[Xen-devel] [PATCH] CPUIDLE: shorten hpet spin_lock holding time

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

CPUIDLE: shorten hpet spin_lock holding time

Try to reduce spin_lock overhead for deep C state entry/exit. This will benefit 
systems with a lot of cpus which need the hpet broadcast to wakeup from deep C 
state.

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

diff -r 7ee8bb40200a xen/arch/x86/hpet.c
--- a/xen/arch/x86/hpet.c       Thu Apr 15 19:11:16 2010 +0100
+++ b/xen/arch/x86/hpet.c       Fri Apr 16 15:05:28 2010 +0800
@@ -186,6 +186,9 @@ static void handle_hpet_broadcast(struct
 
 again:
     ch->next_event = STIME_MAX;
+
+    spin_unlock_irq(&ch->lock);
+
     next_event = STIME_MAX;
     mask = (cpumask_t)CPU_MASK_NONE;
     now = NOW();
@@ -204,10 +207,14 @@ again:
 
     if ( next_event != STIME_MAX )
     {
-        if ( reprogram_hpet_evt_channel(ch, next_event, now, 0) )
+        spin_lock_irq(&ch->lock);
+
+        if ( next_event < ch->next_event &&
+             reprogram_hpet_evt_channel(ch, next_event, now, 0) )
             goto again;
-    }
-    spin_unlock_irq(&ch->lock);
+
+        spin_unlock_irq(&ch->lock);
+    }
 }
 
 static void hpet_interrupt_handler(int irq, void *data,
@@ -656,10 +663,15 @@ void hpet_broadcast_enter(void)
     BUG_ON( !ch );
 
     ASSERT(!local_irq_is_enabled());
-    spin_lock(&ch->lock);
 
     if ( hpet_attach_channel )
+    {
+        spin_lock(&ch->lock);
+
         hpet_attach_channel(cpu, ch);
+
+        spin_unlock(&ch->lock);
+    }
 
     /* Cancel any outstanding LAPIC timer event and disable interrupts. */
     reprogram_timer(0);
@@ -667,6 +679,8 @@ void hpet_broadcast_enter(void)
 
     cpu_set(cpu, ch->cpumask);
 
+    spin_lock(&ch->lock);
+
     /* reprogram if current cpu expire time is nearer */
     if ( this_cpu(timer_deadline_end) < ch->next_event )
         reprogram_hpet_evt_channel(ch, this_cpu(timer_deadline_end), NOW(), 1);
@@ -683,8 +697,6 @@ void hpet_broadcast_exit(void)
         return;
 
     BUG_ON( !ch );
-
-    spin_lock_irq(&ch->lock);
 
     if ( cpu_test_and_clear(cpu, ch->cpumask) )
     {
@@ -693,14 +705,22 @@ void hpet_broadcast_exit(void)
         if ( !reprogram_timer(this_cpu(timer_deadline_start)) )
             raise_softirq(TIMER_SOFTIRQ);
 
+        spin_lock_irq(&ch->lock);
+
         if ( cpus_empty(ch->cpumask) && ch->next_event != STIME_MAX )
             reprogram_hpet_evt_channel(ch, STIME_MAX, 0, 0);
+
+        spin_unlock_irq(&ch->lock);
     }
 
     if ( hpet_detach_channel )
+    {
+        spin_lock_irq(&ch->lock);
+
         hpet_detach_channel(cpu);
 
-    spin_unlock_irq(&ch->lock);
+        spin_unlock_irq(&ch->lock);
+    }
 }
 
 int hpet_broadcast_is_available(void)

Attachment: hpet_short_lock.patch
Description: hpet_short_lock.patch

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