Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753168AbaGKNiZ (ORCPT ); Fri, 11 Jul 2014 09:38:25 -0400 Received: from e38.co.us.ibm.com ([32.97.110.159]:44427 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751667AbaGKNiX (ORCPT ); Fri, 11 Jul 2014 09:38:23 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, sbw@mit.edu, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 2/2] rcu: Don't offload callbacks unless specifically requested Date: Fri, 11 Jul 2014 06:35:03 -0700 Message-Id: <1405085703-14822-2-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1405085703-14822-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20140707224841.GA10101@linux.vnet.ibm.com> <1405085703-14822-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14071113-1344-0000-0000-000002C3406F Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" Enabling NO_HZ_FULL currently has the side effect of enabling callback offloading on all CPUs. This results in lots of additional rcuo kthreads, and can also increase context switching and wakeups, even in cases where callback offloading is neither needed nor particularly desirable. This commit therefore enables callback offloading on a given CPU only if specifically requested at build time or boot time, or if that CPU has been specifically designated (again, either at build time or boot time) as a nohz_full CPU. Signed-off-by: Paul E. McKenney --- init/Kconfig | 4 ++-- kernel/rcu/tree_plugin.h | 3 +++ 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 9d76b99af1b9..9332d33346ac 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -737,7 +737,7 @@ choice config RCU_NOCB_CPU_NONE bool "No build_forced no-CBs CPUs" - depends on RCU_NOCB_CPU && !NO_HZ_FULL + depends on RCU_NOCB_CPU && !NO_HZ_FULL_ALL help This option does not force any of the CPUs to be no-CBs CPUs. Only CPUs designated by the rcu_nocbs= boot parameter will be @@ -751,7 +751,7 @@ config RCU_NOCB_CPU_NONE config RCU_NOCB_CPU_ZERO bool "CPU 0 is a build_forced no-CBs CPU" - depends on RCU_NOCB_CPU && !NO_HZ_FULL + depends on RCU_NOCB_CPU && !NO_HZ_FULL_ALL help This option forces CPU 0 to be a no-CBs CPU, so that its RCU callbacks are invoked by a per-CPU kthread whose name begins diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index b27b86c7bbfa..17eed0856b03 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2473,6 +2473,9 @@ static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) if (rcu_nocb_mask == NULL) return; +#ifdef CONFIG_NO_HZ_FULL + cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); +#endif /* #ifdef CONFIG_NO_HZ_FULL */ if (ls == -1) { ls = int_sqrt(nr_cpu_ids); rcu_nocb_leader_stride = ls; -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/