Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 9 Jul 2002 22:19:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 9 Jul 2002 22:19:34 -0400 Received: from serenity.mcc.ac.uk ([130.88.200.93]:57362 "EHLO serenity.mcc.ac.uk") by vger.kernel.org with ESMTP id ; Tue, 9 Jul 2002 22:19:33 -0400 Date: Wed, 10 Jul 2002 03:22:08 +0100 From: John Levon To: Karim Yaghmour Cc: Linus Torvalds , Andrew Morton , Andrea Arcangeli , Rik van Riel , "linux-mm@kvack.org" , "Martin J. Bligh" , linux-kernel@vger.kernel.org, Richard Moore , bob Subject: Re: Enhanced profiling support (was Re: vm lock contention reduction) Message-ID: <20020710022208.GA56823@compsoc.man.ac.uk> References: <3D29DCBC.5ADB7BE8@opersys.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3D29DCBC.5ADB7BE8@opersys.com> User-Agent: Mutt/1.3.25i X-Url: http://www.movementarian.org/ X-Record: Boards of Canada - Geogaddi Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1750 Lines: 42 On Mon, Jul 08, 2002 at 02:41:00PM -0400, Karim Yaghmour wrote: > dentry + offset: on a 32bit machine, this is 8 bytes total per event being > profiled. This is a lot of information if you are trying you have a high > volume throughput. I haven't found that to be significant in profiling overhead, mainly because the hash table removes some of the "sting" of high sampling rates (and the interrupt handler dwarfs all other aspects). The situation is probably different for more general tracing purposes, but I'm dubious as to the utility of a general tracing mechanism. (besides, a profile buffer needs a sample context value too, for things like CPU number and perfctr event number). > You can almost always skip the dentry since you know scheduling > changes and since you can catch a system-state snapshot at the begining of > the profiling. After that, the eip is sufficient and can easily be correlated > to a meaningfull entry in a file in user-space. But as I point out in my other post, dentry-offset alone is not as useful as it could be... I just don't see a really good reason to introduce insidious tracing throughout. Both tracing and profiling are ugly ugly things to be doing by their very nature, and I'd much prefer to keep such intrusions to a bare minimum. The entry.S examine-the-registers approach is simple enough, but it's not much more tasteful than sys_call_table hackery IMHO regards john -- "I know I believe in nothing but it is my nothing" - Manic Street Preachers - 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/