Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755402Ab3IIQkr (ORCPT ); Mon, 9 Sep 2013 12:40:47 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:26954 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754466Ab3IIQkq (ORCPT ); Mon, 9 Sep 2013 12:40:46 -0400 X-Authority-Analysis: v=2.0 cv=fJG7LOme c=1 sm=0 a=Sro2XwOs0tJUSHxCKfOySw==:17 a=Drc5e87SC40A:10 a=JDfofD-L5ZgA:10 a=5SG0PmZfjMsA:10 a=kj9zAlcOel0A:10 a=meVymXHHAAAA:8 a=KGjhK52YXX0A:10 a=5p3hctMY2UsA:10 a=VnNF1IyMAAAA:8 a=mlFgsZHGq9pVYmy25QwA:9 a=CjuIK1q_8ugA:10 a=4bZfTmQAmYoA:10 a=Sro2XwOs0tJUSHxCKfOySw==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 67.255.60.225 Date: Mon, 9 Sep 2013 12:40:44 -0400 From: Steven Rostedt To: paulmck@linux.vnet.ibm.com Cc: Peter Zijlstra , Frederic Weisbecker , Eric Dumazet , linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, sbw@mit.edu Subject: Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical section? Message-ID: <20130909124044.2e851d97@gandalf.local.home> In-Reply-To: <20130909162215.GY3966@linux.vnet.ibm.com> References: <20130906174117.GU3966@linux.vnet.ibm.com> <20130906185927.GE2706@somewhere> <20130909105347.GK31370@twins.programming.kicks-ass.net> <20130909121329.GA16280@somewhere> <20130909083926.3eceebef@gandalf.local.home> <20130909124547.GB16280@somewhere> <20130909085504.2ddd7e69@gandalf.local.home> <20130909131452.GA31370@twins.programming.kicks-ass.net> <20130909134605.GP3966@linux.vnet.ibm.com> <20130909095511.735bcffc@gandalf.local.home> <20130909162215.GY3966@linux.vnet.ibm.com> X-Mailer: Claws Mail 3.9.2 (GTK+ 2.24.20; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1156 Lines: 28 On Mon, 9 Sep 2013 09:22:15 -0700 "Paul E. McKenney" wrote: > However, the API we are arguing about is deep within the implementation. > It is not at the level of rcu_read_lock(). It is something that should > not have that many invocations -- after all, the things using it are > binding themselves unusually close to RCU. > Is it? I guess the question is, is dynamic ticks an extension of RCU, or is it just using the RCU implementation as a convenience? Also the OP patch is for function tracing, something not coupled by RCU at all. Just a way to know if it is safe to call functions that use RCU or not. That can have "this_cpu()" by the way as a way to tell us that we must disable preemption before hand. Which is what caused this thread to start with, as it was suggested to combine rcu_is_cpu_idle() which brought up why that function disables preemption. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/