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Date: Wed, 30 Apr 2014 11:04:20 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Davidlohr Bueso <davidlohr@...com> Cc: Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Tim Chen <tim.c.chen@...ux.intel.com>, Andrea Arcangeli <aarcange@...hat.com>, Alex Shi <alex.shi@...aro.org>, Andi Kleen <andi@...stfloor.org>, Michel Lespinasse <walken@...gle.com>, Rik van Riel <riel@...hat.com>, Peter Hurley <peter@...leysoftware.com>, Thomas Gleixner <tglx@...utronix.de>, "Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>, Aswin Chandramouleeswaran <aswin@...com>, "Norton, Scott J" <scott.norton@...com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2] rwsem: Support optimistic spinning On Mon, Apr 28, 2014 at 03:09:01PM -0700, Davidlohr Bueso wrote: > +static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) > +{ > + int retval; And yet the return value is bool. > + struct task_struct *owner; > + > + rcu_read_lock(); > + owner = ACCESS_ONCE(sem->owner); > + > + /* Spin only if active writer running */ > + if (owner) > + retval = owner->on_cpu; > + else { > + /* > + * When the owner is not set, the sem owner may have just > + * acquired it and not set the owner yet, or the sem has > + * been released, or reader active. > + */ > + retval = false; > + } And if you init the retval to false, you can leave this entire branch out. > + rcu_read_unlock(); > + > + return retval; > +} Which yields the much shorter: static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) { struct task_struct *owner; bool on_cpu = false; rcu_read_lock(); owner = ACCESS_ONCE(sem->owner); if (owner) on_cpu = owner->on_cpu; rcu_read_unlock(); return on_cpu; } -- 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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