Re: [PATCH v2] sched/rt: Have RT_PUSH_IPI be default off for non PREEMPT_RT

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 15 May 2026 08:47:49 -1000
Tejun Heo <tj@kernel.org> wrote:

> Hello, Steven.
> 
> On Fri, May 15, 2026 at 02:38:47PM -0400, Steven Rostedt wrote:
> > Hmm, but I'm guessing that it still was long enough to slow down the
> > softirq to trigger it again and prevent scheduling?  
> 
> Yes, seems that way. I think the load is lower and each softirq invocation
> is relatively short (just going through the packets received in the
> meantime) but the frequency is higher.

I just want to make sure that my analysis is correct. Since only one CPU
can initiate the RT_PUSH_IPI. That for this to be a problem, other CPUs
need to be constantly running RT tasks for short periods of time so that
when the RT task schedules off the CPU, the CPU then initiates the "pull".
And it's not that it happens all at once. It's more serialized where the RT
tasks are scheduling off at different times to constantly feed the
RT_PUSH_IPI logic without seeing that it's already in place.

It would require this to happen enough times to keep the overloaded CPU
from finishing the softirq until a time when the softirq is scheduled
again. And it would maintain this abuse for long enough to trigger the
watchdog.

Does that fit the scenario of your environment?

-- Steve