2012/8/31 Josh Triplett <[email protected]>: > On Thu, Aug 30, 2012 at 02:05:19PM -0700, Paul E. McKenney wrote: >> From: Frederic Weisbecker <[email protected]> >> >> In some cases, it is necessary to enter or exit userspace-RCU-idle mode >> from an interrupt handler, for example, if some other CPU sends this >> CPU a resched IPI. In this case, the current CPU would enter the IPI >> handler in userspace-RCU-idle mode, but would need to exit the IPI handler >> after having exited that mode. >> >> To allow this to work, this commit adds two new APIs to TREE_RCU: >> >> - rcu_user_enter_irq(). This must be called from an interrupt between >> rcu_irq_enter() and rcu_irq_exit(). After the irq calls rcu_irq_exit(), >> the irq handler will return into an RCU extended quiescent state. >> In theory, this interrupt is never a nested interrupt, but in practice >> it might interrupt softirq, which looks to RCU like a nested interrupt. >> >> - rcu_user_exit_irq(). This must be called from a non-nesting >> interrupt, interrupting an RCU extended quiescent state, also >> between rcu_irq_enter() and rcu_irq_exit(). After the irq calls >> rcu_irq_exit(), the irq handler will return in an RCU non-quiescent >> state. > > These names seem a bit confusing. From the descriptions, it sounds like > you don't always need to pair them; rcu_irq_exit() will return to a > non-quiescent state, unless you call rcu_user_enter_irq and *don't* call > rcu_user_exit_irq. Did I get that semantic right?
Yeah. They indeed don't always need to be paired. We can enter into user (from rcu POV) with rcu_user_enter_irq() and exit user with rcu_user_exit(). It's just a matter of context: from where do we set/unset RCU as in user mode: irq or not. The only thing that is paired is the fact we enter/exit that RCU user mode. There are just different APIs to do so. > Given that, the "enter" and "exit" names seem confusing. This seems > more like a flag you can set and clear, rather than a delimited region > as suggested by an enter/exit pair. > > How about something vaguely like rcu_user_irq_set_eqs and > rcu_user_irq_clear_eqs? I'd rather suggest rcu_user_enter_after_irq and rcu_user_exit_after_irq. It describes precisely what it does. > > - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
