From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Sent: Thursday, June 6, 2024 2:34 AM > > On Thu, Jun 06 2024 at 03:14, Michael Kelley wrote: > > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Sent: Wednesday, June 5, 2024 7:20 AM > >> > >> On Wed, Jun 05 2024 at 13:45, Michael Kelley wrote: > >> > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Sent: Wednesday, June 5, 2024 6:20 AM > >> > > >> > 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. > >> > >> That's trivial to solve. We can mark interrupts to be excluded from > >> /proc/stat accounting. > >> > > > > OK. On x86, some simple #ifdef'ery in arch_irq_stat_cpu() can filter > > out the HYP interrupts. But what do you envision on arm64, where > > there is no arch_irq_stat_cpu()? On arm64, the top-level interrupt is a > > normal Linux IRQ, and its count is included in the "kstat.irqs_sum" field > > with no breakout by IRQ. Identifying the right IRQ and subtracting it > > out later looks a lot uglier than the conditional stats accounting. > > Sure. There are two ways to solve that: > > 1) Introduce a IRQ_NO_PER_CPU_STATS flag, mark the interrupt > accordingly and make the stats increment conditional on it. > The downside is that the conditional affects every interrupt. > > 2) Do something like this: > > static inline > void __handle_percpu_irq(struct irq_desc *desc, irqreturn_t (*handle)(struct irq_desc > *)) > { > struct irq_chip *chip = irq_desc_get_chip(desc); > > if (chip->irq_ack) > chip->irq_ack(&desc->irq_data); > > handle(desc); > > if (chip->irq_eoi) > chip->irq_eoi(&desc->irq_data); > } > > void handle_percpu_irq(struct irq_desc *desc) > { > /* > * PER CPU interrupts are not serialized. Do not touch > * desc->tot_count. > */ > __kstat_incr_irqs_this_cpu(desc); > __handle_percpu_irq(desc, handle_irq_event_percpu); > } > > void handle_percpu_irq_nostat(struct irq_desc *desc) > { > __this_cpu_inc(desc->kstat_irqs->cnt); > __handle_percpu_irq(desc, __handle_irq_event_percpu); > } > > So that keeps the interrupt accounted for in /proc/interrupts. If you > don't want that remove the __this_cpu_inc() and mark the interrupt with > irq_set_status_flags(irq, IRQ_HIDDEN). That will exclude it from > /proc/interrupts too. > Yes, this works for not double-counting in the first place. Account for the control message interrupts in their own Linux IRQ. Then for the top-level interrupt, instead of adding a new handler with conditional accounting, add a new per-CPU handler that does no accounting. I had not noticed the IRQ_HIDDEN flag, and that solves my concern about having an entry in /proc/interrupts that always shows zero interrupts. And with no double-counting, the interrupt counts in /proc/stat won't be bloated. On x86, I'll have to separately make the "HYP" line in /proc/interrupts go away, but that's easy. Thanks, Michael