Messages in this thread | | | Date | Fri, 3 May 2013 10:52:36 +0300 (EEST) | From | Julian Anastasov <> | Subject | Re: [PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper |
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Hello,
On Thu, 2 May 2013, Paul E. McKenney wrote:
> mainline, and missed the one that you added. Revisiting that, a > question: > > > +#ifdef CONFIG_PREEMPT_RCU > > +#define PREEMPT_RCU_OFFSET 1 > > Does this really want to be "1" instead of PREEMPT_OFFSET?
In this case when CONFIG_PREEMPT_RCU is enabled we (RCU) do not touch the preempt counters. Instead, the units are accounted in current->rcu_read_lock_nesting:
#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
__rcu_read_lock: current->rcu_read_lock_nesting++;
and the path is __might_sleep -> preempt_count_equals -> rcu_preempt_depth
For now both places do not use PREEMPT_OFFSET:
- #define inc_preempt_count() add_preempt_count(1) - __rcu_read_lock: current->rcu_read_lock_nesting++;
so, ... it does not matter much for me. In short, the trick is in preempt_count_equals() where preempt_offset is a combination of preempt count and RCU preempt depth:
#ifdef CONFIG_PREEMPT_RCU #define PREEMPT_RCU_OFFSET (0 /* preempt */ + 1 /* RCU */) #else #define PREEMPT_RCU_OFFSET (PREEMPT_CHECK_OFFSET + 0 /* RCU */) #endif
Let me know for your preference about this definition...
Regards
-- Julian Anastasov <ja@ssi.bg>
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