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Message-ID: <20151007154457.GL3910@linux.vnet.ibm.com> Date: Wed, 7 Oct 2015 08:44:57 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Peter Zijlstra <peterz@...radead.org> Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com Subject: Re: [PATCH tip/core/rcu 04/18] rcu: Use single-stage IPI algorithm for RCU expedited grace period On Wed, Oct 07, 2015 at 03:35:45PM +0200, Peter Zijlstra wrote: > On Tue, Oct 06, 2015 at 09:29:23AM -0700, Paul E. McKenney wrote: > > > +/* Flags for rcu_preempt_ctxt_queue() decision table. */ > > +#define RCU_GP_TASKS 0x8 > > +#define RCU_EXP_TASKS 0x4 > > +#define RCU_GP_BLKD 0x2 > > +#define RCU_EXP_BLKD 0x1 > > Purely cosmetic, but that's backwards ;-) Most of our flags etc.. are in > increasing order. > > > +static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp, > > + unsigned long flags) __releases(rnp->lock) > > +{ > > + int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) + > > + (rnp->exp_tasks ? RCU_EXP_TASKS : 0) + > > + (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) + > > + (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0); > > An alternative way is: > > int blkd_state = RCU_GP_TASKS * !!rnp->gp_tasks + > RCU_EXP_TASKS * !!rnp->exp_tasks + > RCU_GP_BLKD * !!(rnp->qsmask & rdp->grpmask) + > RCU_EXP_BLKD * !!(rnp->expmask & rdp->grpmask); > > I suppose it depends on how your brain is wired which version reads > easier :-) Indeed! ;-) I will stick with the ?: for the moment, but your multiplied bang-up approach might well grow on me. 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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