From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Sent: Tuesday, June 4, 2024 11:14 AM > > Michael! > > On Mon, Jun 03 2024 at 22:09, mhkelley58@xxxxxxxxx wrote: > > Hyper-V VMBus devices generate interrupts that are multiplexed > > onto a single per-CPU architectural interrupt. The top-level VMBus > > driver ISR demultiplexes these interrupts and invokes per-device > > handlers. Currently, these per-device handlers are not modeled as > > Linux IRQs, so /proc/interrupts shows all VMBus interrupts as accounted > > to the top level architectural interrupt. Visibility into per-device > > interrupt stats requires accessing VMBus-specific entries in sysfs. > > The top-level VMBus driver ISR also handles management-related > > interrupts that are not attributable to a particular VMBus device. > > > > As part of changing VMBus to model VMBus per-device handlers as > > normal Linux IRQs, the top-level VMBus driver needs to conditionally > > account for interrupts. If it passes the interrupt off to a > > device-specific IRQ, the interrupt stats are done by that IRQ > > handler, and accounting for the interrupt at the top level > > is duplicative. But if it handles a management-related interrupt > > itself, then it should account for the interrupt itself. > > > > Introduce a new flow handler that provides this functionality. > > The new handler parallels handle_percpu_irq(), but does stats > > only if the ISR returns other than IRQ_NONE. The existing > > handle_untracked_irq() can't be used because it doesn't work for > > per-cpu IRQs, and it doesn't provide conditional stats. > > There is a two other options to solve this: > Thanks for taking a look. Unfortunately, unless I'm missing something, both options you suggest have downsides. > 1) Move the inner workings of handle_percpu_irq() out into > a static function which returns the 'handled' value and > share it between the two handler functions. The "inner workings" aren't quite the same in the two cases. handle_percpu_irq() uses handle_irq_event_percpu() while handle_percpu_demux_irq() uses __handle_irq_event_percpu(). The latter doesn't do add_interrupt_randomness() because the demultiplexed IRQ handler will do it. Doing add_interrupt_randomness() twice doesn't break anything, but it's more overhead in the hard irq path, which I'm trying to avoid. The extra functionality in the non-double-underscore version could be hoisted up to handle_percpu_irq(), but that offsets gains from sharing the inner workings. > > 2) Allocate a proper interrupt for the management mode and invoke it > via generic_handle_irq() just as any other demultiplex interrupt. > That spares all the special casing in the core code and just > works. Yes, this would work on x86, as the top-level interrupt isn't a Linux IRQ, and the interrupt counting is done in Hyper-V specific code that could be removed. The demux'ed interrupt does the counting. But on arm64 the top-level interrupt *is* a Linux IRQ, so each interrupt will get double-counted, which is a problem. Having to add handle_percpu_demux_irq() to handle arm64 correctly isn't as clean as I wish it could be. But I couldn't find a better approach. Michael
