From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [PATCH v4 12/20] genirq: Document vcpu_info usage for percpu_devid interrupts Date: Fri, 20 Oct 2017 13:56:16 +0200 (CEST) Message-ID: References: <20171020114939.12554-1-christoffer.dall@linaro.org> <20171020114939.12554-13-christoffer.dall@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: <20171020114939.12554-13-christoffer.dall@linaro.org> Sender: kvm-owner@vger.kernel.org To: Christoffer Dall Cc: kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, Marc Zyngier , Shih-Wei Li , Christoffer Dall List-Id: kvmarm@lists.cs.columbia.edu On Fri, 20 Oct 2017, Christoffer Dall wrote: Please Cc lkml when changing genirq core code. > It is currently unclear how to set the VCPU affinity for a percpu_devid > interrupt , since the Linux irq_data structure describes the state for > multiple interrupts, one for each physical CPU on the system. Since > each such interrupt can be associated with different VCPUs or none at > all, associating a single VCPU state with such an interrupt does not > capture the necessary semantics. > > The implementers of irq_set_affinity are the Intel and AMD IOMMUs, and > the ARM GIC irqchip. The Intel and AMD callers do not appear to use > percpu_devid interrupts, and the ARM GIC implementation only checks the > pointer against NULL vs. non-NULL. > > Therefore, simply update the function documentation to explain the > expected use in the context of percpu_devid interrupts, allowing future > changes or additions to irqchip implementers to do the right thing. > > This allows us to set the VCPU affinity for the virtual timer interrupt > in KVM/ARM, which is a percpu_devid (PPI) interrupt. I have a hard time to understand how adding the comment allows you to set VCPU affinity .... Thanks, tglx