Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism

From: Keith Busch
Date: Fri Sep 06 2019 - 15:01:16 EST

On Fri, Sep 06, 2019 at 11:30:57AM -0700, Sagi Grimberg wrote:
> >
> > Ok, so the real problem is per-cpu bounded tasks.
> >
> > I share Thomas opinion about a NAPI like approach.
> We already have that, its irq_poll, but it seems that for this
> use-case, we get lower performance for some reason. I'm not
> entirely sure why that is, maybe its because we need to mask interrupts
> because we don't have an "arm" register in nvme like network devices
> have?

For MSI, that's the INTMS/INTMC NVMe registers. MSI-x, though, has to
disarm it in its table entry, and the Linux implementation will do a
posted read in that path, which is a bit too expensive.