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Date: Thu, 2 Feb 2012 09:48:12 -0800 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Josh Triplett <josh@...htriplett.org> Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com, patches@...aro.org, "Paul E. McKenney" <paul.mckenney@...aro.org> Subject: Re: [PATCH RFC tip/core/rcu 22/41] rcu: Simplify unboosting checks On Wed, Feb 01, 2012 at 06:38:47PM -0800, Josh Triplett wrote: > On Wed, Feb 01, 2012 at 11:41:40AM -0800, Paul E. McKenney wrote: > > From: "Paul E. McKenney" <paul.mckenney@...aro.org> > > > > This is a port of commit #82e78d80 from TREE_PREEMPT_RCU to > > TINY_PREEMPT_RCU. > > > > This commit uses the fact that current->rcu_boost_mutex is set > > any time that the RCU_READ_UNLOCK_BOOSTED flag is set in the > > current->rcu_read_unlock_special bitmask. This allows tests of > > the bit to be changed to tests of the pointer, which in turn allows > > the RCU_READ_UNLOCK_BOOSTED flag to be eliminated. > > Does this change affect rcu_read_unlock()'s logic to trigger the > slowpath only when special flags get set? Interestingly enough, it does not. The only way a task can be subjected to RCU priority boosting is for that task to block sometime in its current RCU read-side critical section. When the task blocks, the RCU_READ_UNLOCK_BLOCKED flag will be set. Therefore, any time that the current->rcu_boost_mutex pointer is non-NULL, the RCU_READ_UNLOCK_BLOCKED flag will be set, so the current test of current->rcu_read_unlock_special against zero continues to work correctly. OK, OK, I will update the commit message with words to this effect. ;-) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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