* Control variables for rcupdate callback mechanism. */
+struct rcu_ctrlblk {
+	spinlock_t	mutex;		/* Guard this struct                  */
+	long		curbatch;	/* Current batch number.	      */
+	long		maxbatch;	/* Max requested batch number.        */
+	unsigned long	rcu_cpu_mask; 	/* CPUs that need to switch in order  */
+					/* for current batch to proceed.      */
+};
+
+/* Is batch a before batch b ? */
+static inline int rcu_batch_before(long a, long b)
+{
+        return (a - b) < 0;
+}
+
+/* Is batch a after batch b ? */
+static inline int rcu_batch_after(long a, long b)
+{
+        return (a - b) > 0;
+}
+
+/*
+ * Per-CPU data for Read-Copy UPdate.
+ * nxtlist - new callbacks are added here
+ * curlist - current batch for which quiescent cycle started if any
+ */
+struct rcu_data {
+	long		qsctr;		 /* User-mode/idle loop etc. */
+        long            last_qsctr;	 /* value of qsctr at beginning */
+                                         /* of rcu grace period */
+        long  	       	batch;           /* Batch # for current RCU batch */
+        struct list_head  nxtlist;
+        struct list_head  curlist;
+} ____cacheline_aligned_in_smp;
+
+extern struct rcu_data rcu_data[NR_CPUS];
+extern struct rcu_ctrlblk rcu_ctrlblk;
+
+#define RCU_qsctr(cpu) 		(rcu_data[(cpu)].qsctr)
+#define RCU_last_qsctr(cpu) 	(rcu_data[(cpu)].last_qsctr)
+#define RCU_batch(cpu) 		(rcu_data[(cpu)].batch)
+#define RCU_nxtlist(cpu) 	(rcu_data[(cpu)].nxtlist)
+#define RCU_curlist(cpu) 	(rcu_data[(cpu)].curlist)
+
+#define RCU_QSCTR_INVALID	0
+
+static inline int rcu_pending(int cpu) 
+{
+	if ((!list_empty(&RCU_curlist(cpu)) &&
+	     rcu_batch_before(RCU_batch(cpu), rcu_ctrlblk.curbatch)) ||
+	    (list_empty(&RCU_curlist(cpu)) &&
+			 !list_empty(&RCU_nxtlist(cpu))) ||
+	    test_bit(cpu, &rcu_ctrlblk.rcu_cpu_mask))
+		return 1;
+	else
+		return 0;
+}
+
+#define rcu_read_lock()		preempt_disable()
+#define rcu_read_unlock()	preempt_enable()
+
+extern void rcu_init(void);
+extern void rcu_check_callbacks(int cpu, int user);
+
+/* Exported interfaces */
+extern void FASTCALL(call_rcu(struct rcu_head *head, 
+                          void (*func)(void *arg), void *arg));
+extern void synchronize_kernel(void);
+
+#endif /* __KERNEL__ */
+#endif /* __LINUX_RCUPDATE_H */