[PATCH v2 00/14] perf c2c: add a function view

[Jiebin Sun <jiebin.sun@intel.com>]

This series adds a new "function view" to perf c2c report, on top of the
existing cacheline view. It does not change the cacheline view; it adds a
second, complementary way to look at the same cache-to-cache (C2C) data.

v1: https://lore.kernel.org/linux-perf-users/20260626070355.1556721-1-jiebin.sun@intel.com/

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

  - Add the worked example (the cpupri_set/pull_rt_task walk-through) to
    the perf-c2c man page, as suggested by Namhyung.

  - Rebased onto the latest perf-tools-next.

  - perf c2c: cache the level-1 total-stores sum (new child_stores field)
    instead of walking the children on every comparison. total_stores_cmp()
    is called during collapse/sort, so the previous O(children) walk was an
    O(N*M log N) bottleneck on large profiles.

  - perf c2c: free the function-view sub-hists with
    hists__delete_all_entries() instead of hists__delete_entries(), so
    entries still in the input/collapsed trees are not leaked, matching the
    cleanup in builtin-c2c.c.

  - perf c2c: distinguish -ENOMEM from "unknown dimension" in
    get_function_format(), so an allocation failure is no longer
    misreported as an "Invalid c2c function-view field".

  - perf c2c: reword the iaddr_symbol_cmp() sort-order comment to drop the
    ambiguous ascending/descending wording.

What it does
============

In the perf c2c TUI, press TAB in the cacheline view to switch to the
function view. It presents a 3-level hierarchy:

  Level 1: primary functions, sorted by Cycles % (estimated load cycles:
           HITM, peer-snoop and other-load cycles -- on systems whose
           default display mode is peer, such as Arm64, the peer-snoop
           component dominates)
  Level 2: other functions that share cachelines with the level-1 function
  Level 3: the specific shared cachelines for each function pair

Keys in the function view:
  TAB/ESC/q   return to the cacheline view
  d           show cacheline details for the selected entry
  e / +       expand / collapse the selected entry
  ?           help

The cacheline view and the --stdio output are unchanged.

Example
=======

A level-1 function is expanded (press 'e') to reveal the functions it
shares cachelines with, and one of those is expanded again to reveal the
specific shared cachelines:

  Shared Data Functions Table   (27 entries, sorted on Cycles %)
   Cycles  Store
        %  count  Code address        Symbol           Cacheline
  ----------------------------------------------------------------------
  - 39.03%   541  - 0xffffffffa2fc5b08  - [k] cpupri_set
             450  - 0xffffffffa2fa28a5  - [k] pull_rt_task
             450                                      0xff2d0082809da080

Reading the three levels:

  - Level 1: cpupri_set is the top contended function, accounting for
    39.03% of the estimated load cycles. The table is sorted by this
    Cycles % column.
  - Level 2: expanding cpupri_set (press 'e') lists the functions it
    shares cachelines with, sorted by store count. Here pull_rt_task is
    the contending function, with 450 stores into the shared data.
  - Level 3: expanding pull_rt_task lists the specific cachelines the two
    functions contend over -- in this case the single cacheline at
    0xff2d0082809da080.

The view reads top-down as "cpupri_set is hottest; it shares data with
pull_rt_task; the contention is on cacheline ...da080" -- the false-
sharing chain that the cacheline view otherwise makes you reconstruct by
hand.

Implementation
==============

The function view is built as a separate hist_browser in
tools/perf/ui/browsers/c2c-function.c. Shared types and helpers used by
both views are factored out of builtin-c2c.c into a new c2c.h. The
hierarchy is constructed from the existing cacheline histograms into a
dedicated set of hists, keyed by (symbol, instruction address), and
rendered with custom column formatters.

The series is split into 14 small, self-contained patches so each step
can be reviewed and builds on its own.

Testing
=======

  - Each of the 14 commits builds individually and as a full series.
  - perf c2c report --stdio (cacheline view) output is unchanged versus
    the baseline: identical trace-event totals, shared-cacheline counts,
    and HITM tallies.
  - The function view was exercised on c2c recordings; the level-1
    ordering and the level-2/3 sharing breakdown match the underlying
    cacheline data.

Jiebin Sun (14):
  perf c2c: extract shared data structures into c2c.h
  perf c2c: add function view browser skeleton
  perf c2c: add function view type definitions and helpers
  perf c2c: add column format infrastructure for function view
  perf c2c: add column entry functions for function view
  perf c2c: add comparison functions for function view sorting
  perf c2c: add dimension definitions and format creation
  perf c2c: add HPP list parsing for function view histograms
  perf c2c: add stats merging and memory management helpers
  perf c2c: add hierarchy entry creation and lookup functions
  perf c2c: add function view hierarchy builder
  perf c2c: add function view browser UI
  perf c2c: add TAB key to switch to function view
  perf c2c: document function view in perf-c2c man page

 tools/perf/Documentation/perf-c2c.txt |   33 +
 tools/perf/builtin-c2c.c              |  128 +-
 tools/perf/c2c.h                      |  148 +++
 tools/perf/ui/browsers/Build          |    1 +
 tools/perf/ui/browsers/c2c-function.c | 1563 +++++++++++++++++++++++++
 5 files changed, 1755 insertions(+), 118 deletions(-)
 create mode 100644 tools/perf/c2c.h
 create mode 100644 tools/perf/ui/browsers/c2c-function.c

base-commit: 8c5f60344b07f839267c0c835962e2206143be85
--
2.52.0