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 1B68EC433FE for ; Tue, 8 Mar 2022 18:14:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349450AbiCHSO5 (ORCPT ); Tue, 8 Mar 2022 13:14:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32906 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245396AbiCHSOz (ORCPT ); Tue, 8 Mar 2022 13:14:55 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CB7BF424B8; Tue, 8 Mar 2022 10:13:58 -0800 (PST) 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 ams.source.kernel.org (Postfix) with ESMTPS id 54E01B818A0; Tue, 8 Mar 2022 18:13:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id ED91CC340EB; Tue, 8 Mar 2022 18:13:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1646763236; bh=utWdFLKhIY9H7mCT5rLTLSg7JMStuWY6SjN2JIaKlVY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=shOITVqGGgNqINBi9zc5HslKM4Y8NOHES1H3f6bMlYNGCChX94dzTRc+j3+IdjOOD BY5p7Ej0E/mKJgfpgVokRGWMLsCuadsqJSTLBVqdvsc7hlJ+wWPsXX/75Hj9Y7wits LgyrScl08vuechGdexgJy7Nra2pADNgDbzcO3kyriIiBSnu0uT90gDMn+dRJR85hfD 95zQDbuQqnrbuKvib1sqv2X1AfLMUHhrHPsEk0i33CTSsuzj0pcW04xhU86pnN0qL1 z1YU0BSs5C/JZGw3do8AHnq1fe34+zDxQ0kWTfwDyyr373yX4VVos516AuUzZXzHl7 cWVjkGYAp1G9A== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 934F85C08A0; Tue, 8 Mar 2022 10:13:55 -0800 (PST) Date: Tue, 8 Mar 2022 10:13:55 -0800 From: "Paul E. McKenney" To: Uladzislau Rezki Cc: "Zhang, Qiang1" , Neeraj Upadhyay , "frederic@kernel.org" , "linux-kernel@vger.kernel.org" , rcu@vger.kernel.org, bigeasy@linutronix.de, juri.lelli@redhat.com Subject: Re: [PATCH] rcu: Only boost rcu reader tasks with lower priority than boost kthreads Message-ID: <20220308181355.GW4285@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220304092631.4123188-1-qiang1.zhang@intel.com> <81f69dd4-6ca9-760c-bec5-5cb27afbe788@quicinc.com> <20220307191512.GN4285@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 08, 2022 at 07:04:21PM +0100, Uladzislau Rezki wrote: > > On Mon, Mar 07, 2022 at 02:03:17AM +0000, Zhang, Qiang1 wrote: > > > On 3/4/2022 2:56 PM, Zqiang wrote: > > > > When RCU_BOOST is enabled, the boost kthreads will boosting readers > > > > who are blocking a given grace period, if the current reader tasks > > > > have a higher priority than boost kthreads(the boost kthreads priority > > > > not always 1, if the kthread_prio is set), boosting is useless, skip > > > > current task and select next task to boosting, reduce the time for a > > > > given grace period. > > > > > > > > Signed-off-by: Zqiang > > > > Adding to CC to get more eyes on this. I am not necessarily opposed to > > it, but I don't do that much RT work myself these days. > > > > Thanx, Paul > > > > > > --- > > > > kernel/rcu/tree_plugin.h | 10 +++++++++- > > > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > > > > index c3d212bc5338..d35b6da66bbd 100644 > > > > --- a/kernel/rcu/tree_plugin.h > > > > +++ b/kernel/rcu/tree_plugin.h > > > > @@ -12,6 +12,7 @@ > > > > */ > > > > > > > > #include "../locking/rtmutex_common.h" > > > > +#include > > > > > > > > static bool rcu_rdp_is_offloaded(struct rcu_data *rdp) > > > > { > > > > @@ -1065,13 +1066,20 @@ static int rcu_boost(struct rcu_node *rnp) > > > > * section. > > > > */ > > > > t = container_of(tb, struct task_struct, rcu_node_entry); > > > > + if (!rnp->exp_tasks && (dl_task(t) || t->prio <= current->prio)) { > > > > + tb = rcu_next_node_entry(t, rnp); > > > > + WRITE_ONCE(rnp->boost_tasks, tb); > > > > + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > > > > + goto end; > > > > + } > > > > + > Why do you bypass the expedited grace period and boost any tasks anyway? > Same way the expedited gp can be blocked by higher prior tasks SCHED_DEADLINE > or SCHED_FIFO. Just to make sure that I understand... Are you pointing out that a SCHED_DEADLINE task might have exhausted its budget, so that boosting might nonetheless be helpful? Me, I honestly don't know what happens in that case, so I am just asking the question. And adding Juri on CC. ;-) Thanx, Paul