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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no 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 2A887C7618F for ; Fri, 26 Jul 2019 21:30:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EF9E622BEF for ; Fri, 26 Jul 2019 21:30:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387513AbfGZVa4 (ORCPT ); Fri, 26 Jul 2019 17:30:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:55968 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727398AbfGZVa4 (ORCPT ); Fri, 26 Jul 2019 17:30:56 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B2208217D9; Fri, 26 Jul 2019 21:30:54 +0000 (UTC) Date: Fri, 26 Jul 2019 17:30:52 -0400 From: Steven Rostedt To: Julia Cartwright Cc: Thomas Gleixner , LKML , "x86@kernel.org" , Sebastian Siewior , Anna-Maria Gleixner , Arnaldo Carvalho de Melo , Jiri Olsa , Paolo Bonzini , Juergen Gross Subject: Re: [patch 10/12] hrtimer: Determine hard/soft expiry mode for hrtimer sleepers on RT Message-ID: <20190726173052.66942a7b@gandalf.local.home> In-Reply-To: <20190726211623.GP29109@jcartwri.amer.corp.natinst.com> References: <20190726183048.982726647@linutronix.de> <20190726185753.645792403@linutronix.de> <20190726211623.GP29109@jcartwri.amer.corp.natinst.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 26 Jul 2019 21:16:24 +0000 Julia Cartwright wrote: > > + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { > > + if (task_is_realtime(current) && !(mode & HRTIMER_MODE_SOFT)) > > + mode |= HRTIMER_MODE_HARD; > > Because this ends up sampling the tasks' scheduling parameters only at > the time of enqueue, it doesn't take into consideration whether or not > the task maybe holding a PI lock and later be boosted if contended by an > RT thread. > > Am I correct in assuming there is an induced inversion here in this > case, because the deferred wakeup mechanism isn't part of the PI chain? > > If so, is this just to be an accepted limitation at this point? Is the > intent to argue this away as bad RT application design? :) > Well, it shouldn't be holding any kernel PI locks (aka spin_lock) when it sleeps, but may be holding a PI futex. In which case, I would say is a bad RT application, to have a thread sleep on a non RT timer while holding a lock that an RT Task might take. -- Steve