linux-kernel - [PATCH v14 00/11] perf: Support the deferred unwinding infrastructure

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Message-ID: <20250718164119.089692174@kernel.org>
Date: Fri, 18 Jul 2025 12:41:19 -0400
From: Steven Rostedt <rostedt@...nel.org>
To: linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org,
 bpf@...r.kernel.org,
 x86@...nel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Josh Poimboeuf <jpoimboe@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...nel.org>,
 Jiri Olsa <jolsa@...nel.org>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>,
 Andrii Nakryiko <andrii@...nel.org>,
 Indu Bhagat <indu.bhagat@...cle.com>,
 "Jose E. Marchesi" <jemarch@....org>,
 Beau Belgrave <beaub@...ux.microsoft.com>,
 Jens Remus <jremus@...ux.ibm.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Jens Axboe <axboe@...nel.dk>,
 Florian Weimer <fweimer@...hat.com>,
 Sam James <sam@...too.org>
Subject: [PATCH v14 00/11] perf: Support the deferred unwinding infrastructure

This is based on top of the deferred unwind core patch series:

 https://lore.kernel.org/linux-trace-kernel/20250717004910.297898999@kernel.org/
   git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
     unwind/core

This series implements the perf interface to use deferred user space stack
tracing.

The first 5 patches are clean ups and simplifications. There's a standalone
series with these patches here:

  https://lore.kernel.org/linux-trace-kernel/20250717173125.434618999@kernel.org/


Patch 6 implements a task deferred tracing that works with events following
a specific task (per thread).

Patch 7 implements a per CPU deferred tracing that requires the application
(perf user space) to have a per CPU event buffer for every CPU where a task
may migrate to from the time a deferred request is made to when the stack
trace occurs, as a task may migrate to a different CPU after the request and
before it goes back to user space.

The rest of the patches implement the tool side of perf.

KNOWN ISSUES:

- The marker that adds the USER_DEFERRED when the request was made, should
  also add the cookie. As the cookie can be used to figure out if dropped
  events missed a stack trace and not to attach a stack trace to the wrong
  events.

- The writing of the stack trace should probably be changed to act more like
  get_perf_callchain() where it does fixups to uprobes.

The code for this series is located here:

  git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
unwind/perf

Head SHA1: 5753b61c16f61e50f35bf0f3dfbf8a00b8de2d51

Changes since v13: https://lore.kernel.org/linux-trace-kernel/20250708020003.565862284@kernel.org/

- Missed one location to replace the current->mm == NULL check that still
  only checked PF_KTHREAD. It must also check PF_USER_WORKER.

- Need to copy the trace.entries[] one a at a time as the perf entry in
  the ring buffer has 64 bit entries, but trace.entries[] are size long.
 
- Added back the cookie field in perf_callchain_deferred_event structure
  (Note, it was a timestamp before) (Namhyung Kim)
 
- Add the cookie to the comment explaining perf_callchain_deferred_event.

- Fixed deferred_unwind_request() to return 1 if the request was already
  queued or was already executed to not incorrectly increment
  nr_no_switch_fast.

- Display the cookie in the -D output


Josh Poimboeuf (5):
      perf: Remove get_perf_callchain() init_nr argument
      perf: Have get_perf_callchain() return NULL if crosstask and user are set
      perf: Simplify get_perf_callchain() user logic
      perf: Skip user unwind if the task is a kernel thread
      perf: Support deferred user callchains

Namhyung Kim (4):
      perf tools: Minimal CALLCHAIN_DEFERRED support
      perf record: Enable defer_callchain for user callchains
      perf script: Display PERF_RECORD_CALLCHAIN_DEFERRED
      perf tools: Merge deferred user callchains

Steven Rostedt (2):
      perf: Use current->flags & PF_KTHREAD|PF_USER_WORKER instead of current->mm == NULL
      perf: Support deferred user callchains for per CPU events

----
 include/linux/perf_event.h                |  13 +-
 include/uapi/linux/perf_event.h           |  20 +-
 kernel/bpf/stackmap.c                     |   8 +-
 kernel/events/callchain.c                 |  49 ++--
 kernel/events/core.c                      | 424 +++++++++++++++++++++++++++++-
 tools/include/uapi/linux/perf_event.h     |  19 +-
 tools/lib/perf/include/perf/event.h       |   8 +
 tools/perf/Documentation/perf-script.txt  |   5 +
 tools/perf/builtin-script.c               |  92 +++++++
 tools/perf/util/callchain.c               |  24 ++
 tools/perf/util/callchain.h               |   3 +
 tools/perf/util/event.c                   |   1 +
 tools/perf/util/evlist.c                  |   1 +
 tools/perf/util/evlist.h                  |   1 +
 tools/perf/util/evsel.c                   |  39 +++
 tools/perf/util/evsel.h                   |   1 +
 tools/perf/util/machine.c                 |   1 +
 tools/perf/util/perf_event_attr_fprintf.c |   1 +
 tools/perf/util/sample.h                  |   3 +-
 tools/perf/util/session.c                 |  79 ++++++
 tools/perf/util/tool.c                    |   2 +
 tools/perf/util/tool.h                    |   4 +-
 22 files changed, 762 insertions(+), 36 deletions(-)