Messages in this thread | | | Date | Wed, 1 Dec 2021 14:57:18 +0530 | Subject | Re: [PATCH 4/6] rcu/nocb: Create kthreads on all CPUs if "rcu_nocb=" or "nohz_full=" are passed | From | Neeraj Upadhyay <> |
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On 11/23/2021 6:07 AM, Frederic Weisbecker wrote: > In order to be able to (de-)offload any CPU using cpuset in the future, > create a NOCB kthread for all possible CPUs. For now this is done only > as long as the "rcu_nocb=" or "nohz_full=" kernel parameters are passed > to avoid the unnecessary overhead for most users. > > Signed-off-by: Frederic Weisbecker <frederic@kernel.org> > Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com> > Cc: Boqun Feng <boqun.feng@gmail.com> > Cc: Uladzislau Rezki <urezki@gmail.com> > Cc: Josh Triplett <josh@joshtriplett.org> > Cc: Joel Fernandes <joel@joelfernandes.org> > ---
Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
> kernel/rcu/tree_nocb.h | 14 ++++++-------- > 1 file changed, 6 insertions(+), 8 deletions(-) > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > index d8ed3ee47a67..9d37916278d4 100644 > --- a/kernel/rcu/tree_nocb.h > +++ b/kernel/rcu/tree_nocb.h > @@ -1229,11 +1229,8 @@ static void rcu_spawn_one_nocb_kthread(int cpu) > struct rcu_data *rdp_gp; > struct task_struct *t; > > - /* > - * If this isn't a no-CBs CPU or if it already has an rcuo kthread, > - * then nothing to do. > - */ > - if (!rcu_is_nocb_cpu(cpu) || rdp->nocb_cb_kthread)
As rcu_is_nocb_cpu() does not have a user, we can probably remove it?
Thanks Neeraj
> + /* If it already has an rcuo kthread, then nothing to do. */ > + if (rdp->nocb_cb_kthread) > return; > > /* If we didn't spawn the GP kthread first, reorganize! */ > @@ -1261,7 +1258,7 @@ static void rcu_spawn_one_nocb_kthread(int cpu) > */ > static void rcu_spawn_cpu_nocb_kthread(int cpu) > { > - if (rcu_scheduler_fully_active) > + if (rcu_scheduler_fully_active && rcu_nocb_is_setup) > rcu_spawn_one_nocb_kthread(cpu); > } > > @@ -1311,7 +1308,7 @@ static void __init rcu_organize_nocb_kthreads(void) > * Should the corresponding CPU come online in the future, then > * we will spawn the needed set of rcu_nocb_kthread() kthreads. > */ > - for_each_cpu(cpu, rcu_nocb_mask) { > + for_each_possible_cpu(cpu) { > rdp = per_cpu_ptr(&rcu_data, cpu); > if (rdp->cpu >= nl) { > /* New GP kthread, set up for CBs & next GP. */ > @@ -1335,7 +1332,8 @@ static void __init rcu_organize_nocb_kthreads(void) > pr_cont(" %d", cpu); > } > rdp->nocb_gp_rdp = rdp_gp; > - list_add_tail(&rdp->nocb_entry_rdp, &rdp_gp->nocb_head_rdp); > + if (cpumask_test_cpu(cpu, rcu_nocb_mask)) > + list_add_tail(&rdp->nocb_entry_rdp, &rdp_gp->nocb_head_rdp); > } > if (gotnocbs && dump_tree) > pr_cont("%s\n", gotnocbscbs ? "" : " (self only)"); >
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