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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 69947C433E0 for ; Thu, 21 May 2020 21:06:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 28466207D3 for ; Thu, 21 May 2020 21:06:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590095172; bh=04b1QXcN35zporxzNipoNmfuohtrbWnj2rPjb21UsbM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=UNyHk5/nH44PUR/3EpVc6gOV3YrLvVJsWFeTv+9HBLCi/LKqa6NGuTsNGnP26+H+a t+PRBWePzTqPUeVbQEXTv9YEQoj7Qhbfo41lnTq/HF87599D5O7hKmDwXj/a9FBLPV gtPe66TeqJPTVQxd3WXm/cKq7HMe69oWJCAKEDRo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730485AbgEUVGL (ORCPT ); Thu, 21 May 2020 17:06:11 -0400 Received: from mail.kernel.org ([198.145.29.99]:50734 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729756AbgEUVGL (ORCPT ); Thu, 21 May 2020 17:06:11 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6C17820759; Thu, 21 May 2020 21:06:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590095170; bh=04b1QXcN35zporxzNipoNmfuohtrbWnj2rPjb21UsbM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=qXqwtbkZxD/SLNRKHnpt+xYa2jrvDtyspW0jriP+MYQrusPT2GgomuCMf7axt3yiT kuAs10QM6yll7CVllwrBtKw0zwNzsuSmV3KTfUHhrsf8aKzrpUGoDYdvZLSKTGyYZf LbA0xAPn7+pR4JaaPcBoTZ1nuw8F6+zNQiVuh2oE= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 515763522FEB; Thu, 21 May 2020 14:06:10 -0700 (PDT) Date: Thu, 21 May 2020 14:06:10 -0700 From: "Paul E. McKenney" To: Thomas Gleixner Cc: LKML , Andy Lutomirski , Andrew Cooper , X86 ML , Alexandre Chartre , Frederic Weisbecker , Paolo Bonzini , Sean Christopherson , Masami Hiramatsu , Petr Mladek , Steven Rostedt , Joel Fernandes , Boris Ostrovsky , Juergen Gross , Brian Gerst , Mathieu Desnoyers , Josh Poimboeuf , Will Deacon , Tom Lendacky , Wei Liu , Michael Kelley , Jason Chen CJ , Zhao Yakui , "Peter Zijlstra (Intel)" Subject: Re: [patch V9 04/39] x86/entry: Provide idtentry_entry/exit_cond_rcu() Message-ID: <20200521210610.GA25708@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200521200513.656533920@linutronix.de> <20200521202117.181397835@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200521202117.181397835@linutronix.de> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 21, 2020 at 10:05:17PM +0200, Thomas Gleixner wrote: > From: Thomas Gleixner > > After a lengthy discussion [1] it turned out that RCU does not need a full > rcu_irq_enter/exit() when RCU is already watching. All it needs if > NOHZ_FULL is active is to check whether the tick needs to be restarted. > > This allows to avoid a separate variant for the pagefault handler which > cannot invoke rcu_irq_enter() on a kernel pagefault which might sleep. > > The cond_rcu argument is only temporary and will be removed once the > existing users of idtentry_enter/exit() have been cleaned up. After that > the code can be significantly simplified. And yes, I see that the sole call to rcu_irq_enter_check_tick() does have instrumentation turned on, so good! ;-) Thanx, Paul