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Hello,
On Mon, 29 Apr 2013, Paul E. McKenney wrote:
> On Tue, Apr 30, 2013 at 12:08:18AM +0300, Julian Anastasov wrote:
> >
> > Hello,
> >
> > On Sat, 27 Apr 2013, Paul E. McKenney wrote:
> >
> > > I would instead suggest something like:
> > >
> > > #ifndef CONFIG_PREEMPT_RCU
> > >
> > > But yes, in the CONFIG_PREEMPT_RCU case, the cond_resched() is not
> > > needed.
> >
> > Hm, is this correct? If I follow the ifdefs
> > preempt_schedule is called when CONFIG_PREEMPT is
> > defined _and_ CONFIG_PREEMPT_RCU is not defined.
> > Your example for CONFIG_PREEMPT_RCU is the opposite to this?
>
> Yep, I really did intend to say "#ifndef CONFIG_PREEMPT_RCU".
>
> A couple of things to keep in mind:
>
> 1. Although rcu_read_unlock() does map to preempt_enable() for
> CONFIG_TINY_RCU and CONFIG_TREE_RCU, the current Kconfig refuses
> to allow either CONFIG_TINY_RCU or CONFIG_TREE_RCU to be selected
> if CONFIG_PREEMPT=y.
I see, CONFIG_PREEMPT_RCU depends on CONFIG_PREEMPT
> 2. In the CONFIG_PREEMPT_RCU case, __rcu_read_unlock() will check
> to see if the RCU core needs to be informed, so there is no
> need to invoke cond_resched() in that case.
OK
> 3. If we drop your "|| defined(CONFIG_PREEMPT_RCU)", we get an
> almost-synonym for my "#ifndef CONFIG_PREEMPT_RCU". The "almost"
> applies to older kernels due to the possibility of having a
> CONFIG_TINY_PREEMPT_RCU kernel -- but this possibility is going
> away soon.
>
> Make sense?
Yes, thanks for the explanation!
Simon, so lets do it as suggested by Eric and Paul:
rcu_read_unlock();
#ifndef CONFIG_PREEMPT_RCU
cond_resched();
#endif
rcu_read_lock();
Regards
--
Julian Anastasov <ja@xxxxxx>
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