Messages in this thread Patch in this message | | | Date | Mon, 3 Jan 2022 06:34:42 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] rcu: per-cpu rcuc kthread are created only when rcutree.use_softirq=0 |
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On Mon, Jan 03, 2022 at 02:17:11PM +0100, Sebastian Andrzej Siewior wrote: > On 2022-01-01 08:44:26 [-0800], Paul E. McKenney wrote: > > On Wed, Dec 29, 2021 at 12:05:10AM +0800, Zqiang wrote: > > > In non-RT kernel, if the RCU_BOOST is enabled, the per-cpu rcuc > > > kthread will be created, however under the rcutree.use_softirq=1, > > > the RCU core processing only in softirq context, the rcuc kthread > > > doesn't do anything, so remove RCU_BOOST interference. > > > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > > > Looks sane to me, but adding Sebastian on CC for his thoughts. > > Yes, it makes sense. invoke_rcu_core_kthread() is only invoked for > !use_softirq so it makes to create the threads based on this condition. > > Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Thank you both! As usual, I could not resist a bit of wordsmithing, please see below.
Thanx, Paul
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commit 6e68b781388cfaca95a07493a060c4a6e4ee5d0f Author: Zqiang <qiang1.zhang@intel.com> Date: Wed Dec 29 00:05:10 2021 +0800
rcu: Create per-cpu rcuc kthreads only when rcutree.use_softirq=0 The per-CPU "rcuc" kthreads are used only by kernels booted with rcutree.use_softirq=0, but they are nevertheless unconditionally created by kernels built with CONFIG_RCU_BOOST=y. This results in "rcuc" kthreads being created that are never actually used. This commit therefore refrains from creating these kthreads unless the kernel is actually booted with rcutree.use_softirq=0. Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Zqiang <qiang1.zhang@intel.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index aeea5487632f7..5c0ffee7a43a0 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2903,7 +2903,7 @@ static int __init rcu_spawn_core_kthreads(void) for_each_possible_cpu(cpu) per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0; - if (!IS_ENABLED(CONFIG_RCU_BOOST) && use_softirq) + if (use_softirq) return 0; WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__);
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