From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sun, 9 Mar 2003 12:04:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sun, 9 Mar 2003 12:04:36 -0500 Received: from dbl.q-ag.de ([80.146.160.66]:12254 "EHLO dbl.q-ag.de") by vger.kernel.org with ESMTP id ; Sun, 9 Mar 2003 12:04:35 -0500 Message-ID: <3E6B769D.2040602@colorfullife.com> Date: Sun, 09 Mar 2003 18:15:09 +0100 From: Manfred Spraul User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2) Gecko/20021202 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andi Kleen CC: linux-kernel@vger.kernel.org Subject: Re: [PATCH] Fast path context switch - microoptimize FPU reload Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andi wrote: >We don't need the lock prefix to test our local thread flags state. >Unfortunately test_thread_flag currently always uses test_bit which >has a LOCK on SMP, but that's unnecessary. LOCK is costly on P4, >so it's a good idea to avoid it. > > No, LOCK is required: the TIF_ flags word is also used for signal delivery - writing without lock could corrupt state. What about moving TIF_USEDFPU from the thread_info into task_struct->flags? This flag word is only accessed by "current", no special atomicity requirements. -- Manfred