Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933324AbbLHP5K (ORCPT ); Tue, 8 Dec 2015 10:57:10 -0500 Received: from mail-wm0-f49.google.com ([74.125.82.49]:33370 "EHLO mail-wm0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932665AbbLHP5I (ORCPT ); Tue, 8 Dec 2015 10:57:08 -0500 Date: Tue, 8 Dec 2015 16:57:05 +0100 From: Frederic Weisbecker To: Peter Zijlstra Cc: LKML , Chris Metcalf , Thomas Gleixner , Luiz Capitulino , Christoph Lameter , Ingo Molnar , Viresh Kumar , Rik van Riel Subject: Re: [PATCH 2/7] nohz: New tick dependency mask Message-ID: <20151208155703.GA4192@lerouge> References: <1447424529-13671-1-git-send-email-fweisbec@gmail.com> <1447424529-13671-3-git-send-email-fweisbec@gmail.com> <20151201204109.GN17308@twins.programming.kicks-ass.net> <20151201222025.GA31973@lerouge> <20151202105633.GQ3816@twins.programming.kicks-ass.net> <20151202140815.GB14766@lerouge> <20151202150908.GR3816@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151202150908.GR3816@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2249 Lines: 55 On Wed, Dec 02, 2015 at 04:09:08PM +0100, Peter Zijlstra wrote: > On Wed, Dec 02, 2015 at 03:08:16PM +0100, Frederic Weisbecker wrote: > > On Wed, Dec 02, 2015 at 11:56:33AM +0100, Peter Zijlstra wrote: > > > On Tue, Dec 01, 2015 at 11:20:28PM +0100, Frederic Weisbecker wrote: > > > > > > + prev = fetch_or(dep, BIT_MASK(bit)); > > > > > > + if (!prev) { > > > > > > + /* > > > > > > + * We need the IPIs to be sent from sane process context. > > > > > > > > > > Why ? > > > > > > > > Because posix timers code is all called with interrupts disabled and we can't > > > > send IPIs then. > > > > > > > > > > > > > > > + * The posix cpu timers are always set with irqs disabled. > > > > > > + */ > > > > > > + schedule_work(&kick_all_work); > > > > > > + } > > > > > > +} > > > > > > + > > > > > > +/* > > > > > > + * Set a global tick dependency. Lets do the wide IPI kick asynchronously > > > > > > + * for callers with irqs disabled. > > > > > > > > > > This seems to suggest you can call this with IRQs disabled > > > > > > > > Ah right, that's a misleading comment. We need to use the _delayed() version > > > > when interrupts are disabled. > > > > > > Why can't you use tick_nohz_full_kick_cpu() for all that, which is > > > usable from IRQ context and avoid all that delayed muck? > > > > Because I need to kick all the CPUs where the task/signal is running on. That's > > a bit difficult to do though. I think we had something to try to send an IPI to a task, > > but I can't retrieve it. Looks easy to do anyway. But in the signal case I'd need to do > > that for all tasks in the group. That sounds like a costly loop. > > > > So I simplify that with a global IPI. > > Sure, but what I meant was that: > > for_each_cpu(cpu, mask) > tick_nohz_full_kick_cpu(cpu); > > is IRQ safe, whereas the current thingy is not. Sure, its a wee bit less > efficient, but do we really care? Right, this overhead probably doesn't matter much. I'll do that and we'll see if people complain. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/