Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756897AbZCJRGr (ORCPT ); Tue, 10 Mar 2009 13:06:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753955AbZCJRGi (ORCPT ); Tue, 10 Mar 2009 13:06:38 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:54153 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752971AbZCJRGi (ORCPT ); Tue, 10 Mar 2009 13:06:38 -0400 Date: Tue, 10 Mar 2009 18:06:07 +0100 From: Ingo Molnar To: Alan Stern Cc: prasad@linux.vnet.ibm.com, Andrew Morton , Linux Kernel Mailing List , Roland McGrath Subject: Re: [patch 04/11] Introduce virtual debug register in thread_struct and wrapper-routines around process related functions Message-ID: <20090310170607.GB22897@elte.hu> References: <20090310143543.GE3850@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1654 Lines: 44 * Alan Stern wrote: > On Tue, 10 Mar 2009, Ingo Molnar wrote: > > > and why is this: > > > > > @@ -427,13 +427,9 @@ struct thread_struct { > > > unsigned long ip; > > > unsigned long fs; > > > unsigned long gs; > > > - /* Hardware debugging registers: */ > > > - unsigned long debugreg0; > > > - unsigned long debugreg1; > > > - unsigned long debugreg2; > > > - unsigned long debugreg3; > > > - unsigned long debugreg6; > > > - unsigned long debugreg7; > > > + /* Hardware breakpoint info */ > > > + unsigned long vdr6; > > > + struct thread_hw_breakpoint *hw_breakpoint_info; > > > > detached from thread_struct? There's a lot of complications > > (alloc/free, locking, etc.) from this for no good reason - the > > hardware-breakpoints info structure is alway per thread and is > > quite small, so there's no reason not to embedd it directly > > inside thread_struct. > > The only reason for separating it out was to avoid bogging > down the vast majority of threads which aren't debugged. If > you think the extra overhead isn't worth worrying about then > the hw-breakpoint info structure can be embedded. yeah. This new facility is barely used, and such things should always strive for 100% dumb simplicity. If the overhead of that structure is ever a problem we can allocate it dynamically. (but generally it's just not worth the pain) Ingo -- 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/