From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH 0/2] Markers Implementation for RCU Tracing - Ver II Date: Mon, 18 Feb 2008 13:47:31 +0100 Message-ID: <47B97E63.3070205@siemens.com> References: <20071231060911.GB6461@in.ibm.com> <20080103163055.GB27651@Krystal> <20080104105858.GA13865@in.ibm.com> <20080105124632.GA16576@Krystal> <20080107195038.GA5119@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, Gautham R Shenoy , mathieu.desnoyers@polymtl.ca, linux-rt-users@vger.kernel.org, dipankar@in.ibm.com, paulmck@linux.vnet.ibm.com To: prasad@linux.vnet.ibm.com Return-path: Received: from gecko.sbs.de ([194.138.37.40]:23724 "EHLO gecko.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755956AbYBRMs2 (ORCPT ); Mon, 18 Feb 2008 07:48:28 -0500 In-Reply-To: <20080107195038.GA5119@in.ibm.com> Sender: linux-rt-users-owner@vger.kernel.org List-ID: 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! 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