From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754031AbdIYVGx (ORCPT ); Mon, 25 Sep 2017 17:06:53 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:46295 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753950AbdIYVGw (ORCPT ); Mon, 25 Sep 2017 17:06:52 -0400 Date: Mon, 25 Sep 2017 23:06:39 +0200 (CEST) From: Thomas Gleixner To: Paul Burton cc: Ralf Baechle , dianders@chromium.org, James Hogan , Brian Norris , Jason Cooper , jeffy.chen@rock-chips.com, Marc Zyngier , linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, tfiga@chromium.org Subject: Re: [RFC PATCH v1 2/9] genirq: Support shared per_cpu_devid interrupts In-Reply-To: <20170907232542.20589-3-paul.burton@imgtec.com> Message-ID: References: <1682867.tATABVWsV9@np-p-burton> <20170907232542.20589-1-paul.burton@imgtec.com> <20170907232542.20589-3-paul.burton@imgtec.com> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) 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 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 7 Sep 2017, Paul Burton wrote: > Up until now per_cpu_devid interrupts have not supported sharing. On > MIPS we have some percpu interrupts which are shared in many systems - > a single CPU interrupt line may be used to indicate a timer interrupt, > performance counter interrupt or fast debug channel interrupt. We have > up until now supported this with a series of hacks, wherein drivers call > each other's interrupt handlers & our MIPS GIC irqchip driver includes a > hack which configures the interrupt(s) for all CPUs. In order to allow > this mess to be cleaned up, this patch introduces support for shared > per_cpu_devid interrupts. > > The major portion of this is supporting per_cpu_devid interrupts in > __handle_irq_event_percpu() and then making use of this, via > handle_irq_event_percpu(), from handler_percpu_devif_irq() to invoke the > handler for all actions associated with the shared interrupt. This does > have a few side effects worth noting: > > - per_cpu_devid interrupts will now add to the entropy pool via > add_interrupt_randomness(), where they previously did not. > > - per_cpu_devid interrupts will record timings when IRQS_TIMINGS is > set, via record_irq_time(), where they previously did not. > > - per_cpu_devid interrupts will handle an IRQ_WAKE_THREAD return from > their handlers to wake a thread, where they previously did not. That's broken because it lacks the magic synchronization which is described in the comment in __irq_wake_thread(). > I'm not aware of any reason the above should be bad side effects, so > sharing __handle_irq_event_percpu() for per_cpu_devid interrupts seems > like a positive. Now you are :) The other side effect of this is the extra overhead. You add an extra conditional into the main interrupt handling function __handle_irq_event_percpu() and the extra loop and hoops overhead for handle_percpu_devid_irq(). Thanks, tglx