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 3CDC1C388F7 for ; Wed, 28 Oct 2020 21:44:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E2FEF2475D for ; Wed, 28 Oct 2020 21:44:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="C3lLiHVQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726548AbgJ1VoB (ORCPT ); Wed, 28 Oct 2020 17:44:01 -0400 Received: from merlin.infradead.org ([205.233.59.134]:59036 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726469AbgJ1Vnx (ORCPT ); Wed, 28 Oct 2020 17:43:53 -0400 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=ABPtItGeR+X+7i3YNqfiZCGYLEmimF/MG0DPydax2M8=; b=C3lLiHVQscuY4AofJPv950mrrQ kwye7LTieNv/TTwVOS5m7pTjfiSXdGrIW1yh6r9SCIX+PugnIL28BRDE3cg+vFI74qrmwHP+YYG35 e3LXnaCN6hhXS9brEXZRTtm7pxGEW/8RfK6RxtTSgALRIOktYoc2PZ2uG4hWF153f0f9IO2avUez6 vtTP9EHAcbx2cErQ32Scu1iEAnzR+lAhSPJc85PJNWnhs3EKaBxqtgLFfZ5bmpU0xc74QTAzCzt+8 ojOffxNVUhMmnriNESNowYBB1Dchp04js1twOwF3PwAIvsyfyHenGf8/My0f+GbvKOPN1sWAJ9IzP ZnHEI0rA==; 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 1kXref-0003iE-IT; Wed, 28 Oct 2020 20:02:45 +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 0042E301179; Wed, 28 Oct 2020 21:02:43 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E05412038A985; Wed, 28 Oct 2020 21:02:43 +0100 (CET) Date: Wed, 28 Oct 2020 21:02:43 +0100 From: Peter Zijlstra To: mingo@kernel.org Cc: linux-kernel@vger.kernel.org, will@kernel.org, paulmck@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: <20201028200243.GJ2651@hirez.programming.kicks-ass.net> References: <20201028110707.971887448@infradead.org> <20201028111221.584884062@infradead.org> <20201028145428.GE2628@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201028145428.GE2628@hirez.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 28, 2020 at 03:54:28PM +0100, Peter Zijlstra wrote: > On Wed, Oct 28, 2020 at 12:07:13PM +0100, Peter Zijlstra wrote: > > AFAICT we only need/use irq_work_queue_on() on remote CPUs, since we > > can directly access local state. So avoid the IRQ_WORK dependency and > > use the unconditionally available irq_work_queue_remote(). > > > > This survives a number of TREE01 runs. > > OK, Paul mentioned on IRC that while it is extremely unlikely, this code > does not indeed guarantee it will not try to IPI self. > > I'll try again. This is the best I could come up with.. :/ --- Subject: rcu/tree: Use irq_work_queue_remote() From: Peter Zijlstra Date: Wed Oct 28 11:53:40 CET 2020 All sites that consume rcu_iw_gp_seq seem to have rcu_node lock held, so setting it probably should too. Also the effect of 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. Passes TREE01. 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 @@ -1308,14 +1308,16 @@ static int rcu_implicit_dynticks_qs(stru resched_cpu(rdp->cpu); WRITE_ONCE(rdp->last_fqs_resched, jiffies); } -#ifdef CONFIG_IRQ_WORK + raw_spin_lock_rcu_node(rnp); 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 + raw_spin_unlock_rcu_node(rnp); } return 0;