linux-kernel - [RFC PATCH 0/5] tracing/filters: filtering event fields with a cpumask

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Date:   Fri,  9 Jun 2023 16:03:19 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Juri Lelli <juri.lelli@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Leonardo Bras <leobras@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: [RFC PATCH 0/5] tracing/filters: filtering event fields with a cpumask

Hi folks,

In the context of CPU isolation / NOHZ_FULL interference investigation, we now
have the ipi_send_cpu and ipi_send_cpumask events. However, enabling these
events without any filtering can yield pretty massive traces with a lot of
uninteresting or irrelevant data (e.g. everything targeting housekeeping CPUs).

This series is about adding event filtering via a user-provided cpumask. This
enables filtering using cpumask fields (e.g. ipi_send_cpumask) and extends this
to scalar and the local CPU common fields.

With this, it becomes fairly easy to trace events both happening on and
targeting CPUs of interest, e.g.:

  trace-cmd record -e 'sched_switch' -f "CPU & MASK{$ISOLATED_CPUS}"         \
		   -e 'sched_wakeup' -f "target_cpu & MASK{$ISOLATED_CPUS}"  \
		   -e 'ipi_send_cpu' -f "cpu & MASK{$ISOLATED_CPUS}"         \
		   -e 'ipi_send_cpumask' -f "cpumask & MASK{$ISOLATED_CPUS}" \
		   hackbench

The MASK{} thing is a bit crude but seems to work well enough without break^C
overhauling the predicate parsing logic.

Cheers,
Valentin

Valentin Schneider (5):
  tracing/filters: Dynamically allocate filter_pred.regex
  tracing/filters: Enable filtering a cpumask field by another cpumask
  tracing/filters: Enable filtering a scalar field by a cpumask
  tracing/filters: Enable filtering the CPU common field by a cpumask
  tracing/filters: Document cpumask filtering

 Documentation/trace/events.rst     |  14 ++
 include/linux/trace_events.h       |   1 +
 kernel/trace/trace_events_filter.c | 228 +++++++++++++++++++++++++----
 3 files changed, 216 insertions(+), 27 deletions(-)

--
2.31.1