From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II Date: Mon, 18 Feb 2008 15:41:13 -0500 Message-ID: <20080218204112.GA22031@Krystal> References: <20071231060911.GB6461@in.ibm.com> <20080103163055.GB27651@Krystal> <20080104105858.GA13865@in.ibm.com> <20080105124632.GA16576@Krystal> <20080107195038.GA5119@in.ibm.com> <47B97E63.3070205@siemens.com> <20080218194825.GF10471@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Jan Kiszka , prasad@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, mingo@elte.hu, Gautham R Shenoy , linux-rt-users@vger.kernel.org, dipankar@in.ibm.com To: "Paul E. McKenney" Return-path: Received: from tomts43.bellnexxia.net ([209.226.175.110]:53438 "EHLO tomts43-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752333AbYBRUlQ (ORCPT ); Mon, 18 Feb 2008 15:41:16 -0500 Content-Disposition: inline In-Reply-To: <20080218194825.GF10471@linux.vnet.ibm.com> Sender: linux-rt-users-owner@vger.kernel.org List-ID: * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > On Mon, Feb 18, 2008 at 01:47:31PM +0100, Jan Kiszka wrote: > > K. Prasad wrote: > > > Hi Ingo, > > > Please accept these patches into the rt tree which convert the > > > existing RCU tracing mechanism for Preempt RCU and RCU Boost into > > > markers. > > > > > > These patches are based upon the 2.6.24-rc5-rt1 kernel tree. > > > > > > Along with marker transition, the RCU Tracing infrastructure has also > > > been modularised to be built as a kernel module, thereby enabling > > > runtime changes to the RCU Tracing infrastructure. > > > > > > Patch [1/2] - Patch that converts the Preempt RCU tracing in > > > rcupreempt.c into markers. > > > > > > Patch [1/2] - Patch that converts the Preempt RCU Boost tracing in > > > rcupreempt-boost.c into markers. > > > > > > > I have a technical problem with marker-based RCU tracing: It causes > > nasty recursions with latest multi-probe marker patches (sorry, no link > > at hand, can be found in latest LTTng, maybe also already in -mm). Those > > patches introduce a marker probe trampoline like this: > > > > void marker_probe_cb(const struct marker *mdata, void *call_private, > > const char *fmt, ...) > > { > > va_list args; > > char ptype; > > > > /* > > * rcu_read_lock does two things : disabling preemption to make sure the > > * teardown of the callbacks can be done correctly when they are in > > * modules and they insure RCU read coherency. > > */ > > rcu_read_lock(); > > preempt_disable(); > > ... > > > > Can we do multi-probe with pure preempt_disable/enable protection? I > > guess it's fine with classic RCU, but what about preemptible RCU? Any > > suggestion appreciated! > > If you substitute synchronize_sched() for synchronize_rcu(), this should > work fine. Of course, this approach would cause RCU tracing to degrade > latencies somewhat in -rt. > > If tracing is using call_rcu(), we will need to add a call_sched() > or some such. > Yes, I use call_rcu, so I guess a call_sched would be useful here. Mathieu > Thanx, Paul > > > Jan > > > > PS: You will run into this issue if you try to marry latest -rt with > > latest LTTng. Straightforward workaround is to comment-out any RCU > > trace_mark occurrences. > > > > -- > > Siemens AG, Corporate Technology, CT SE 2 > > Corporate Competence Center Embedded Linux -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68