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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DD0FEC61D90 for ; Tue, 21 Nov 2023 16:03:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234877AbjKUQD0 (ORCPT ); Tue, 21 Nov 2023 11:03:26 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34734 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231439AbjKUQDX (ORCPT ); Tue, 21 Nov 2023 11:03:23 -0500 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D1E2C12E; Tue, 21 Nov 2023 08:03:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=xrV8w2QzC0MyzNqKKokweVMq304wzVwsffOY7txoyDw=; b=pxLYa1yvNDM7PJ4z90aSWcYO8I l/UHXMGWJ1cglHpMgDCh0p2U9xJovVfw+drVFc7z2ve2C1zZ5bch4lBgGsmnBo7W1/1boh70Pa/il 72JF7494XgFbRvJ95WfuzljmOM0xu6FPIhGWyxJOzIu1hHHvDv/cAQ7UolXdwBDXip+lzhPgDYrN5 b5dFOOTkQhcDaAlszc2U8MgmrXNLe/w9EVT1OQt+EujAKRMboYeXqeoazUEapaarghC+k6LQAOQf0 oNUqZB933q6t1Bp/q3rnkZCx9CfQD1SKeGTeyAj/1MywbiYJu7ZjqKAE6LbhXwBg200pMewLpmFl6 IfJxLCGg==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1r5TDJ-00BUZT-2S; Tue, 21 Nov 2023 16:03:02 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 64251300338; Tue, 21 Nov 2023 17:03:00 +0100 (CET) Date: Tue, 21 Nov 2023 17:03:00 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: Mathieu Desnoyers , Steven Rostedt , Masami Hiramatsu , linux-kernel@vger.kernel.org, Michael Jeanson , Alexei Starovoitov , Yonghong Song , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , bpf@vger.kernel.org, Joel Fernandes Subject: Re: [PATCH v4 1/5] tracing: Introduce faultable tracepoints Message-ID: <20231121160300.GK8262@noisy.programming.kicks-ass.net> References: <20231120205418.334172-1-mathieu.desnoyers@efficios.com> <20231120205418.334172-2-mathieu.desnoyers@efficios.com> <20231120214742.GC8262@noisy.programming.kicks-ass.net> <62c6e37c-88cc-43f7-ac3f-1c14059277cc@paulmck-laptop> <20231120222311.GE8262@noisy.programming.kicks-ass.net> <20231121084706.GF8262@noisy.programming.kicks-ass.net> <20231121143647.GI8262@noisy.programming.kicks-ass.net> <2a41f6cd-971d-4360-aeeb-a9cbf665bb72@paulmck-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2a41f6cd-971d-4360-aeeb-a9cbf665bb72@paulmck-laptop> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 21, 2023 at 07:58:40AM -0800, Paul E. McKenney wrote: > Tasks Trace RCU allows general blocking in its readers, not just the > subject-to-priority-boosting blocking permitted within preemptible RCU > readers. Restrictions on the use of Tasks Trace RCU are in place to allow > getting away with this general blocking. Even systems generously endowed > with memory are not going to do well when the RCU grace period is blocked > on I/O, especially if that I/O is across a network to a slow file server. > > Which means a separate RCU instance is needed. Which is Tasks Trace RCU. Separate instance not a problem, nor really the question. What is the basic mechanism of task-tracing? Is it really the existing tasks-rcu extended with read-side critical sections and call_rcu ? If so, then why not have it be tasks-rcu? Or is it a variant of the preemptible/SRCU class of RCUs that are counter-array based? I suspect not. So once again, what exactly is tasks-tracing ?