[PATCH v3 0/6] tracing/osnoise: Track IPIs

[Valentin Schneider <vschneid@redhat.com>]

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-20260710' to have the latest libsubcmd
changes. 
  
Cheers,
Valentin

Revisions
=========

v2 -> v3
++++++++

o Dropped the short-form -i option to leave it free 
o Re-arranged top header printing 
o Fixed tracefs_event_file_write() return value handling

o Changed IPI filtering to allow it to gracefully fail on older kernels
o Added filter clearing for -e events to ensure a known state


v1 -> v2
++++++++

o Dropped the in-kernel osnoise_sample changes and made it all userspace

Valentin Schneider (6):
  rtla/osnoise: Add IPI tracking cmdline option
  rtla/osnoise: Record IPI count in osnoise top
  rtla/osnoise: Leverage IPI event filters when tracing a subset of CPUs
  rtla/osnoise: Allow IPI filters to gracefully fail
  rtla: Unconditionally clean any pre-existing filters for user-provided
    events
  rtla/osnoise: Trace IPI events when recording a trace file

 Documentation/tools/rtla/rtla-osnoise-top.rst |   4 +
 tools/tracing/rtla/src/cli.c                  |   1 +
 tools/tracing/rtla/src/cli_p.h                |   3 +
 tools/tracing/rtla/src/common.c               |   2 +-
 tools/tracing/rtla/src/common.h               |   3 +-
 tools/tracing/rtla/src/osnoise.c              |  72 +++++++-
 tools/tracing/rtla/src/osnoise.h              |   4 +
 tools/tracing/rtla/src/osnoise_top.c          | 155 +++++++++++++++++-
 tools/tracing/rtla/src/trace.c                |   4 +
 9 files changed, 244 insertions(+), 4 deletions(-)

--
2.55.0