From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933075AbXH3SiQ (ORCPT ); Thu, 30 Aug 2007 14:38:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932403AbXH3SiB (ORCPT ); Thu, 30 Aug 2007 14:38:01 -0400 Received: from tomts5-srv.bellnexxia.net ([209.226.175.25]:40100 "EHLO tomts5-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758156AbXH3SiA (ORCPT ); Thu, 30 Aug 2007 14:38:00 -0400 Date: Thu, 30 Aug 2007 14:37:58 -0400 From: Mathieu Desnoyers To: Christoph Hellwig , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Jens Axboe Subject: Re: [patch 4/4] Port of blktrace to the Linux Kernel Markers. Message-ID: <20070830183758.GB15657@Krystal> References: <20070827160540.007809201@polymtl.ca> <20070827160710.807499112@polymtl.ca> <20070830172128.GA14460@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <20070830172128.GA14460@infradead.org> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 14:35:58 up 31 days, 18:54, 7 users, load average: 0.32, 0.31, 0.33 User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Christoph Hellwig (hch@infradead.org) wrote: > On Mon, Aug 27, 2007 at 12:05:44PM -0400, Mathieu Desnoyers wrote: > > Here is the first stage of a port of blktrace to the Linux Kernel Markers. The > > advantage of this port is that it minimizes the impact on the running when > > blktrace is not active. > > > > A few remarks : this patch has the positive effect of removing some code > > from the block io tracing hot paths, minimizing the i-cache impact in a > > system where the io tracing is compiled in but inactive. > > > > It also moves the blk tracing code from a header (and therefore from the > > body of the instrumented functions) to a separate C file. > > > > There, as soon as one device has to be traced, all devices have to > > execute the tracing function call when they pass by the instrumentation site. > > This is slower than the previous inline function which tested the condition > > quickly. > > > > It does not make the code smaller, since I left all the specialized > > tracing functions for requests, bio, generic, remap, which would go away > > once a generic infrastructure is in place to serialize the information > > passed to the marker. This is mostly why I consider it as a step towards the > > full improvements that could bring the markers. > > I like this as it moves the whole tracing code out of line. It would > be nice if we could make blktrace a module with this, but we'd need > to change the interface away from an ioctl on the block device for that. > > Btw, something that really shows here and what I noticed in my sputrace > aswell is that there is a lot of boilerplate code due to the varargs > trace handlers. We really need some way to auto-generate the boilerplate > for the trace function to avoid coding this up everywhere. Or we can use a vprintk-like function to parse the format string and serialize the information into trace buffers. I prefer this latter option because, overall, it will localize the probes in a few bytes of functions instead of duplicating the memory and instruction cache required by multiple serializing functions. I have the code ready, but I do not want to flood LKML with patches neither.... Mathieu -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68