[PATCH] (3/4) 2.5.59 fast reader/writer lock for gettimeofday

[Stephen Hemminger]

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This is the ia64 portion of lockless gettimeofday. It defines frlock
and changes locking of xtime_lock from rwlock to frlock.

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diff -urN -X dontdiff linux-2.5.59/arch/ia64/kernel/time.c linux-2.5-frlock/arch/ia64/kernel/time.c
--- linux-2.5.59/arch/ia64/kernel/time.c	2003-01-17 09:42:15.000000000 -0800
+++ linux-2.5-frlock/arch/ia64/kernel/time.c	2003-01-24 14:54:11.000000000 -0800
@@ -24,7 +24,7 @@
 #include <asm/sal.h>
 #include <asm/system.h>
 
-extern rwlock_t xtime_lock;
+extern frlock_t xtime_lock;
 extern unsigned long wall_jiffies;
 extern unsigned long last_time_offset;
 
@@ -89,7 +89,7 @@
 void
 do_settimeofday (struct timeval *tv)
 {
-	write_lock_irq(&xtime_lock);
+	fr_write_lock_irq(&xtime_lock);
 	{
 		/*
 		 * This is revolting. We need to set "xtime" correctly. However, the value
@@ -112,21 +112,21 @@
 		time_maxerror = NTP_PHASE_LIMIT;
 		time_esterror = NTP_PHASE_LIMIT;
 	}
-	write_unlock_irq(&xtime_lock);
+	fr_write_unlock_irq(&xtime_lock);
 }
 
 void
 do_gettimeofday (struct timeval *tv)
 {
-	unsigned long flags, usec, sec, old;
+	unsigned long seq, usec, sec, old;
 
-	read_lock_irqsave(&xtime_lock, flags);
-	{
+	do {
+		seq = fr_read_begin(&xtime_lock);
 		usec = gettimeoffset();
 
 		/*
-		 * Ensure time never goes backwards, even when ITC on different CPUs are
-		 * not perfectly synchronized.
+		 * Ensure time never goes backwards, even when ITC on 
+		 * different CPUs are not perfectly synchronized.
 		 */
 		do {
 			old = last_time_offset;
@@ -138,8 +138,8 @@
 
 		sec = xtime.tv_sec;
 		usec += xtime.tv_nsec / 1000;
-	}
-	read_unlock_irqrestore(&xtime_lock, flags);
+	} while (seq != fr_read_end(&xtime_lock));
+
 
 	while (usec >= 1000000) {
 		usec -= 1000000;
@@ -182,10 +182,10 @@
 			 * another CPU. We need to avoid to SMP race by acquiring the
 			 * xtime_lock.
 			 */
-			write_lock(&xtime_lock);
+			fr_write_lock(&xtime_lock);
 			do_timer(regs);
 			local_cpu_data->itm_next = new_itm;
-			write_unlock(&xtime_lock);
+			fr_write_unlock(&xtime_lock);
 		} else
 			local_cpu_data->itm_next = new_itm;
 

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