From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756114AbbJAIN0 (ORCPT ); Thu, 1 Oct 2015 04:13:26 -0400 Received: from www.linutronix.de ([62.245.132.108]:55933 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755568AbbJAINS (ORCPT ); Thu, 1 Oct 2015 04:13:18 -0400 Date: Thu, 1 Oct 2015 10:12:23 +0200 (CEST) From: Thomas Gleixner To: Andy Lutomirski cc: Chris Metcalf , Gilad Ben Yossef , Steven Rostedt , Ingo Molnar , Peter Zijlstra , Andrew Morton , Rik van Riel , Tejun Heo , Frederic Weisbecker , "Paul E. McKenney" , Christoph Lameter , Viresh Kumar , Catalin Marinas , Will Deacon , "linux-kernel@vger.kernel.org" , "H. Peter Anvin" , X86 ML Subject: Re: [PATCH v7 07/11] arch/x86: enable task isolation functionality In-Reply-To: Message-ID: References: <1443453446-7827-1-git-send-email-cmetcalf@ezchip.com> <1443453446-7827-8-git-send-email-cmetcalf@ezchip.com> <5609B7C0.3010807@ezchip.com> <560ACD6F.7060102@ezchip.com> <560C4CF4.9090601@ezchip.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001,URIBL_BLOCKED=0.001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 30 Sep 2015, Andy Lutomirski wrote: > On Wed, Sep 30, 2015 at 3:02 PM, Thomas Gleixner wrote: > > On Wed, 30 Sep 2015, Chris Metcalf wrote: > >> So for now, if a task-isolation thread sets up a timer, > >> they're screwed: so, don't do that. And it's really not part of > >> the typical programming model for these kinds of userspace > >> drivers anyway, so it's pretty reasonable to forbid it. > > > > There is a difference between forbidding it and looping for 10 minutes > > in the kernel. > > I don't even like forbidding it. Setting timers seems like an > entirely reasonable thing for even highly RT or isolated programs to > do, although admittedly they can do it on a non-RT thread and then > kick the RT thread when they're ready. > > Heck, even without the TSC deadline timer, the kernel could, in > principle, support that use case by having whatever core is doing > housekeeping keep kicking the can forward until it's time to IPI the > isolated core because it needs to wake up. That's simple. Just arm the timer on the other core. It's not rocket science to do that. But the whole problem with this isolation stuff is, that it tries to push half baken duct tape concepts into the tree. That would be the same if we'd brute force merge the RT stuff and then let everyone deal with the fallout. There is a really good reason, why the remaining - hard to solve - pieces of RT are still out of tree. And I really want to see a proper engineering for that isolation stuff, which can be done with an out of tree patch set in the first place. But sure, it's more convenient to push crap into mainline and let everyone else deal with the fallouts. Thanks, tglx