From 2cf4528d6dd6f5a7f34ae07e26176a7932310eeb Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 23 Nov 2021 01:37:06 +0100 Subject: rcu/nocb: Create kthreads on all CPUs if "rcu_nocbs=" or "nohz_full=" are passed In order to be able to (de-)offload any CPU using cpusets in the future, create the NOCB data structures for all possible CPUs. For now this is done only as long as the "rcu_nocbs=" or "nohz_full=" kernel parameters are passed to avoid the unnecessary overhead for most users. Note that the rcuog and rcuoc kthreads are not created until at least one of the corresponding CPUs comes online. This approach avoids the creation of excess kthreads when firmware lies about the number of CPUs present on the system. Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker Cc: Boqun Feng Cc: Uladzislau Rezki Cc: Josh Triplett Cc: Joel Fernandes Tested-by: Juri Lelli Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_nocb.h | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 42092de67705..f580a6b2e74e 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -1237,11 +1237,8 @@ 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) + /* If there already is an rcuo kthread, then nothing to do. */ + if (rdp->nocb_cb_kthread) return; /* If we didn't spawn the GP kthread first, reorganize! */ @@ -1269,7 +1266,7 @@ 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); } @@ -1319,7 +1316,7 @@ 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. */ @@ -1343,7 +1340,8 @@ 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)"); -- cgit v1.2.3-70-g09d2