From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932204AbWGDKXG (ORCPT ); Tue, 4 Jul 2006 06:23:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751261AbWGDKXG (ORCPT ); Tue, 4 Jul 2006 06:23:06 -0400 Received: from ns.suse.de ([195.135.220.2]:61395 "EHLO mx1.suse.de") by vger.kernel.org with ESMTP id S1751259AbWGDKXF (ORCPT ); Tue, 4 Jul 2006 06:23:05 -0400 From: Andi Kleen To: Mikael Pettersson Subject: Re: [PATCH 1/2] x86-64 TIF flags for debug regs and io bitmap in ctxsw Date: Tue, 4 Jul 2006 12:22:42 +0200 User-Agent: KMail/1.9.3 Cc: arjan@infradead.org, eranian@hpl.hp.com, linux-kernel@vger.kernel.org References: <200607040905.k6495M2l028360@harpo.it.uu.se> In-Reply-To: <200607040905.k6495M2l028360@harpo.it.uu.se> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200607041222.42288.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday 04 July 2006 11:05, Mikael Pettersson wrote: > On Tue, 4 Jul 2006 01:14:13 -0700, Stephane Eranian wrote: > >On Tue, Jul 04, 2006 at 09:51:49AM +0200, Arjan van de Ven wrote: > >> > - } > >> > - } > >> > + if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW)) > >> > + || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) > >> > + __switch_to_xtra(prev_p, next_p, tss); > >> > >> well isn't this replacing an if() (which isn't cheap but also not > >> expensive, due to unlikely()) with an atomic operation (which *is* > >> expensive) ? > >> > >Andi is right. I double checked the test_tsk_thread_flag() and it does not > >use atomic ops. > > The test_tsk_thread_flag() does not, but what about all the > other places in the patch where currently unsychronised loads > or stores of ->io_bitmap_ptr or ->debugreg7 get replaced or > extended with locked-on-SMP {set,clear}_{tsk_,}thread_flag() > operations? They are all slow paths where it doesn't matter. -Andi