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 90A5DC3DA78 for ; Tue, 17 Jan 2023 14:03:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229586AbjAQODO (ORCPT ); Tue, 17 Jan 2023 09:03:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58640 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229830AbjAQODJ (ORCPT ); Tue, 17 Jan 2023 09:03:09 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AE0F538B78; Tue, 17 Jan 2023 06:03:08 -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 5C143B8163C; Tue, 17 Jan 2023 14:03:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9463AC433D2; Tue, 17 Jan 2023 14:03:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1673964185; bh=009ZkaKNNYtdbuuDx1qA9wZr22kzjPWN7yIb2q0DdEA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Dktz/WYJgv4QvyvDV2LbvZmxjtWZWLprYGVoku3jmdDH79C6Rr5ME968EUSWwVcih 5aouenxh36cnXsIEEFum2DRiZ7fyRn287tGrUNutJWRRQ9eRLncilq/HkQXZU5sozk 8LVH6IgiWeLZgkrL7aYIXc530jWklLqfNIt+Ic1JMHjSrXVsqoZ7oFOFwzvsYZ8Hb4 w9nXQds86zFR3FsxlHzM0KN0ABftoBpbKaEfnsnLlY4dXA4e6Zt4junWySb0wHm9nL PPm5Gg7QZWrH9fxX7gsLBKdVJk/MWjV9FiUWvahoFRggZnIrjvjjyj5yJP5IzIB6dZ Ai7kQS9PV+BNA== Date: Tue, 17 Jan 2023 15:03:03 +0100 From: Frederic Weisbecker To: Zqiang Cc: paulmck@kernel.org, quic_neeraju@quicinc.com, joel@joelfernandes.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] rcu: Remove impossible wakeup rcu GP kthread action from rcu_report_qs_rdp() Message-ID: References: <20230117074443.1982347-1-qiang1.zhang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230117074443.1982347-1-qiang1.zhang@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 17, 2023 at 03:44:43PM +0800, Zqiang wrote: > When inovke rcu_report_qs_rdp(), if current CPU's rcu_data structure's -> > grpmask has not been cleared from the corresponding rcu_node structure's > ->qsmask, after that will clear and report quiescent state, but in this > time, this also means that current grace period is not end, the current > grace period is ongoing, because the rcu_gp_in_progress() currently return > true, so for non-offloaded rdp, invoke rcu_accelerate_cbs() is impossible > to return true. > > This commit therefore remove impossible rcu_gp_kthread_wake() calling. > > Signed-off-by: Zqiang > --- > kernel/rcu/tree.c | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index b2c204529478..c78d48482583 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1956,7 +1956,6 @@ rcu_report_qs_rdp(struct rcu_data *rdp) > { > unsigned long flags; > unsigned long mask; > - bool needwake = false; > bool needacc = false; > struct rcu_node *rnp; > > @@ -1988,7 +1987,7 @@ rcu_report_qs_rdp(struct rcu_data *rdp) > * NOCB kthreads have their own way to deal with that... > */ > if (!rcu_rdp_is_offloaded(rdp)) { > - needwake = rcu_accelerate_cbs(rnp, rdp); > + WARN_ON_ONCE(rcu_accelerate_cbs(rnp, rdp)); Please also add a comment explaining why we don't expect to have to wake up the GP kthread. Reviewed-by: Frederic Weisbecker Thanks! > } else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) { > /* > * ...but NOCB kthreads may miss or delay callbacks acceleration > @@ -2000,8 +1999,6 @@ rcu_report_qs_rdp(struct rcu_data *rdp) > rcu_disable_urgency_upon_qs(rdp); > rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); > /* ^^^ Released rnp->lock */ > - if (needwake) > - rcu_gp_kthread_wake(); > > if (needacc) { > rcu_nocb_lock_irqsave(rdp, flags); > -- > 2.25.1 >