On 2026-01-09 17:18, Alexei Starovoitov wrote:
On Fri, Jan 9, 2026 at 2:00 PM Steven Rostedt <[email protected]> wrote:
On Fri, 9 Jan 2026 13:54:34 -0800
Alexei Starovoitov <[email protected]> wrote:
On Fri, Jan 9, 2026 at 12:21 PM Mathieu Desnoyers
<[email protected]> wrote:
* preempt disable/enable pair: 1.1 ns
* srcu-fast lock/unlock: 1.5 ns
CONFIG_RCU_REF_SCALE_TEST=y
* migrate disable/enable pair: 3.0 ns
.. and you're arguing that 3ns vs 1ns difference is so important
for your out-of-tree tracer that in-tree tracers need to do
some workarounds?! wtf
This has nothing to do with out of tree tracers. The overhead of the
22ns is for any tracepoint in an in-tree module. That's because the
rq->nr_pinned isn't exported for modules to use.
None of the driver's tracepoints are in the critical path.
You perfectly know that Mathieu argued about not slowing down lttng.
My argument is about not slowing down high-throughput tracers
on preempt-rt kernels. This affects ftrace as well as lttng,
so both in-tree and OOT tracers just alike.
Are you so sure that no tracepoint instrumentation whatsoever can
be compiled into a module which is a critical path for some workload ?
That's a bold statement.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
