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 X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8860EC2D0A3 for ; Thu, 29 Oct 2020 09:15:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E249D206F7 for ; Thu, 29 Oct 2020 09:15:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="zl2TnM+b" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726004AbgJ2JPs (ORCPT ); Thu, 29 Oct 2020 05:15:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44528 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725823AbgJ2JPr (ORCPT ); Thu, 29 Oct 2020 05:15:47 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 25E6DC0613D2 for ; Thu, 29 Oct 2020 02:15:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=HPE0ACEf6W8DQ5FCmdGG8czPfeEBhPvB2gnXlAsfIN0=; b=zl2TnM+bFwrXMMfByOij8+J3jr u3SMLV7iROfgKOBljVRI8NkZ+XwFFbAg8KYGQBkQZoFI1yGPIONdzhWcdCdu3MvPgskxDmDr7IHTB FatIGysZNRLLw5cz6iPTVm34H6LkWWUmr+NMZjqeIDj5CcsRqYZ1ga5+bIskJwiCbBXJrINdf5iCE WknJR91gpSFjAfUYvYmkPaVFyzMKg7ASA3uKWHJENmNTftu4Ryjrts0fCs4lZyHdpcEU1B7ZL9RlJ gtdzZVth8x8s3nxMd1/NA/8Q/408rbMV2sWFvV+PPhXvUxp0A2Z3XyGtqlhNMveIQ9tfqpTejOyCY JvdX8mog==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kY41v-0005ZW-Kv; Thu, 29 Oct 2020 09:15:35 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 48CB03006D0; Thu, 29 Oct 2020 10:15:34 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 365A82BECFBBC; Thu, 29 Oct 2020 10:15:34 +0100 (CET) Date: Thu, 29 Oct 2020 10:15:34 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, will@kernel.org, hch@lst.de, axboe@kernel.dk, chris@chris-wilson.co.uk, davem@davemloft.net, kuba@kernel.org, fweisbec@gmail.com, oleg@redhat.com, vincent.guittot@linaro.org Subject: Re: [RFC][PATCH v3 6/6] rcu/tree: Use irq_work_queue_remote() Message-ID: <20201029091534.GH2628@hirez.programming.kicks-ass.net> References: <20201028110707.971887448@infradead.org> <20201028111221.584884062@infradead.org> <20201028145428.GE2628@hirez.programming.kicks-ass.net> <20201028200243.GJ2651@hirez.programming.kicks-ass.net> <20201028201554.GE3249@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201028201554.GE3249@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 28, 2020 at 01:15:54PM -0700, Paul E. McKenney wrote: > On Wed, Oct 28, 2020 at 09:02:43PM +0100, Peter Zijlstra wrote: > > -#ifdef CONFIG_IRQ_WORK > > + raw_spin_lock_rcu_node(rnp); > > The caller of rcu_implicit_dynticks_qs() already holds this lock. > Please see the force_qs_rnp() function and its second call site, > to which rcu_implicit_dynticks_qs() is passed as an argument. Like this then. --- Subject: rcu/tree: Use irq_work_queue_remote() From: Peter Zijlstra Date: Wed Oct 28 11:53:40 CET 2020 The effect of an self-IPI here would be setting rcu_iw_gp_seq to the value we just set it to (pointless) and clearing rcu_iw_pending, which we just set, so don't set it. Signed-off-by: Peter Zijlstra (Intel) --- kernel/rcu/tree.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1204,6 +1204,8 @@ static int rcu_implicit_dynticks_qs(stru bool *ruqp; struct rcu_node *rnp = rdp->mynode; + raw_lockdep_assert_held_rcu_node(rnp); + /* * If the CPU passed through or entered a dynticks idle phase with * no active irq/NMI handlers, then we can safely pretend that the CPU @@ -1308,14 +1310,14 @@ static int rcu_implicit_dynticks_qs(stru resched_cpu(rdp->cpu); WRITE_ONCE(rdp->last_fqs_resched, jiffies); } -#ifdef CONFIG_IRQ_WORK if (!rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq && (rnp->ffmask & rdp->grpmask)) { - rdp->rcu_iw_pending = true; rdp->rcu_iw_gp_seq = rnp->gp_seq; - irq_work_queue_on(&rdp->rcu_iw, rdp->cpu); + if (likely(rdp->cpu != smp_processor_id())) { + rdp->rcu_iw_pending = true; + irq_work_queue_remote(rdp->cpu, &rdp->rcu_iw); + } } -#endif } return 0;