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

[Valentin Schneider]

On 26/06/26 06:26, Steven Rostedt wrote:
> On Wed, 17 Jun 2026 15:17:55 +0200
> Valentin Schneider <vschneid@xxxxxxxxxx> 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.
>

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@xxxxxxxxxx/

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

Thanks!

> -- Steve