Re: [PATCH 4/4] ARCv2: entry: Reduce perf intr return path

[Vineet Gupta]

On 11/17/2017 03:42 PM, Vineet Gupta wrote:

> > > > What do you (on ARC) do about irq_work ?
>
> > So the reason I'm asking is that some architectures that don't have NMIs
> > call irq_work_run() at the very end of their perf-interrupt handler (ARM
> > does this for instance).
>
> But on ARC, we don't call irq_work_run() in perf intr return path and that seem to 
> imply it is broken - as in latency to service a perf induced preemption.

[snip...]

> > > Although I'm sure it is, can you please explain how irq_work is relevant in
> > > the context of this patch.
> >
> > Since the perf interrupt (in general) cannot call a whole lot of things
> > for it needs to assume running from NMI context, it needs to defer
> > things to a more regular context. It does this with irq_work.

So given my understanding of this topic, ARC (or any non NMI based perf intr 
system) is potentially broken without irq_work_run() ?

I can follow up with a patch for ARC, or does this need to addressed for others 
too - say irq_exit_perf() or some such ?