On 26/06/26 06:26, Steven Rostedt wrote:

On Wed, 17 Jun 2026 15:17:55 +0200
Valentin Schneider [off-list ref] wrote:

quoted

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.

Welcome back :-) If IPIs are your thing, you may also have a look at
[1]. I'm working on a v10 following some (surprisingly) useful feedback
from Sashiko.

[1]: https://lore.kernel.org/lkml/20260505082355.1982003-1-vschneid@redhat.com/ (local)

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

Thanks!

-- Steve