[Xen-devel] [PATCH]x86: add a range for hpet broadcast

["Wei, Gang" <gang.wei@xxxxxxxxx>]

x86: add a range for hpet broadcast

Apply a range timer like range to hpet broadcast, so that timer expires within
timer_slop ns across idle CPUs are capable to be aligned to reduce hpet intrs,
and save idle power.

Signed-off-by: Wei Gang <gang.wei@xxxxxxxxx>

diff -r 7f611de6b93c xen/arch/x86/hpet.c
--- a/xen/arch/x86/hpet.c       Tue Dec 08 14:14:27 2009 +0000
+++ b/xen/arch/x86/hpet.c       Wed Dec 09 16:13:29 2009 +0800
@@ -176,7 +176,7 @@ static void handle_hpet_broadcast(struct
 static void handle_hpet_broadcast(struct hpet_event_channel *ch)
 {
     cpumask_t mask;
-    s_time_t now, next_event;
+    s_time_t now, next_event, delay_event;
     int cpu;
 
     spin_lock_irq(&ch->lock);
@@ -195,6 +195,16 @@ again:
         else if ( per_cpu(timer_deadline, cpu) < next_event )
             next_event = per_cpu(timer_deadline, cpu);
     }
+
+    /* find the largest event in (next_event,next_event + timer_slop] */
+    delay_event = next_event;
+    for_each_cpu_mask(cpu, ch->cpumask)
+    {
+        if ( per_cpu(timer_deadline, cpu) > delay_event &&
+             per_cpu(timer_deadline, cpu) - timer_slop <= next_event )
+            delay_event = per_cpu(timer_deadline, cpu);
+    }
+    next_event = delay_event;
 
     /* wakeup the cpus which have an expired event. */
     evt_do_broadcast(mask);
@@ -649,7 +659,7 @@ void hpet_broadcast_enter(void)
     cpu_set(cpu, ch->cpumask);
 
     /* reprogram if current cpu expire time is nearer */
-    if ( this_cpu(timer_deadline) < ch->next_event )
+    if ( this_cpu(timer_deadline) + timer_slop < ch->next_event )
         reprogram_hpet_evt_channel(ch, this_cpu(timer_deadline), NOW(), 1);
 
     spin_unlock(&ch->lock);
diff -r 7f611de6b93c xen/common/timer.c
--- a/xen/common/timer.c        Tue Dec 08 14:14:27 2009 +0000
+++ b/xen/common/timer.c        Wed Dec 09 16:13:29 2009 +0800
@@ -25,7 +25,7 @@
  * We pull handlers off the timer list this far in future,
  * rather than reprogramming the time hardware.
  */
-static unsigned int timer_slop __read_mostly = 50000; /* 50 us */
+unsigned int timer_slop __read_mostly = 50000; /* 50 us */
 integer_param("timer_slop", timer_slop);
 
 struct timers {
diff -r 7f611de6b93c xen/include/xen/timer.h
--- a/xen/include/xen/timer.h   Tue Dec 08 14:14:27 2009 +0000
+++ b/xen/include/xen/timer.h   Wed Dec 09 16:13:29 2009 +0800
@@ -125,6 +125,9 @@ extern int reprogram_timer(s_time_t time
 /* calculate the aligned first tick time for a given periodic timer */ 
 extern s_time_t align_timer(s_time_t firsttick, uint64_t period);
 
+/* time slop for timer expiring */
+extern unsigned int timer_slop;
+
 #endif /* _TIMER_H_ */
 
 /*

Attachment: hpet-range.patch
Description: hpet-range.patch

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