From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756984AbaHHQkX (ORCPT ); Fri, 8 Aug 2014 12:40:23 -0400 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.229]:33003 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752646AbaHHQkW (ORCPT ); Fri, 8 Aug 2014 12:40:22 -0400 Date: Fri, 8 Aug 2014 12:40:18 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: "Paul E. McKenney" , Oleg Nesterov , linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, bobby.prani@gmail.com, masami.hiramatsu.pt@hitachi.com Subject: Re: [PATCH v3 tip/core/rcu 3/9] rcu: Add synchronous grace-period waiting for RCU-tasks Message-ID: <20140808124018.46724b50@gandalf.local.home> In-Reply-To: <20140808161709.GF9918@twins.programming.kicks-ass.net> References: <20140807154907.6f59cf6e@gandalf.local.home> <20140807155326.18481e66@gandalf.local.home> <20140807200813.GB3935@laptop> <20140807171823.1a481290@gandalf.local.home> <20140808064020.GZ9918@twins.programming.kicks-ass.net> <20140808101221.21056900@gandalf.local.home> <20140808143413.GB9918@twins.programming.kicks-ass.net> <20140808105858.171da847@gandalf.local.home> <20140808151643.GD9918@twins.programming.kicks-ass.net> <20140808113949.046522c5@gandalf.local.home> <20140808161709.GF9918@twins.programming.kicks-ass.net> X-Mailer: Claws Mail 3.10.1 (GTK+ 2.24.24; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.118:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 8 Aug 2014 18:17:09 +0200 Peter Zijlstra wrote: > On Fri, Aug 08, 2014 at 11:39:49AM -0400, Steven Rostedt wrote: > > Also, anyone can register a function handler (perf, systemtap, and even > > LTTng can). > > So how common is it to have more than 1 function event handler, and how > many of those cases is there significant difference in the actual > functions? For me, it's quite common. Of course, I tend to poweruse function tracing :-). I do make instances and trace a few functions here and there, while tracing all functions. Note, if you are tracing all functions, all it takes is just adding one other ops callback to a single function. That is, if you are tracing all functions, and add another ops, it will make all users use the list function. That is. Even though only one function has two callbacks attached to it, all functions will call the list function, which does make a noticeable difference. I measured it once before, I'll have to do it again. Tracing all functions is extremely invasive, and any increase in the time of the function callback handlers will have a dramatic hit on performance. An mcount nop, causes 13% slowdown. Imagine what adding a loop does. > > Because that's the case you're optimizing for. Why is that an important > enough case. > > I'm thinking I'll never trigger that, I only ever have the one normal > ftrace handler. So no trampolines for me, the code you have now works > just fine. > And it will work just fine afterward :-) I will treat any regressions as a significant (high priority) bug. -- Steve