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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 E2481C2BA83 for ; Thu, 13 Feb 2020 08:27:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B31A2222C2 for ; Thu, 13 Feb 2020 08:27:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="iRzU+Cyh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729588AbgBMI16 (ORCPT ); Thu, 13 Feb 2020 03:27:58 -0500 Received: from merlin.infradead.org ([205.233.59.134]:37828 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729401AbgBMI15 (ORCPT ); Thu, 13 Feb 2020 03:27:57 -0500 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=hBfDlwtqklEammb2YxFsK0X9jlsEpvDn83y+O10mAko=; b=iRzU+Cyhwkt+b7sSBUwIG5Yb9Y T+kqkDL/I76g1B8E0nsqwBKUHE2vQadqc6LO6nwboFfRhV/fURG2GIHlWiwodWxoppLM8xLq63nR4 vYM+dTP8QWEUPAVdQnIXbX7X9f8H5FjQzh7t6LlYZx4DidQ+Pe+IgKKUZExtlfw0Cpd349Xx1JBo4 y5luIsMUYs25lqboCl04k1imEULFW7tYlO+JFlGi7HkgDmg6bU8ruCcXdrg0n8GozwceNEHUwwld+ h7/FakeGnqrL9bCsLKaXh+8f56/XfCBDojWB4Blv69fs11oJjGXK/5cuR3DE48jNiQRS4evG4wV6A NhT8P+3A==; 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 1j29qA-0005cI-EY; Thu, 13 Feb 2020 08:27:18 +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 39CD63012D8; Thu, 13 Feb 2020 09:25:27 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 8664C20206D6B; Thu, 13 Feb 2020 09:27:16 +0100 (CET) Date: Thu, 13 Feb 2020 09:27:16 +0100 From: Peter Zijlstra To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, rostedt@goodmis.org, mingo@kernel.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, paulmck@kernel.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com Subject: Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}() Message-ID: <20200213082716.GI14897@hirez.programming.kicks-ass.net> References: <20200212210139.382424693@infradead.org> <20200212210749.971717428@infradead.org> <20200212232005.GC115917@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200212232005.GC115917@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 12, 2020 at 06:20:05PM -0500, Joel Fernandes wrote: > On Wed, Feb 12, 2020 at 10:01:42PM +0100, Peter Zijlstra wrote: > > +#define trace_rcu_enter() \ > > +({ \ > > + unsigned long state = 0; \ > > + if (!rcu_is_watching()) { \ > > + if (in_nmi()) { \ > > + state = __TR_NMI; \ > > + rcu_nmi_enter(); \ > > + } else { \ > > + state = __TR_IRQ; \ > > + rcu_irq_enter_irqsave(); \ > > I think this can be simplified. You don't need to rely on in_nmi() here. I > believe for NMI's, you can just call rcu_irq_enter_irqsave() and that should > be sufficient to get RCU watching. Paul can correct me if I'm wrong, but I am > pretty sure that would work. > > In fact, I think a better naming for rcu_irq_enter_irqsave() pair could be > (in the first patch): > > rcu_ensure_watching_begin(); > rcu_ensure_watching_end(); So I hadn't looked deeply into rcu_irq_enter(), it seems to call rcu_nmi_enter_common(), but with @irq=true. What exactly is the purpose of that @irq argument, and how much will it hurt to lie there? Will it come apart if we have @irq != !in_nmi() for example? There is a comment in there that says ->dynticks_nmi_nesting ought to be odd only if we're in NMI. The only place that seems to care is rcu_nmi_exit_common(), and that does indeed do something different for IRQs vs NMIs. So I don't think we can blindly unify this. But perhaps Paul sees a way?