From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753957AbdHUNZ3 convert rfc822-to-8bit (ORCPT ); Mon, 21 Aug 2017 09:25:29 -0400 Received: from us-smtp-delivery-107.mimecast.com ([216.205.24.107]:21917 "EHLO us-smtp-delivery-107.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753566AbdHUNZ1 (ORCPT ); Mon, 21 Aug 2017 09:25:27 -0400 Subject: Re: [PATCH v3] irqchip/tango: Don't use incorrect irq_mask_ack callback To: Marc Zyngier , Florian Fainelli , Doug Berger CC: Mans Rullgard , Mason , Thomas Gleixner , Jason Cooper , LKML , Linux ARM 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> From: Marc Gonzalez Message-ID: Date: Mon, 21 Aug 2017 15:25:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0 SeaMonkey/2.49.1 MIME-Version: 1.0 In-Reply-To: X-Originating-IP: [172.27.0.114] X-MC-Unique: uekFEeztPC2hhS1H_Upy2A-1 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 On 07/08/2017 14:56, Marc Zyngier wrote: > 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? Using separate mask and ack functions (i.e. my patch) # iperf3 -c 172.27.64.110 -t 20 Connecting to host 172.27.64.110, port 5201 [ 4] local 172.27.64.1 port 40868 connected to 172.27.64.110 port 5201 [ ID] Interval Transfer Bandwidth Retr Cwnd [ 4] 0.00-1.00 sec 106 MBytes 888 Mbits/sec 18 324 KBytes [ 4] 1.00-2.00 sec 106 MBytes 885 Mbits/sec 0 361 KBytes [ 4] 2.00-3.00 sec 105 MBytes 883 Mbits/sec 4 279 KBytes [ 4] 3.00-4.00 sec 106 MBytes 890 Mbits/sec 0 300 KBytes [ 4] 4.00-5.00 sec 106 MBytes 887 Mbits/sec 0 310 KBytes [ 4] 5.00-6.00 sec 105 MBytes 883 Mbits/sec 0 315 KBytes [ 4] 6.00-7.00 sec 105 MBytes 885 Mbits/sec 0 321 KBytes [ 4] 7.00-8.00 sec 105 MBytes 880 Mbits/sec 0 325 KBytes [ 4] 8.00-9.00 sec 106 MBytes 888 Mbits/sec 0 329 KBytes [ 4] 9.00-10.00 sec 106 MBytes 886 Mbits/sec 0 335 KBytes [ 4] 10.00-11.00 sec 105 MBytes 885 Mbits/sec 0 351 KBytes [ 4] 11.00-12.00 sec 106 MBytes 887 Mbits/sec 1 276 KBytes [ 4] 12.00-13.00 sec 106 MBytes 885 Mbits/sec 0 321 KBytes [ 4] 13.00-14.00 sec 105 MBytes 883 Mbits/sec 0 349 KBytes [ 4] 14.00-15.00 sec 106 MBytes 890 Mbits/sec 0 366 KBytes [ 4] 15.00-16.00 sec 106 MBytes 888 Mbits/sec 2 286 KBytes [ 4] 16.00-17.00 sec 105 MBytes 884 Mbits/sec 0 303 KBytes [ 4] 17.00-18.00 sec 105 MBytes 883 Mbits/sec 0 311 KBytes [ 4] 18.00-19.00 sec 105 MBytes 880 Mbits/sec 0 315 KBytes [ 4] 19.00-20.00 sec 106 MBytes 890 Mbits/sec 0 321 KBytes - - - - - - - - - - - - - - - - - - - - - - - - - [ ID] Interval Transfer Bandwidth Retr [ 4] 0.00-20.00 sec 2.06 GBytes 885 Mbits/sec 25 sender Using combined mask and ack functions (i.e. Doug's patch) # iperf3 -c 172.27.64.110 -t 20 Connecting to host 172.27.64.110, port 5201 [ 4] local 172.27.64.1 port 41235 connected to 172.27.64.110 port 5201 [ ID] Interval Transfer Bandwidth Retr Cwnd [ 4] 0.00-1.00 sec 107 MBytes 897 Mbits/sec 60 324 KBytes [ 4] 1.00-2.00 sec 107 MBytes 898 Mbits/sec 0 361 KBytes [ 4] 2.00-3.00 sec 107 MBytes 898 Mbits/sec 39 194 KBytes [ 4] 3.00-4.00 sec 107 MBytes 895 Mbits/sec 0 214 KBytes [ 4] 4.00-5.00 sec 107 MBytes 901 Mbits/sec 0 223 KBytes [ 4] 5.00-6.00 sec 108 MBytes 902 Mbits/sec 0 230 KBytes [ 4] 6.00-7.00 sec 107 MBytes 895 Mbits/sec 0 242 KBytes [ 4] 7.00-8.00 sec 107 MBytes 901 Mbits/sec 0 253 KBytes [ 4] 8.00-9.00 sec 107 MBytes 899 Mbits/sec 0 264 KBytes [ 4] 9.00-10.00 sec 108 MBytes 903 Mbits/sec 0 276 KBytes [ 4] 10.00-11.00 sec 108 MBytes 902 Mbits/sec 0 286 KBytes [ 4] 11.00-12.00 sec 107 MBytes 899 Mbits/sec 0 300 KBytes [ 4] 12.00-13.00 sec 107 MBytes 898 Mbits/sec 33 247 KBytes [ 4] 13.00-14.00 sec 107 MBytes 900 Mbits/sec 0 294 KBytes [ 4] 14.00-15.00 sec 107 MBytes 900 Mbits/sec 0 325 KBytes [ 4] 15.00-16.00 sec 107 MBytes 899 Mbits/sec 0 342 KBytes [ 4] 16.00-17.00 sec 107 MBytes 898 Mbits/sec 0 351 KBytes [ 4] 17.00-18.00 sec 108 MBytes 902 Mbits/sec 0 355 KBytes [ 4] 18.00-19.00 sec 107 MBytes 901 Mbits/sec 0 359 KBytes [ 4] 19.00-20.00 sec 108 MBytes 903 Mbits/sec 32 255 KBytes - - - - - - - - - - - - - - - - - - - - - - - - - [ ID] Interval Transfer Bandwidth Retr [ 4] 0.00-20.00 sec 2.09 GBytes 900 Mbits/sec 164 sender Ergo, it seems that the performance improvement of the combined implementation is approximately 1.5% for a load generating ~80k interrupts per second. I suppose a 1.5% improvement for free should not be ignored. Therefore, I rescind my v3 patch. Doug/Florian, thanks again for fixing the tango driver. Regards.