Re: [RFC PATCH v2 0/4] tracing/osnoise: Track IPIs

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 17 Jun 2026 15:17:55 +0200
Valentin Schneider <vschneid@redhat.com> wrote:

> Hi folks,
> 
> So I've seen a few times now reports of latency spikes caused by IPIs, usually
> because of isolation misconfiguration, but only detected at the tail of end
> e.g. a 24h timerlat run.
> 
> It's not because those IPIs are rare, but rather that they don't by themselves
> cause a monitered CPU to reach the latency threshold, it's usually a combined
> interference that gets us there.
> 
> I'd like to make it easier to detect such misconfigurations and thus IPIs
> hitting supposedly-isolated CPUs. I initially kludged a timerlat option to stop
> tracing as soon as an IPI was sent to a monitored CPU, regardless of the latency
> threshold. It sort of did the trick, but Tomáš convinced me timerlat wasn't
> really the place for that.
> 
> So here's IPI tracking added to osnoise. This time around fully in userspace, as
> Tomáš pointed out to me that this will make it a lot easier to deploy to older
> kernels.
> 
> Based on top of linux/next at 'next-20260616' to have the latest libsubcmd
> changes.
>   

Hi Valentin,

My new job actually makes me very interested in IPI interference, and
this patch set looks *very* interesting. I'm currently finishing up my
orientation and hopefully next week I can start catching up on all my
email.

I'll try to take a deeper look at this in the coming weeks.

-- Steve