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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 EEC79C43613 for ; Thu, 20 Jun 2019 21:59:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C20A02075E for ; Thu, 20 Jun 2019 21:59:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726326AbfFTV7t (ORCPT ); Thu, 20 Jun 2019 17:59:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49856 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725906AbfFTV7t (ORCPT ); Thu, 20 Jun 2019 17:59:49 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2B0AFBB00; Thu, 20 Jun 2019 21:59:36 +0000 (UTC) Received: from ovpn-117-83.phx2.redhat.com (ovpn-117-83.phx2.redhat.com [10.3.117.83]) by smtp.corp.redhat.com (Postfix) with ESMTP id E1D1860477; Thu, 20 Jun 2019 21:59:30 +0000 (UTC) Message-ID: Subject: Re: [RFC PATCH RT 3/4] rcu: unlock special: Treat irq and preempt disabled the same From: Scott Wood To: paulmck@linux.ibm.com Cc: Sebastian Andrzej Siewior , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Juri Lelli , Clark Williams , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 20 Jun 2019 16:59:30 -0500 In-Reply-To: <20190620211005.GW26519@linux.ibm.com> References: <20190619011908.25026-1-swood@redhat.com> <20190619011908.25026-4-swood@redhat.com> <20190620211005.GW26519@linux.ibm.com> Organization: Red Hat Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Thu, 20 Jun 2019 21:59:49 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2019-06-20 at 14:10 -0700, Paul E. McKenney wrote: > On Tue, Jun 18, 2019 at 08:19:07PM -0500, Scott Wood wrote: > > [Note: Just before posting this I noticed that the invoke_rcu_core stuff > > is part of the latest RCU pull request, and it has a patch that > > addresses this in a more complicated way that appears to deal with the > > bare irq-disabled sequence as well. > > Far easier to deal with it than to debug the lack of it. ;-) > > > Assuming we need/want to support such sequences, is the > > invoke_rcu_core() call actually going to result in scheduling any > > sooner? resched_curr() just does the same setting of need_resched > > when it's the same cpu. > > ] > > Yes, invoke_rcu_core() can in some cases invoke the scheduler sooner. > Setting the CPU-local bits might not have effect until the next interrupt. Maybe I'm missing something, but I don't see how (in the non-use_softirq case). It just calls wake_up_process(), which in resched_curr() will set need_resched but not do an IPI-to-self. -Scott