From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751212AbWGDIWU (ORCPT ); Tue, 4 Jul 2006 04:22:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751217AbWGDIWU (ORCPT ); Tue, 4 Jul 2006 04:22:20 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:3992 "EHLO pentafluge.infradead.org") by vger.kernel.org with ESMTP id S1751212AbWGDIWT (ORCPT ); Tue, 4 Jul 2006 04:22:19 -0400 Subject: Re: [PATCH 1/2] x86-64 TIF flags for debug regs and io bitmap in ctxsw From: Arjan van de Ven To: Andi Kleen Cc: eranian@hpl.hp.com, linux-kernel@vger.kernel.org In-Reply-To: <200607041009.31588.ak@suse.de> References: <20060704072832.GB5902@frankl.hpl.hp.com> <1151999509.3109.6.camel@laptopd505.fenrus.org> <200607041009.31588.ak@suse.de> Content-Type: text/plain Date: Tue, 04 Jul 2006 10:22:16 +0200 Message-Id: <1152001336.3109.10.camel@laptopd505.fenrus.org> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2006-07-04 at 10:09 +0200, Andi Kleen wrote: > On Tuesday 04 July 2006 09:51, 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) ? > > Where do you see an atomic operation? test_tsk_thread_flag() ends up doing an atomic op afaics