linux-kernel - [PATCH v9 0/4] Some new features for the preempt/irqsoff tracers

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Date:   Tue, 15 Oct 2019 13:19:06 +0200
From:   "Viktor Rosendahl (BMW)" <viktor.rosendahl@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        "Viktor Rosendahl (BMW)" <viktor.rosendahl@...il.com>
Subject: [PATCH v9 0/4] Some new features for the preempt/irqsoff tracers

Hello all,

Changes in v9:

- [PATCH 1/4]:
  * Rebased the patch for v5.4-rc3+
  * Dropped support for the hwlat tracer. It seems to me, both from testing
    and looking at the code, that hwlat doesn't actually update
    /sys/kernel/debug/tracing/tracing_max_latency. I think it would be a bit
    weird to send fsnotify for changes to a file that are not visible to
    userspace. Also, the hwlat use case is not very interesting from
    my perspective because hwlat works in non-overwrite mode by default. For me,
    the effort needed to make it work properly would be more than what it's
    worth.
  * Because of the changes mentioned above, I removed the Reviewed-by tag.

- [PATCH 2/4]:
  * No change.

- [PATCH 3/4]:
  * Removed the mention of hwlat from the commit and help messages.

- [PACTH 4/4]:
  * Changed the trace-option to a kernel parameter. This would hopefully make
    it easier to remove it if it becomes obsolete.

This series is meant to address two issues with the latency tracing.

The first three patches provide a method to trace latencies that always
occurs very close to each other and to differentiate between them, in spite
of the fact that the latency tracers work in overwrite mode.

[PATCH 1/4] This implement fs notification for tracing_max_latency. It
makes it possible for userspace to detect when a new latency has been
detected.

[PATCH 2/4] This extends the preemptirq_delay_test module so that it can be
used to generate a burst of closely occurring latencies.

[PATCH 3/4] This adds a user space program to the tools directory that
utilizes the fs notification feature and a randomized algorithm to print out
any of the latencies in a burst with approximately equal probability.

The last patch is not directly connected but earlier it didn't apply
cleanly on its own. However, now it does, so in principle it could be
applied separately from the others.

[PATCH 4/4] This adds the option console-latency to the trace options. This
makes it possible to enable tracing of console latencies.

best regards,

Viktor

Viktor Rosendahl (BMW) (4):
  ftrace: Implement fs notification for tracing_max_latency
  preemptirq_delay_test: Add the burst feature and a sysfs trigger
  Add the latency-collector to tools
  ftrace: Add an option for tracing console latencies

 .../admin-guide/kernel-parameters.txt         |    4 +
 include/linux/irqflags.h                      |   22 +
 kernel/printk/printk.c                        |    6 +-
 kernel/trace/Kconfig                          |    6 +-
 kernel/trace/preemptirq_delay_test.c          |  144 +-
 kernel/trace/trace.c                          |   75 +-
 kernel/trace/trace.h                          |   18 +
 kernel/trace/trace_irqsoff.c                  |   32 +
 tools/Makefile                                |   14 +-
 tools/trace/Makefile                          |   20 +
 tools/trace/latency-collector.c               | 1212 +++++++++++++++++
 11 files changed, 1521 insertions(+), 32 deletions(-)
 create mode 100644 tools/trace/Makefile
 create mode 100644 tools/trace/latency-collector.c

-- 
2.17.1