From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752930AbbBKPDW (ORCPT ); Wed, 11 Feb 2015 10:03:22 -0500 Received: from down.free-electrons.com ([37.187.137.238]:35889 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751398AbbBKPDU (ORCPT ); Wed, 11 Feb 2015 10:03:20 -0500 Date: Wed, 11 Feb 2015 16:03:17 +0100 From: Boris Brezillon To: "Rafael J. Wysocki" Cc: Mark Rutland , Thomas Gleixner , Jason Cooper , Nicolas Ferre , Jean-Christophe Plagniol-Villard , Alexandre Belloni , Rob Herring , Pawel Moll , Ian Campbell , Kumar Gala , "devicetree@vger.kernel.org" , "Rafael J. Wysocki" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq demuxer chip Message-ID: <20150211160317.6d6c64e5@bbrezillon> In-Reply-To: <2437801.56xPyk3atd@vostro.rjw.lan> References: <1422527620-8308-1-git-send-email-boris.brezillon@free-electrons.com> <2982569.CIWvqghzfx@vostro.rjw.lan> <20150211144345.GL9154@leverpostej> <2437801.56xPyk3atd@vostro.rjw.lan> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.23; 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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 11 Feb 2015 16:17:20 +0100 "Rafael J. Wysocki" wrote: > On Wednesday, February 11, 2015 02:43:45 PM Mark Rutland wrote: > > [...] > > > > > > > > > +static irqreturn_t __handle_irq_event_percpu(unsigned int irq, struct irqaction *action) > > > > > > > +{ > > > > > > > + /* > > > > > > > + * During suspend we must not call potentially unsafe irq handlers. > > > > > > > + * See suspend_suspendable_actions. > > > > > > > + */ > > > > > > > + if (unlikely(action->flags & IRQF_NO_ACTION)) > > > > > > > + return IRQ_NONE; > > > > > > > > > > > > Thomas was trying to avoid any new conditional code in the interrupt > > > > > > handling path, that's why I added a suspended_action list in my > > > > > > proposal. > > > > > > Even if your 'unlikely' statement make things better I'm pretty sure it > > > > > > adds some latency. > > > > > > > > > > I can see that we don't want to add more code here to keep things > > > > > clean/pure, but I find it hard to believe that a single bit test and > > > > > branch (for data that should be hot in the cache) are going to add > > > > > measurable latency to a path that does pointer chasing to get to the > > > > > irqaction in the first place. I could be wrong though, and I'm happy to > > > > > benchmark. > > > > > > > > Again, I don't have enough experience to say this is (or isn't) > > > > impacting irq handling latency, I'm just reporting what Thomas told me. > > > > > > > > > > > > > > It would be possible to go for your list shuffling approach here while > > > > > still keeping the flag internal and all the logic hidden away in > > > > > kernel/irq/pm.c. I wasn't sure how actions could be manipulated during > > > > > suspend, which made me wary of moving them to a separate list. > > > > > > > > Moving them to a temporary list on suspend and restoring them on > > > > resume should not be a problem. > > > > The only drawback I see is that actions might be reordered after the > > > > first resume (anyway, relying on shared irq action order is dangerous > > > > IMHO). > > > > > > We considered doing that too and saw some drawbacks (in addition to the > > > reordering of actions you've mentioned). It added just too much complexity > > > to the IRQ suspend-resume code. > > > > > > I, personally, would be fine with adding an IRQ flag to silence the > > > warning mentioned by Alexandre. Something like IRQD_TIMER_SHARED that would > > > be set automatically if someone requested IRQF_TIMER | IRQF_SHARED. > > > > > > Thoughts? > > > > Even if the timer driver does that, we still require the other handlers > > sharing the line to do the right thing across suspend, no? So either > > their actions need to be masked at suspend time, or the handlers need to > > detect when they're called during suspend and return early. > > Well, the issue at hand is about things that share an IRQ with a timer AFAICS. > > That is odd enough already and I'd say everyone in that situation needs to > be prepared to take the pain (including having to check if the device is not > suspended in their interrupt handlers). > > And quite frankly they need to do that already, because we've never suspended > timer IRQs. > > > So for the flag at request time approach to work, all the drivers using > > the interrupt would have to flag they're safe in that context. > > Something like IRQF_"I can share the line with a timer" I guess? That wouldn't > hurt and can be checked at request time even. > > > I'm not averse to having that (only a few drivers shuold be affected and > > we can sanity check them now). > > Right. Okay, if everyone agrees on this solution, then I'm fine with that too (even if I'm a bit disappointed to have spent so much time on this problem to eventually end-up with a simple IRQF_SHARED_TIMER flag :-(). -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com