Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761019AbYGOCw2 (ORCPT ); Mon, 14 Jul 2008 22:52:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754669AbYGOCwS (ORCPT ); Mon, 14 Jul 2008 22:52:18 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:44294 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754198AbYGOCwR (ORCPT ); Mon, 14 Jul 2008 22:52:17 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Steven Rostedt Cc: Andrew Morton , Randy Dunlap , Elias Oltmanns , LKML , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Clark Williams , Linus Torvalds , Jon Masters References: <87zlop7bp6.fsf@denkblock.local> <20080710132832.38cc5048.randy.dunlap@oracle.com> <20080711121655.05810822.akpm@linux-foundation.org> <20080711153740.b86acadd.akpm@linux-foundation.org> Date: Mon, 14 Jul 2008 19:41:47 -0700 In-Reply-To: (Steven Rostedt's message of "Mon, 14 Jul 2008 22:18:09 -0400 (EDT)") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-SA-Exim-Connect-IP: 24.130.11.59 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa01 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Steven Rostedt X-Spam-Relay-Country: X-Spam-Report: * -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -0.2 BAYES_40 BODY: Bayesian spam probability is 20 to 40% * [score: 0.2339] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa01 1397; Body=1 Fuz1=1 Fuz2=1] * 0.5 XM_Body_Dirty_Words Contains a dirty word * 0.0 XM_SPF_Neutral SPF-Neutral Subject: Re: [PATCH -v2] ftrace: Documentation X-SA-Exim-Version: 4.2 (built Thu, 03 Mar 2005 10:44:12 +0100) X-SA-Exim-Scanned: Yes (on mgr1.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2118 Lines: 52 Steven Rostedt writes: >> Ok. So this is something simpler to use then SystemTap. Yeah. > > Yes, very similar. SystemTap may even hook into ftrace, and vice versa. Got it. >> It sounds like it is reasonable or at least semi reasonable to use >> this as an unprivileged user. > > Currently only root can do the traces. Since some of the tracing can > hurt the performance of the system. Reasonable. >> The easiest model to think of this in is a chroot that does pids as >> well as the filesystem. In which case if you are inside one and >> you use the tracer. You want pids that are meaningful in your >> subset of userspace, and not the global ones. > > Some tracers do a trace at every function call. This uses the gcc -pg > option to set up the start of each function to call profiling code. > Dynamic ftrace is a on the fly code modification to maintain good > performance while tracing is disabled. > > Because of this being such a high critical path, can I get the namespace > pid information directly from the task structure. Any function that is > called must also be careful to not fall back into the tracer. The trace > deals with self recursion, but functions that call back to the tracer > cause a bigger performance impact while tracing. All of the interesting functions are inline so it shouldn't be a big deal. Mostly they exist to keep the semantics clear as we refactor the code. task_pid_nr(tsk) yields the global pid number, and is currently implemented as just tsk->pid. task_pid(tsk) yields the struct pid. task_pid_nr_ns(tsk) yields the pid number from the perspective of a specific task. struct pid is interesting because it is immune from pid roll over conflicts. I don't know if that is any use to you or not. stuct pid contains an embedded array of the pid_nrs one for each namespace the struct pid is in. Eric -- 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/