Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751933AbdHGM4Y (ORCPT ); Mon, 7 Aug 2017 08:56:24 -0400 Received: from foss.arm.com ([217.140.101.70]:48396 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751364AbdHGM4X (ORCPT ); Mon, 7 Aug 2017 08:56:23 -0400 Subject: Re: [PATCH v3] irqchip/tango: Don't use incorrect irq_mask_ack callback To: Marc Gonzalez , Florian Fainelli , Doug Berger References: <20170719190734.18566-1-opendmb@gmail.com> <20170719190734.18566-3-opendmb@gmail.com> <7a51555f-8191-9ebd-1f30-7c20f6db9d3f@sigmadesigns.com> <8d29fec9-35b8-c33b-3091-3e9a51c99ed7@gmail.com> <6f0092f7-692f-4a15-1d95-40f4e59c8585@sigmadesigns.com> <3b858e14-0da1-d4aa-eb84-f136ece8c2a6@gmail.com> <48734beb-0e6b-3a8f-ebf4-b1cec63322e5@gmail.com> Cc: Mans Rullgard , Mason , Thomas Gleixner , Jason Cooper , LKML , Linux ARM From: Marc Zyngier Organization: ARM Ltd Message-ID: Date: Mon, 7 Aug 2017 13:56:20 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3359 Lines: 83 On 28/07/17 15:06, Marc Gonzalez wrote: > On 27/07/2017 20:17, Florian Fainelli wrote: > >> On 07/26/2017 12:13 PM, Måns Rullgård wrote: >> >>> Florian Fainelli writes: >>> >>>> On 07/25/2017 06:29 AM, Måns Rullgård wrote: >>>> >>>>> Marc Gonzalez writes: >>>>> >>>>>> On 25/07/2017 15:16, Måns Rullgård wrote: >>>>>> >>>>>>> What happened to the patch adding the proper combined function? >>>>>> >>>>>> It appears you're not CCed on v2. >>>>>> >>>>>> https://patchwork.kernel.org/patch/9859799/ >>>>>> >>>>>> Doug wrote: >>>>>>> Yes, you understand correctly. The irq_mask_ack method is entirely >>>>>>> optional and I assume that is why this issue went undetected for so >>>>>>> long; however, it is slightly more efficient to combine the functions >>>>>>> (even if the ack is unnecessary) which is why I chose to do so for my >>>>>>> changes to the irqchip-brcmstb-l2 driver where I first discovered this >>>>>>> issue. How much value the improved efficiency has is certainly >>>>>>> debatable, but interrupt handling is one area where people might care >>>>>>> about such a small difference. As the irqchip-tango driver maintainer >>>>>>> you are welcome to decide whether or not the irq_mask_ack method makes >>>>>>> sense to you. >>>>>> >>>>>> My preference goes to leaving the irq_mask_ack callback undefined, >>>>>> and let the irqchip framework use irq_mask and irq_ack instead. >>>>> >>>>> Why would you prefer the less efficient way? >>>>> >>>> >>>> Same question here, that does not really make sense to me. >>>> >>>> The whole point of this patch series is to have a set of efficient and >>>> bugfree (or nearly) helper functions that drivers can rely on, are you >>>> saying that somehow using irq_mask_and_ack is exposing a bug in the >>>> tango irqchip driver and using the separate functions does not expose >>>> this bug? >>> >>> There is currently a bug in that the function used doesn't do what its >>> name implies which can't be good. Using the separate mask and ack >>> functions obviously works, but combining them saves a lock/unlock >>> sequence. The correct combined function has already been written, so I >>> see no reason not to use it. >> >> Marc/Mason, are you intending to get this patch accepted in order to >> provide a quick bugfix targeting earlier kernels with the tango irqchip >> driver or is this how you think the correct fix for the tango irqchip >> driver is as opposed to using Doug's fix? > > Hello Florian, > > I am extremely grateful for you and Doug bringing the defect to > my attention, as it was indeed causing an issue which I had not > found the time to investigate. > > The reason I proposed an alternate patch is that > 1) Doug didn't seem to mind, 2) simpler code leads to fewer bugs > and less maintenance IME, and 3) I didn't see many drivers using > the irq_mask_ack() callback (9 out of 86) with a few misusing it, > by defining irq_mask = irq_mask_ack. > > As you point out, my patch might be slightly easier to backport > than Doug's (TBH, I hadn't considered that aspect until you > mentioned it). > > Has anyone ever quantified the performance improvement of > mask_ack over mask + ack? Aren't you the one who is in position of measuring this effect on the actual HW that uses this? Thanks, M. -- Jazz is not dead. It just smells funny...