From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161223AbWGIXkI (ORCPT ); Sun, 9 Jul 2006 19:40:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161224AbWGIXkH (ORCPT ); Sun, 9 Jul 2006 19:40:07 -0400 Received: from liaag2ae.mx.compuserve.com ([149.174.40.156]:56752 "EHLO liaag2ae.mx.compuserve.com") by vger.kernel.org with ESMTP id S1161223AbWGIXkG (ORCPT ); Sun, 9 Jul 2006 19:40:06 -0400 Date: Sun, 9 Jul 2006 19:34:04 -0400 From: Chuck Ebbert <76306.1226@compuserve.com> Subject: Re: [patch] i386: use thread_info flags for debug regs and IO bitmaps To: Linus Torvalds , Stephane Eranian Cc: linux-kernel , Andi Kleen , Andrew Morton Message-ID: <200607091936_MC3-1-C489-B862@compuserve.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org In-Reply-To: On Sat, 8 Jul 2006 14:26:53 -0700, Linus Torvalds wrote: > > On Fri, 7 Jul 2006, Chuck Ebbert wrote: > > > > From: Stephane Eranian > > > > Use thread info flags to track use of debug registers and IO bitmaps. > > > > - add TIF_DEBUG to track when debug registers are active > > - add TIF_IO_BITMAP to track when I/O bitmap is used > > - modify __switch_to() to use the new TIF flags > > Can you explain what the advantages of this are? Stephane's perfmon2 patch adds yet another special-case to the switch_to() code, so Andi suggested this change. It will allow the perfmon2 patch to have no performance impact on normal task-switching, since it will just use another flag. After I saw a ~7% gain in task-switch performance, I like it now even without perfmon2 in there. > I don't see it. It's just creating new state to describe state that we > already had, and as far as I can tell, it's just a way to potentially have > more new bugs thanks to the new state getting out of sync with the old > one? Well yeah, there is that. But Andi and I both reviewed it and he's already put the x86_64 version into his tree. Testing in -mm should show whether there are any problems. -- Chuck "You can't read a newspaper if you can't read." --George W. Bush