From 636fed5063dc8a5d0c64bb15bfa13616304415bd Mon Sep 17 00:00:00 2001 From: Keir Fraser Date: Fri, 18 Jun 2010 14:09:44 +0100 Subject: [PATCH] cpuidle: add comments for hpet cpumask_lock usage Signed-off-by: Wei Gang --- xen/arch/x86/hpet.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/xen/arch/x86/hpet.c b/xen/arch/x86/hpet.c index 25e4434cc1..4d9d5a1b61 100644 --- a/xen/arch/x86/hpet.c +++ b/xen/arch/x86/hpet.c @@ -34,6 +34,17 @@ struct hpet_event_channel int shift; s_time_t next_event; cpumask_t cpumask; + /* + * cpumask_lock is used to prevent hpet intr handler from accessing other + * cpu's timer_deadline_start/end after the other cpu's mask was cleared -- + * mask cleared means cpu waken up, then accessing timer_deadline_xxx from + * other cpu is not safe. + * It is not used for protecting cpumask, so set ops needn't take it. + * Multiple cpus clear cpumask simultaneously is ok due to the atomic + * feature of cpu_clear, so hpet_broadcast_exit() can take read lock for + * clearing cpumask, and handle_hpet_broadcast() have to take write lock + * for read cpumask & access timer_deadline_xxx. + */ rwlock_t cpumask_lock; spinlock_t lock; void (*event_handler)(struct hpet_event_channel *); -- 2.30.2