RE: [RFC 06/12] genirq: Add per-cpu flow handler with conditional IRQ stats

[Michael Kelley]

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.

Or if there's some other approach I'm missing, please enlighten me!

Michael