[PATCH v7 0/9] perf c2c: add a function view

[Jiebin Sun]

This series adds a new "function view" to perf c2c report, on top of the
existing cacheline view. Existing cacheline-view data and operations remain
unchanged; TAB adds access to a complementary way to inspect the same
cache-to-cache (C2C) data.

v1: https://lore.kernel.org/linux-perf-users/20260626070355.1556721-1-jiebin.sun@xxxxxxxxx/
v2: https://lore.kernel.org/linux-perf-users/20260710084247.3576706-1-jiebin.sun@xxxxxxxxx/
v3: https://lore.kernel.org/linux-perf-users/20260717020530.1645123-1-jiebin.sun@xxxxxxxxx/
v4: https://lore.kernel.org/linux-perf-users/20260724095842.995920-1-jiebin.sun@xxxxxxxxx/
v5: https://lore.kernel.org/linux-perf-users/20260730090521.2206375-1-jiebin.sun@xxxxxxxxx/
v6: https://lore.kernel.org/linux-perf-users/20260803035220.172022-1-jiebin.sun@xxxxxxxxx/

Changes since v6
================

  - Link c2c-function.o directly into perf under CONFIG_SLANG instead of
    including it in libperf-ui.a. The browser depends on state and callbacks
    provided by builtin-c2c.o, which is not linked into python/perf.so,
    while libperf-ui.a is linked under --whole-archive. This fixes the
    unresolved symbols seen when importing the Python module and keeps the
    TUI-only object out of NO_SLANG builds.

  - Rebase onto perf-tools-next at d74fb8c4c87f.

Changes since v5
================

  - Give the function-view children their own references instead of
    borrowing them, as suggested by Namhyung. They set ops and take refs
    via map_symbol__copy() and thread__get(), so hist_entry__delete()
    frees them; the custom child destructor and the
    WARN_ON_ONCE(report_hierarchy) guard are gone.

  - Add NO_SLANG stubs for the two TUI entry points declared in c2c.h,
    matching how util/hist.h declares its own.

  - Spell out in the symbol renderer why the length returned by
    se_snprintf() cannot exceed the cell.

  - Rebase onto perf-tools-next at d04ef71492fa.

No intended change to the rendered output, cacheline-view data, existing
cacheline operations, or --stdio output.

Changes since v4
================

  - Rebase onto perf-tools-next at 0d40fedcd1b9.

  - Require `iaddr` in --coalesce before entering the function view;
    without it, coalesced samples cannot be reliably attributed.

  - Reuse each source cacheline's existing index as the level-3 identity,
    so same-address sources no longer merge and 'd' finds the original
    entry, without adding fields to the shared C2C structures.

  - Keep same-function reader/writer pairs, which the coalesced view cannot
    reliably tell apart from cross-thread contention.

  - Robustness and cleanup: build the hierarchy only from filtered
    cachelines with a lightweight entry allocator; explicit
    mem_info__new() handling; a local bound in the symbol renderer; a
    NULL-map guard; deterministic tie-breaks; function-view-local row
    recounting; Ctrl-C as an exit key; and expanded man-page docs.

Changes since v3
================

Reworked the function view into a true function-centric hierarchy, as
discussed with Namhyung:

  - Level 1 is the read-side function itself, aggregating all of its code
    addresses into one entry and sorting by Cycles %.

  - Level 2 is the contending function that writes the shared lines,
    aggregated across cachelines and sorted by store count. Level 3 is the
    specific cachelines.

  - Dedicated code-address and offset columns were removed from the main
    view. Verbose function formatting can still include a representative
    code address, and full code-address information remains available in
    the per-cacheline detail view ('d').

  - Lower-level entries are indented like the normal perf report hierarchy
    view, and entries with no contending writer are pruned.

  - Reorganized the series from 14 mechanical patches into 9 logically
    self-contained patches.

Changes since v2
================

  - Prefix helpers exported from builtin-c2c.c with c2c_, as suggested by
    Namhyung.

Changes since v1
================

  - Add a worked man-page example, as suggested by Namhyung.

In the perf c2c TUI, press TAB in the cacheline view to switch to the
function view. It presents a three-level hierarchy:

  Level 1: read-side function, sorted by Cycles %
  Level 2: functions writing the shared lines, sorted by store count
  Level 3: cachelines where the two functions contend

For example, with dequeue_pushable_task expanded to its level-2 writers and
two of those writers expanded to their level-3 cachelines:

  Shared Data Functions Table     (19 entries, sorted on Cycles %)
     Cycles    Store
          %    count  Function / Contending function / Cacheline
  ----------------------------------------------------------------------
  +  35.67%      876  + [k] cpupri_set
  +  24.31%      424  + [k] pull_rt_task
  -  16.53%      555  - [k] dequeue_pushable_task
                 145    - [k] pull_rt_task
                 145        0xff2d0082809da080
                 139    - [k] enqueue_pushable_task
                  70        0xff2d00a2071f9640
                  69        0xff2d0082809da000

A level-1 store count decomposes into its level-2 writers, and each writer's
count decomposes into its level-3 cachelines (here 145 = 145, 139 = 70 + 69).

Keys in the function view:

  TAB/ESC/q/Ctrl-C   return to the cacheline view
  d                  show details for the selected level-3 cacheline
  e / +              expand / collapse the selected entry
  ?                  help

The function view is a separate hist_browser in
tools/perf/ui/browsers/c2c-function.c. Shared types and declarations used
by both views are factored out of builtin-c2c.c into c2c.h. The hierarchy
is constructed from the existing cacheline histograms into dedicated hists
and rendered with custom column formatters.

Testing: every commit was clean-built and passed `perf test -v 'import
perf'`. The full series builds with and without SLANG support; the existing
stdio-only `perf test c2c` and the Python import test pass in both
configurations; `ldd -r` reports no unresolved symbols in the Python
extension from either build; and c2c-function.o is no longer included in
libperf-ui.a. Stdio support and automated function-view coverage remain a
separate follow-up.

Jiebin Sun (9):
  perf c2c: extract shared data structures into c2c.h
  perf c2c: add function view browser skeleton
  perf c2c: add column rendering for function view
  perf c2c: add HPP list parsing for function view columns
  perf c2c: add function view stats merge and memory management
  perf c2c: add function view hierarchy entry creation
  perf c2c: build and finalize the function view hierarchy
  perf c2c: add function view browser UI and cacheline detail
  perf c2c: document function view in perf-c2c man page

 tools/perf/Build                      |    1 +
 tools/perf/Documentation/perf-c2c.txt |   71 +
 tools/perf/builtin-c2c.c              |  130 +-
 tools/perf/c2c.h                      |  155 +++
 tools/perf/ui/browsers/c2c-function.c | 1783 +++++++++++++++++++++++++
 5 files changed, 2021 insertions(+), 119 deletions(-)
 create mode 100644 tools/perf/c2c.h
 create mode 100644 tools/perf/ui/browsers/c2c-function.c


base-commit: d74fb8c4c87f10fd147114133f786a10f7e58d8a
-- 
2.52.0