From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758830AbYJILyT (ORCPT ); Thu, 9 Oct 2008 07:54:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754736AbYJILyK (ORCPT ); Thu, 9 Oct 2008 07:54:10 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:59074 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754319AbYJILyJ (ORCPT ); Thu, 9 Oct 2008 07:54:09 -0400 Date: Thu, 9 Oct 2008 04:54:07 -0700 From: "Paul E. McKenney" To: =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, rjw@sisk.pl, dipankar@in.ibm.com, tglx@linuxtronix.de, andi@firstfloor.org Subject: Re: [PATCH] rudimentary tracing for Classic RCU Message-ID: <20081009115407.GD6628@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20081006232837.GA1157@basil.nowhere.org> <20081007030822.GC6820@linux.vnet.ibm.com> <20081007071544.GC20740@one.firstfloor.org> <20081007152629.GH6384@linux.vnet.ibm.com> <20081007154939.GN20740@one.firstfloor.org> <20081007163401.GJ6384@linux.vnet.ibm.com> <20081007210947.GP20740@one.firstfloor.org> <20081007212215.GN6384@linux.vnet.ibm.com> <20081009010846.GA10188@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 09, 2008 at 12:23:13PM +0200, Frédéric Weisbecker wrote: > 2008/10/9 Paul E. McKenney : > > Hello! > > > > This is a tracing patch for Classic RCU, which creates an "rcu/rcucb" > > file in debugfs. This patch can be handy when you need to work out > > why RCU is refusing to end the current grace period. > > > > Reading from the file results in something like the following: > > > > rcu: cur=1129 completed=1128 np=0 s=0 > > 0,3,7 > > rcu_bh: cur=-287 completed=-287 np=0 s=0 > > > > online: 0-7 > > > Hi Paul, > > Why don't you use the ring-buffer tracing engine? > You will really make your life better by putting it as a tracer in > kernel/trace and by using the relevant API. > That will avoid you to manage the debugfs things, the memory > allocation, the buffer managment..... Hello, Frédéric, Well, one reason is that I didn't know about it. ;-) Does it allow the user to trigger a one-shot trace? Right now, what one does is: cat /debug/rcu/rcucb whenever one wants to see what RCU is up to. You really don't want to see every new value, as that would generate hundreds of trace records per second -- per CPU. What does the user do with the ring-buffer tracing enging? Thanx, Paul