Hello,
On Wed, 1 May 2013, Peter Zijlstra wrote:
> On Wed, May 01, 2013 at 05:22:05PM +0300, Julian Anastasov wrote:
>
> > 2. Same without need_resched because cond_resched already
> > performs the same checks:
> >
> > static void inline cond_resched_rcu_lock(void)
> > {
> > #ifndef CONFIG_PREEMPT_RCU
> > rcu_read_unlock();
> > cond_resched();
> > rcu_read_lock();
> > #endif
> > }
>
> Ah so the 'problem' with this last version is that it does an unconditional /
> unnessecary rcu_read_unlock().
It is just a barrier() for the non-preempt case.
> The below would be in line with all the other cond_resched*() implementations.
...
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 802a751..fd2c77f 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2449,6 +2449,13 @@ extern int __cond_resched_softirq(void);
> __cond_resched_softirq(); \
> })
>
> +extern int __cond_resched_rcu(void);
> +
> +#define cond_resched_rcu() ({ \
> + __might_sleep(__FILE__, __LINE__, 0); \
I see your goal. But digging into __might_sleep()
I see that rcu_sleep_check() will scream for the non-preempt
case because we are under rcu_read_lock.
What about such inline version:
static void inline cond_resched_rcu(void)
{
#ifndef CONFIG_PREEMPT_RCU
rcu_read_unlock();
__might_sleep(__FILE__, __LINE__, 0);
cond_resched();
rcu_read_lock();
#else
__might_sleep(__FILE__, __LINE__, 0);
rcu_lockdep_assert(rcu_preempt_depth() == 1,
"Illegal cond_resched_rcu() context");
#endif
}
It will restrict to single RCU lock level for all
RCU implementations. But we don't have _cond_resched_rcu
helper for two reasons:
- __might_sleep uses __FILE__, __LINE__
- only cond_resched generates code, so need_resched() is
avoided
> + __cond_resched_rcu(); \
> +})
> +
> /*
> * Does a critical section need to be broken due to another
> * task waiting?: (technically does not depend on CONFIG_PREEMPT,
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 7d7901a..2b3b4e6 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4358,6 +4358,20 @@ int __sched __cond_resched_softirq(void)
> }
> EXPORT_SYMBOL(__cond_resched_softirq);
>
> +int __sched __cond_resched_rcu(void)
> +{
> +#ifndef CONFIG_PREEMPT_RCU
> + if (should_resched()) {
> + rcu_read_unlock();
> + __cond_resched();
> + rcu_read_lock();
> + return 1;
> + }
> +#endif
> + return 0;
> +}
> +EXPORT_SYMBOL(__cond_resched_rcu);
> +
Regards
--
Julian Anastasov <ja@xxxxxx>
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