3 files changed, 38 insertions, 22 deletions

diff --git a/arch/ia64/kernel/time.c b/arch/ia64/kernel/time.c
index a094ec49ccfa..307d01e15b2e 100644
--- a/arch/ia64/kernel/time.c
+++ b/arch/ia64/kernel/time.c
@@ -250,32 +250,27 @@ time_init (void)
         set_normalized_timespec(&wall_to_monotonic, -xtime.tv_sec, -xtime.tv_nsec);
 }
 
-#define SMALLUSECS 100
-
-void
-udelay (unsigned long usecs)
+/*
+ * Generic udelay assumes that if preemption is allowed and the thread
+ * migrates to another CPU, that the ITC values are synchronized across
+ * all CPUs.
+ */
+static void
+ia64_itc_udelay (unsigned long usecs)
 {
-        unsigned long start;
-        unsigned long cycles;
-        unsigned long smallusecs;
+        unsigned long start = ia64_get_itc();
+        unsigned long end = start + usecs*local_cpu_data->cyc_per_usec;
 
-        /*
-         * Execute the non-preemptible delay loop (because the ITC might
-         * not be synchronized between CPUS) in relatively short time
-         * chunks, allowing preemption between the chunks.
-         */
-        while (usecs > 0) {
-                smallusecs = (usecs > SMALLUSECS) ? SMALLUSECS : usecs;
-                preempt_disable();
-                cycles = smallusecs*local_cpu_data->cyc_per_usec;
-                start = ia64_get_itc();
+        while (time_before(ia64_get_itc(), end))
+                cpu_relax();
+}
 
-                while (ia64_get_itc() - start < cycles)
-                        cpu_relax();
+void (*ia64_udelay)(unsigned long usecs) = &ia64_itc_udelay;
 
-                preempt_enable();
-                usecs -= smallusecs;
-        }
+void
+udelay (unsigned long usecs)
+{
+        (*ia64_udelay)(usecs);
 }
 EXPORT_SYMBOL(udelay);
 
diff --git a/arch/ia64/sn/kernel/sn2/timer.c b/arch/ia64/sn/kernel/sn2/timer.c
index deb9baf4d473..56a88b6df4b4 100644
--- a/arch/ia64/sn/kernel/sn2/timer.c
+++ b/arch/ia64/sn/kernel/sn2/timer.c
@@ -14,6 +14,7 @@
 
 #include <asm/hw_irq.h>
 #include <asm/system.h>
+#include <asm/timex.h>
 
 #include <asm/sn/leds.h>
 #include <asm/sn/shub_mmr.h>
@@ -28,9 +29,27 @@ static struct time_interpolator sn2_interpolator = {
         .source = TIME_SOURCE_MMIO64
 };
 
+/*
+ * sn udelay uses the RTC instead of the ITC because the ITC is not
+ * synchronized across all CPUs, and the thread may migrate to another CPU
+ * if preemption is enabled.
+ */
+static void
+ia64_sn_udelay (unsigned long usecs)
+{
+        unsigned long start = rtc_time();
+        unsigned long end = start +
+                        usecs * sn_rtc_cycles_per_second / 1000000;
+
+        while (time_before((unsigned long)rtc_time(), end))
+                cpu_relax();
+}
+
 void __init sn_timer_init(void)
 {
         sn2_interpolator.frequency = sn_rtc_cycles_per_second;
         sn2_interpolator.addr = RTC_COUNTER_ADDR;
         register_time_interpolator(&sn2_interpolator);
+
+        ia64_udelay = &ia64_sn_udelay;
 }
diff --git a/include/asm-ia64/timex.h b/include/asm-ia64/timex.h
index 414aae060440..05a6baf8a472 100644
--- a/include/asm-ia64/timex.h
+++ b/include/asm-ia64/timex.h
@@ -15,6 +15,8 @@
 
 typedef unsigned long cycles_t;
 
+extern void (*ia64_udelay)(unsigned long usecs);
+
 /*
  * For performance reasons, we don't want to define CLOCK_TICK_TRATE as
  * local_cpu_data->itc_rate.  Fortunately, we don't have to, either: according to George