From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E8A2518C03D for ; Thu, 10 Oct 2024 10:44:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728557089; cv=none; b=ECK0oNGHnprL0GkdP92xfYrokAoA4jbwA+pe1AsENgvCTC7VrHFar+lacZee0BLuIp9hpZA91U0mDWMcz/rm/IhLtUqGSM+HGuzSfpfm4v/+Izwi1CGiqGZpnDlOkSWGE/fuU+NOX0lAyT1kcl2EUmWQuLvAVSP1rfVOomvhym4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728557089; c=relaxed/simple; bh=HwXtcBfZ9skqTUUIvL6qjtFcMbgAVYIzdtNQEETd01c=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CyteEF/bXvQ8UqfKeAxbi/cXER7ZW1HS7IfkVF2obuY0P3c4tHLZUPUeD6V0nLqYc6A1CkdhCfAP6RhZekfmKPfBABzfzuDrsHMlhtZvLnzqgH2XAuy0Bq0Be1GCcymLY446A8q3jqRP87uyfG9s9gIoqTiWYtexvGw8e87Mka8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=fsqfkYFi; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="fsqfkYFi" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=wt3+UwGS92R+4Ox5ks/fZ0imxBx7Ykqt9KCdpyt4ijs=; b=fsqfkYFi3gwqCB6JIpMC5OY+hp dQ07ZLxCK7nJNO325BO9qC+wrd8Gj754eZB2Pfi5xjt/4B7dOY/AHxaqQT+xcDOPowG/sZ1U0dMVh 5do7dDgErsY7ln6LD3OJSNE9cfWs4D5wdL/upgH3MbCrxjqxk87DlbkCqwrFDpXqcKGfh3Jtf6IAz GtZxlGV8AdFVulLMwEUiJxGapnWaKLW3/JQoC0IggJvc8lvfIg0NogXaCN8B3vnBrXPD5ayVEIO9w HfuSprPUSuYHI0YaZtY7VPlVdcxH/YlspMabBK+Q3YaurgtknePPZ02Vl5YU7610D0p00Ce+txH1W rNlCGeWA==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1syqes-00000005Lbn-3or9; Thu, 10 Oct 2024 10:44:39 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 8A92B30088D; Thu, 10 Oct 2024 12:44:38 +0200 (CEST) Date: Thu, 10 Oct 2024 12:44:38 +0200 From: Peter Zijlstra To: Sebastian Andrzej Siewior Cc: "Paul E. McKenney" , Ankur Arora , linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, frederic@kernel.org, efault@gmx.de Subject: Re: [PATCH 2/7] rcu: limit PREEMPT_RCU configurations Message-ID: <20241010104438.GJ14587@noisy.programming.kicks-ass.net> References: <20241009165411.3426937-1-ankur.a.arora@oracle.com> <20241009165411.3426937-3-ankur.a.arora@oracle.com> <20241009180117.GS17263@noisy.programming.kicks-ass.net> <37af80bd-a54f-4ee4-9175-6f0f27b685a0@paulmck-laptop> <20241010063207.xIrynIqO@linutronix.de> <20241010081032.GA17263@noisy.programming.kicks-ass.net> <20241010091326.nK71dG4b@linutronix.de> <20241010100308.GE17263@noisy.programming.kicks-ass.net> <20241010102657.H7HpIbVp@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20241010102657.H7HpIbVp@linutronix.de> On Thu, Oct 10, 2024 at 12:26:57PM +0200, Sebastian Andrzej Siewior wrote: > On 2024-10-10 12:03:08 [+0200], Peter Zijlstra wrote: > > > > > > I can't deselect CONFIG_PREEMPT_RCU=y. This is because LAZY selects > > > PREEMPT_BUILD and PREEMPT_RCU selects itself once PREEMPTION is on. > > > > Oh, the entry isn't user selectable? Fix that perhaps? > > > > - bool > > + bool "Use preemptible RCU" > > > > Or something along those lines -- I forever forget how Kconfig works. > > Oh. Well, yes. If we do this then it becomes suddenly selectable and > half of the series makes sense… > But as you said, this complicates things. But then you leave it up to the user, instead of doing something quite random. This would allow you to configure PREEMPT_RCU=n despite also using PREEMPT_DYNAMIC if that is your thing. I fundamentally hate the whole randomness of the earlier proposed selection criteria. It only disables PREEMPT_RCU if you use LAZY and not also have PREEMPT_RT or PREEMPT_DYNAMIC.