96 lines
3.6 KiB
Diff
96 lines
3.6 KiB
Diff
# HG changeset patch
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# User Jan Beulich <jbeulich@novell.com>
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# Date 1301043797 0
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# Node ID a65612bcbb921e98a8843157bf365e4ab16e8144
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# Parent 941119d58655f2b2df86d9ecc4cb502bbc5e783c
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x86/hpet: eliminate cpumask_lock
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According to the (now getting removed) comment in struct
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hpet_event_channel, this was to prevent accessing a CPU's
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timer_deadline after it got cleared from cpumask. This can be done
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without a lock altogether - hpet_broadcast_exit() can simply clear
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the bit, and handle_hpet_broadcast() can read timer_deadline before
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looking at the mask a second time (the cpumask bit was already
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found set by the surrounding loop).
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Signed-off-by: Jan Beulich <jbeulich@novell.com>
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Acked-by: Gang Wei <gang.wei@intel.com>
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Index: xen-4.1.0-testing/xen/arch/x86/hpet.c
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===================================================================
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--- xen-4.1.0-testing.orig/xen/arch/x86/hpet.c
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+++ xen-4.1.0-testing/xen/arch/x86/hpet.c
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@@ -34,18 +34,6 @@ struct hpet_event_channel
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int shift;
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s_time_t next_event;
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cpumask_t cpumask;
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- /*
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- * cpumask_lock is used to prevent hpet intr handler from accessing other
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- * cpu's timer_deadline after the other cpu's mask was cleared --
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- * mask cleared means cpu waken up, then accessing timer_deadline from
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- * other cpu is not safe.
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- * It is not used for protecting cpumask, so set ops needn't take it.
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- * Multiple cpus clear cpumask simultaneously is ok due to the atomic
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- * feature of cpu_clear, so hpet_broadcast_exit() can take read lock for
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- * clearing cpumask, and handle_hpet_broadcast() have to take write lock
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- * for read cpumask & access timer_deadline.
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- */
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- rwlock_t cpumask_lock;
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spinlock_t lock;
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void (*event_handler)(struct hpet_event_channel *);
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@@ -208,17 +196,18 @@ again:
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/* find all expired events */
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for_each_cpu_mask(cpu, ch->cpumask)
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{
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- write_lock_irq(&ch->cpumask_lock);
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+ s_time_t deadline;
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- if ( cpu_isset(cpu, ch->cpumask) )
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- {
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- if ( per_cpu(timer_deadline, cpu) <= now )
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- cpu_set(cpu, mask);
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- else if ( per_cpu(timer_deadline, cpu) < next_event )
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- next_event = per_cpu(timer_deadline, cpu);
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- }
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+ rmb();
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+ deadline = per_cpu(timer_deadline, cpu);
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+ rmb();
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+ if ( !cpu_isset(cpu, ch->cpumask) )
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+ continue;
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- write_unlock_irq(&ch->cpumask_lock);
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+ if ( deadline <= now )
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+ cpu_set(cpu, mask);
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+ else if ( deadline < next_event )
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+ next_event = deadline;
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}
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/* wakeup the cpus which have an expired event. */
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@@ -598,7 +587,6 @@ void hpet_broadcast_init(void)
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hpet_events[i].shift = 32;
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hpet_events[i].next_event = STIME_MAX;
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spin_lock_init(&hpet_events[i].lock);
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- rwlock_init(&hpet_events[i].cpumask_lock);
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wmb();
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hpet_events[i].event_handler = handle_hpet_broadcast;
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}
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@@ -634,7 +622,6 @@ void hpet_broadcast_init(void)
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legacy_hpet_event.idx = 0;
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legacy_hpet_event.flags = 0;
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spin_lock_init(&legacy_hpet_event.lock);
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- rwlock_init(&legacy_hpet_event.cpumask_lock);
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wmb();
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legacy_hpet_event.event_handler = handle_hpet_broadcast;
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@@ -716,9 +703,7 @@ void hpet_broadcast_exit(void)
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if ( !reprogram_timer(this_cpu(timer_deadline)) )
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raise_softirq(TIMER_SOFTIRQ);
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- read_lock_irq(&ch->cpumask_lock);
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cpu_clear(cpu, ch->cpumask);
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- read_unlock_irq(&ch->cpumask_lock);
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if ( ch != &legacy_hpet_event )
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{
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