From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 80424C6778C for ; Thu, 5 Jul 2018 16:59:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 408FB23E80 for ; Thu, 5 Jul 2018 16:59:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 408FB23E80 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754528AbeGEQ7s (ORCPT ); Thu, 5 Jul 2018 12:59:48 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:51188 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754109AbeGEQ7r (ORCPT ); Thu, 5 Jul 2018 12:59:47 -0400 Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1fb7bV-0008Bz-IK; Thu, 05 Jul 2018 18:59:37 +0200 Date: Thu, 5 Jul 2018 18:59:37 +0200 From: Sebastian Andrzej Siewior To: Joe Korty Cc: Julia Cartwright , tglx@linutronix.de, rostedt@goodmis.org, linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra Subject: Re: [PATCH RT] sched/migrate_disable: fallback to preempt_disable() instead barrier() Message-ID: <20180705165937.5orx3md3krg4akaz@linutronix.de> References: <20180704173519.GA24614@zipoli.concurrent-rt.com> <20180705155034.s6q2lsqc3o7srzwp@linutronix.de> <20180705161807.GA5800@zipoli.concurrent-rt.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180705161807.GA5800@zipoli.concurrent-rt.com> User-Agent: NeoMutt/20180512 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018-07-05 12:18:07 [-0400], joe.korty@concurrent-rt.com wrote: > Hi Sebastian, Hi Joe, > I just verified that this fix does not work for my mix of > config options (smp && preempt && !rt). Okay. So for !RT+SMP we keep migrate_disable() around and it almost nothing. And it is not referenced anywhere so it does not matter as long as it not used directly. We could turn migrate_disable() into a nop/barrier but then we have three uses which do preempt_disable() -> migrate_disable() (see other thread). For the futex code it should not matter much because at this point preemption is disabled due to the spin_lock() (so we would just extend it past the spin_unlock() or wake_futex_pi() which ends with preempt_enable()). > Regards, > Joe Sebastian