Messages in this thread | | | Date | Tue, 26 Jun 2018 05:31:49 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 2/2] rcu: Make expedited GPs handle CPU 0 being offline |
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On Tue, Jun 26, 2018 at 07:46:52PM +0800, Boqun Feng wrote: > On Tue, Jun 26, 2018 at 06:44:47PM +0800, Boqun Feng wrote: > > On Tue, Jun 26, 2018 at 11:38:20AM +0200, Peter Zijlstra wrote: > > > On Mon, Jun 25, 2018 at 03:43:32PM -0700, Paul E. McKenney wrote: > > > > + preempt_disable(); > > > > + for_each_leaf_node_possible_cpu(rnp, cpu) { > > > > + if (cpu_is_offline(cpu)) /* Preemption disabled. */ > > > > + continue; > > > > > > Create for_each_node_online_cpu() instead? Seems a bit pointless to > > > iterate possible mask only to then check it against the online mask. > > > Just iterate the online mask directly. > > > > > > Or better yet, write this as: > > > > > > preempt_disable(); > > > cpu = cpumask_next(rnp->grplo - 1, cpu_online_mask); > > > if (cpu > rnp->grphi) > > > cpu = WORK_CPU_UNBOUND; > > > queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work); > > > preempt_enable(); > > > > > > Which is what it appears to be doing. > > > > > > > Make sense! Thanks ;-) > > > > Applied this and running a TREE03 rcutorture. If all go well, I will > > send the updated patch. > > So the patch has passed one 30 min run for TREE03 rcutorture. Paul, > if it looks good, could you take it for your next spin or pull request > in the future? Thanks.
Looks much improved, thank you both! I will pull this in later today, Pacific Time.
Thanx, Paul
> Regards, > Boqun > > -------------->8 > Subject: [PATCH tip/core/rcu v2] rcu: exp: Make expedited GPs handle CPU 0 being offline > > Currently, the parallelized initialization of expedited grace periods > uses the workqueue associated with each rcu_node structure's ->grplo > field. This works fine unless that CPU is offline. This commit > therefore uses the CPU corresponding to the lowest-numbered online CPU, > or fallback to queue the work on WORK_CPU_UNBOUND if there are no online > CPUs on this rcu_node structure. > > Note that this patch uses cpu_online_mask instead of the usual approach > of checking bits in the rcu_node structure's ->qsmaskinitnext field. > This is safe because preemption is disabled across both the > cpu_online_mask check and the call to queue_work_on(). > > Signed-off-by: Boqun Feng <boqun.feng@gmail.com> > [ paulmck: Disable preemption to close offline race window. ] > Not-Yet-Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > --- > v1 --> v2: > > * Replace the for_each_leaf_node_possible_cpu() + cpu_is_offline() > check loop with a single cpumask_next() as suggested by Peter > Zijlstra > > kernel/rcu/tree_exp.h | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h > index d40708e8c5d6..3bf87fd4bd91 100644 > --- a/kernel/rcu/tree_exp.h > +++ b/kernel/rcu/tree_exp.h > @@ -473,6 +473,7 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, > smp_call_func_t func) > { > struct rcu_node *rnp; > + int cpu; > > trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("reset")); > sync_exp_reset_tree(rsp); > @@ -492,7 +493,13 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, > continue; > } > INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus); > - queue_work_on(rnp->grplo, rcu_par_gp_wq, &rnp->rew.rew_work); > + preempt_disable(); > + cpu = cpumask_next(rnp->grplo - 1, cpu_online_mask); > + /* All offlines, queue the work on an unbound CPU */ > + if (unlikely(cpu > rnp->grphi)) > + cpu = WORK_CPU_UNBOUND; > + queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work); > + preempt_enable(); > rnp->exp_need_flush = true; > } > > -- > 2.17.1 >
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