From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Sent: Wednesday, June 5, 2024 6:20 AM > > On Tue, Jun 04 2024 at 23:03, Michael Kelley wrote: > > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Sent: Tuesday, June 4, 2024 11:14 AM > >> 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. > > That's not rocket science to solve: > > static irqreturn_t helper(desc, func) > { > boiler_plate.. > ret = func(desc) > boiler_plate.. > return ret; > } > > No? > > TBH, I still hate that conditional accounting :) > > >> 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. > > What is the problem? > > You have: toplevel, mgmt, device[], right? > > They are all accounted for seperately and each toplevel interrupt might > result in demultiplexing one or more interrupts (mgmt, device[]), no? > > IMO accounting the toplevel interrupt seperately is informative because > it allows you to figure out whether demultiplexing is clustered or not, > but I lost that argument long ago. That's why most demultiplex muck > installs a chained handler, which is a design fail on it's own. In /proc/interrupts, the double-counting isn't a problem, and is potentially helpful as you say. But /proc/stat, for example, shows a total interrupt count, which will be roughly double what it was before. That /proc/stat value then shows up in user space in vmstat, for example. That's what I was concerned about, though it's not a huge problem in the grand scheme of things. Michael