On 2025-07-17 12:02, Alexei Starovoitov wrote:

On Thu, Jul 17, 2025 at 8:55 AM Steven Rostedt [off-list ref] wrote:

quoted

On Thu, 17 Jul 2025 11:40:28 -0400
Steven Rostedt [off-list ref] wrote:

quoted

Yes, it is a tracepoint infra problem that we are trying to solve. The
reason we are trying to solve it is because BPF programs can extend the
time a tracepoint takes. If anything else extended the time, this would
need to be solved as well. But currently it's only BPF programs that
cause the issue.

BTW, if we can't solve this issue and something else came along and
attached to tracepoints that caused unbounded latency, I would also
argue that whatever came along would need to be prevented from being
configured with PREEMPT_RT. My comment wasn't a strike against BPF
programs; It was a strike against something adding unbounded latency
into a critical section that has preemption disabled.

Stop blaming the users. Tracepoints disable preemption for now
good reason and you keep shifting the blame.
Fix tracepoint infra.

I think we're all agreeing here that it's the tracepoint instrumentation
infrastructure that needs to be changed to become more RT friendly, and
that BPF is merely the tracepoint user that happens to have the longest
running callbacks at the moment.

So AFAIU there is no blame on BPF here, and no expectation for any
changes in BPF neither.

Thanks,

Mathieu



-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com