From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E31CAC433EF for ; Fri, 13 May 2022 00:16:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241086AbiEMAQZ (ORCPT ); Thu, 12 May 2022 20:16:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33086 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1359172AbiEMAQY (ORCPT ); Thu, 12 May 2022 20:16:24 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7BA3A4FC76 for ; Thu, 12 May 2022 17:16:23 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1847362097 for ; Fri, 13 May 2022 00:16:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 72AB1C385B8; Fri, 13 May 2022 00:16:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1652400982; bh=4KJTmceKNZnl2JDVf0Yp2kcvX0hp3uXG+h7t2UXi47g=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=FZc8Mqjl9bzWMqe3o9pHZUmMC/tdDlDuNGUG527WE2RrTSeR1zDcaOcPP/qKCkitv qmp8jH2Wog5l43kcMhptcF0eJqZF1ugM7Hor83dwttXsqG5V6XglYG2DGXab56A8Cl 8e2Ady26qbVKvxvKYDpcqN0j67MsfKuuIsPtWs3xIIbHO9K62kYwKjrxMqSHEqlMcQ O82e3+uezj0A+F4WX5peS3IyO8tsqK3NqhlQ1plmNdKSIyU/GphxyacDQMoizmlG3D FcnPlM83dId+iD04HkuKqUE4GLNQ2/dwwnMNbGnIr9djT15JRhkPbhdI+W1PevT24J 3jH+3pfX8gaZw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 0FDEC5C051B; Thu, 12 May 2022 17:16:22 -0700 (PDT) Date: Thu, 12 May 2022 17:16:22 -0700 From: "Paul E. McKenney" To: "Joel Fernandes (Google)" Cc: rcu@vger.kernel.org, rushikesh.s.kadam@intel.com, urezki@gmail.com, neeraj.iitr10@gmail.com, frederic@kernel.org, rostedt@goodmis.org Subject: Re: [RFC v1 14/14] DEBUG: Toggle rcu_lazy and tune at runtime Message-ID: <20220513001622.GA1790663@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220512030442.2530552-1-joel@joelfernandes.org> <20220512030442.2530552-15-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220512030442.2530552-15-joel@joelfernandes.org> Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Thu, May 12, 2022 at 03:04:42AM +0000, Joel Fernandes (Google) wrote: > Add sysctl knobs just for easier debugging/testing, to tune the maximum > batch size, maximum time to wait before flush, and turning off the > feature entirely. > > Signed-off-by: Joel Fernandes (Google) This is good, and might also be needed longer term. One thought below. Thanx, Paul > --- > include/linux/sched/sysctl.h | 4 ++++ > kernel/rcu/lazy.c | 12 ++++++++++-- > kernel/sysctl.c | 23 +++++++++++++++++++++++ > 3 files changed, 37 insertions(+), 2 deletions(-) > > diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h > index c19dd5a2c05c..55ffc61beed1 100644 > --- a/include/linux/sched/sysctl.h > +++ b/include/linux/sched/sysctl.h > @@ -16,6 +16,10 @@ enum { sysctl_hung_task_timeout_secs = 0 }; > > extern unsigned int sysctl_sched_child_runs_first; > > +extern unsigned int sysctl_rcu_lazy; > +extern unsigned int sysctl_rcu_lazy_batch; > +extern unsigned int sysctl_rcu_lazy_jiffies; > + > enum sched_tunable_scaling { > SCHED_TUNABLESCALING_NONE, > SCHED_TUNABLESCALING_LOG, > diff --git a/kernel/rcu/lazy.c b/kernel/rcu/lazy.c > index 55e406cfc528..0af9fb67c92b 100644 > --- a/kernel/rcu/lazy.c > +++ b/kernel/rcu/lazy.c > @@ -12,6 +12,10 @@ > // How much to wait before flushing? > #define MAX_LAZY_JIFFIES 10000 > > +unsigned int sysctl_rcu_lazy_batch = MAX_LAZY_BATCH; > +unsigned int sysctl_rcu_lazy_jiffies = MAX_LAZY_JIFFIES; > +unsigned int sysctl_rcu_lazy = 1; > + > // We cast lazy_rcu_head to rcu_head and back. This keeps the API simple while > // allowing us to use lockless list node in the head. Also, we use BUILD_BUG_ON > // later to ensure that rcu_head and lazy_rcu_head are of the same size. > @@ -49,6 +53,10 @@ void call_rcu_lazy(struct rcu_head *head_rcu, rcu_callback_t func) > struct lazy_rcu_head *head = (struct lazy_rcu_head *)head_rcu; > struct rcu_lazy_pcp *rlp; > > + if (!sysctl_rcu_lazy) { This is the place to check for early boot use. Or, alternatively, initialize sysctl_rcu_lazy to zero and set it to one once boot is far enough along to allow all the pieces to work reasonably. > + return call_rcu(head_rcu, func); > + } > + > preempt_disable(); > rlp = this_cpu_ptr(&rcu_lazy_pcp_ins); > preempt_enable(); > @@ -67,11 +75,11 @@ void call_rcu_lazy(struct rcu_head *head_rcu, rcu_callback_t func) > llist_add(&head->llist_node, &rlp->head); > > // Flush queue if too big > - if (atomic_inc_return(&rlp->count) >= MAX_LAZY_BATCH) { > + if (atomic_inc_return(&rlp->count) >= sysctl_rcu_lazy_batch) { > lazy_rcu_flush_cpu(rlp); > } else { > if (!delayed_work_pending(&rlp->work)) { > - schedule_delayed_work(&rlp->work, MAX_LAZY_JIFFIES); > + schedule_delayed_work(&rlp->work, sysctl_rcu_lazy_jiffies); > } > } > } > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 5ae443b2882e..2ba830ca71ec 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -1659,6 +1659,29 @@ static struct ctl_table kern_table[] = { > .mode = 0644, > .proc_handler = proc_dointvec, > }, > +#ifdef CONFIG_RCU_LAZY > + { > + .procname = "rcu_lazy", > + .data = &sysctl_rcu_lazy, > + .maxlen = sizeof(unsigned int), > + .mode = 0644, > + .proc_handler = proc_dointvec, > + }, > + { > + .procname = "rcu_lazy_batch", > + .data = &sysctl_rcu_lazy_batch, > + .maxlen = sizeof(unsigned int), > + .mode = 0644, > + .proc_handler = proc_dointvec, > + }, > + { > + .procname = "rcu_lazy_jiffies", > + .data = &sysctl_rcu_lazy_jiffies, > + .maxlen = sizeof(unsigned int), > + .mode = 0644, > + .proc_handler = proc_dointvec, > + }, > +#endif > #ifdef CONFIG_SCHEDSTATS > { > .procname = "sched_schedstats", > -- > 2.36.0.550.gb090851708-goog >