Xen devel - Jun 2010 - [PATCH6/6] cpuidle: redefine cpumask_lock as rwlock_t

cpuidle: redefine cpumask_lock as rwlock_t

Multiple cpus clear hpet channel cpumask simultaneously is ok. So we can change
the cpumask_lock to rwlock_t.

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

diff -r b3acfa50b013 xen/arch/x86/hpet.c
--- a/xen/arch/x86/hpet.c	Sun Jun 13 07:45:17 2010 +0800
+++ b/xen/arch/x86/hpet.c	Sun Jun 13 07:46:32 2010 +0800
@@ -34,7 +34,7 @@ struct hpet_event_channel
     int           shift;
     s_time_t      next_event;
     cpumask_t     cpumask;
-    spinlock_t    cpumask_lock;
+    rwlock_t      cpumask_lock;
     spinlock_t    lock;
     void          (*event_handler)(struct hpet_event_channel *);
 
@@ -197,7 +197,7 @@ again:
     /* find all expired events */
     for_each_cpu_mask(cpu, ch->cpumask)
     {
-        spin_lock_irq(&ch->cpumask_lock);
+        write_lock_irq(&ch->cpumask_lock);
 
         if ( cpumask_test_cpu(cpu, ch->cpumask) )
         {
@@ -207,7 +207,7 @@ again:
                 next_event = per_cpu(timer_deadline_end, cpu);
         }
 
-        spin_unlock_irq(&ch->cpumask_lock);
+        write_unlock_irq(&ch->cpumask_lock);
     }
 
     /* wakeup the cpus which have an expired event. */
@@ -580,7 +580,7 @@ void hpet_broadcast_init(void)
             hpet_events[i].next_event = STIME_MAX;
             hpet_events[i].event_handler = handle_hpet_broadcast;
             spin_lock_init(&hpet_events[i].lock);
-            spin_lock_init(&hpet_events[i].cpumask_lock);
+            rwlock_init(&hpet_events[i].cpumask_lock);
         }
 
         return;
@@ -615,7 +615,7 @@ void hpet_broadcast_init(void)
     legacy_hpet_event.idx = 0;
     legacy_hpet_event.flags = 0;
     spin_lock_init(&legacy_hpet_event.lock);
-    spin_lock_init(&legacy_hpet_event.cpumask_lock);
+    rwlock_init(&legacy_hpet_event.cpumask_lock);
 
     if ( !force_hpet_broadcast )
         pv_rtc_handler = handle_rtc_once;
@@ -692,9 +692,9 @@ void hpet_broadcast_exit(void)
     if ( !reprogram_timer(this_cpu(timer_deadline_start)) )
         raise_softirq(TIMER_SOFTIRQ);
 
-    spin_lock_irq(&ch->cpumask_lock);
+    read_lock_irq(&ch->cpumask_lock);
     cpu_clear(cpu, ch->cpumask);
-    spin_unlock_irq(&ch->cpumask_lock);
+    read_unlock_irq(&ch->cpumask_lock);
 
     if ( ch != &legacy_hpet_event )
     {

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>>> On 17.06.10 at 09:38, "Wei, Gang"
<gang.wei@intel.com> wrote:
> cpuidle: redefine cpumask_lock as rwlock_t
> 
> Multiple cpus clear hpet channel cpumask simultaneously is ok. So we can 
> change the cpumask_lock to rwlock_t.
Now this I think really needs a comment in the code: You use a read
lock on the writer side and a write lock on the reader side - quite the
opposite of normal behavior.

Jan


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On Thursday, 2010-6-17 4:30 PM, Jan Beulich wrote:
>>>> On 17.06.10 at 09:38, "Wei, Gang"
<gang.wei@intel.com> wrote:
>> cpuidle: redefine cpumask_lock as rwlock_t
>> 
>> Multiple cpus clear hpet channel cpumask simultaneously is ok. So we
>> can change the cpumask_lock to rwlock_t.
> 
> Now this I think really needs a comment in the code: You use a read
> lock on the writer side and a write lock on the reader side - quite
> the opposite of normal behavior.
Good suggestion, I will add it.

Jimmy
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