Messages in this thread | | | Date | Wed, 1 Jul 2015 07:03:13 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC tip/core/rcu 2/5] rcu: Short-circuit normal GPs via expedited GPs |
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On Wed, Jul 01, 2015 at 03:48:06PM +0200, Peter Zijlstra wrote: > On Wed, Jul 01, 2015 at 06:41:44AM -0700, Paul E. McKenney wrote: > > On Wed, Jul 01, 2015 at 12:05:21PM +0200, Peter Zijlstra wrote: > > > On Tue, Jun 30, 2015 at 02:48:27PM -0700, Paul E. McKenney wrote: > > > > rsp->gp_state = RCU_GP_WAIT_FQS; > > > > ret = wait_event_interruptible_timeout(rsp->gp_wq, > > > > + ((gf = READ_ONCE(rsp->gp_flags)) & > > > > + RCU_GP_FLAG_FQS) || > > > > + (!READ_ONCE(rnp->qsmask) && > > > > + !rcu_preempt_blocked_readers_cgp(rnp)) || > > > > + rcu_exp_gp_seq_done(rsp->exp_rsp, > > > > + rsp->gp_exp_snap), > > > > + j); > > > > rsp->gp_state = RCU_GP_DONE_FQS; > > > > > > How can the GP be done if we timed out or got interrupted? > > > > If all the CPUs still blocking the grace period went idle, or in a > > NO_HZ_FULL kernel, entered nohz_full userspace execution. Or, if > > certain low-probability races happen, went offline. > > But what if none of those are true and we still timed out? You > unconditionally grant the GP.
Say what???
I recheck the conditions and break out of the loop only if one or more of the grace-period-end conditions is satisfied. If not, I invoke rcu_gp_fqs() to do the scan to see if all remaining CPUs are idle, in nohz_full userspace execution, or offline.
What am I mising here?
Thanx, Paul
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