[PATCH v8 0/9] perf c2c: add a function view
From: Jiebin Sun
Date: Mon Aug 10 2026 - 01:20:31 EST
The perf c2c cacheline view identifies hot shared lines, but it can be
difficult to see which functions account for contention across those lines.
This series adds a function-oriented view that groups the existing data as:
read-side function -> contending writer -> shared cacheline
Pressing TAB switches between the cacheline and function views. Existing
cacheline-view data and operations remain unchanged.
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/
v7: https://lore.kernel.org/linux-perf-users/20260806074217.2846596-1-jiebin.sun@xxxxxxxxx/
Changes since v7
================
- Keep c2c-function.o in libperf-ui.a and drop the v7 tools/perf/Build
change, as Namhyung suggested. builtin-c2c.c now passes the cacheline
histograms, coalescing fields, symbol_full flag, and cacheline detail
callback through struct c2c_function_view_args. The browser no longer
references command-private state.
- Move the shared c2c types and the two column-formatting callbacks into
new util/c2c.h and util/c2c.c. Keep struct perf_c2c, the command
instance, and perf_c2c__browse_cacheline() private to builtin-c2c.c.
- Rebase onto perf-tools-next at bf10e6ee2ac3.
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 util/c2c.h. The
hierarchy is constructed from the existing cacheline histograms into
dedicated hists and rendered with custom column formatters.
Testing: every commit builds with and without SLANG support. In both
configurations python/perf.so has no unresolved symbols, the Python module
imports successfully, and the full series passes `perf test c2c` and
`perf test 'import perf'`. The cacheline-view --stdio output is
byte-identical to the base commit. c2c-function.o remains in libperf-ui.a
without references to command-private symbols. Stdio support and automated
function-view coverage remain a separate follow-up.
Jiebin Sun (9):
perf c2c: extract shared data structures into util/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/Documentation/perf-c2c.txt | 71 +
tools/perf/builtin-c2c.c | 115 +-
tools/perf/ui/browsers/Build | 1 +
tools/perf/ui/browsers/c2c-function.c | 1791 +++++++++++++++++++++++++
tools/perf/util/Build | 1 +
tools/perf/util/c2c.c | 21 +
tools/perf/util/c2c.h | 131 ++
7 files changed, 2029 insertions(+), 102 deletions(-)
create mode 100644 tools/perf/ui/browsers/c2c-function.c
create mode 100644 tools/perf/util/c2c.c
create mode 100644 tools/perf/util/c2c.h
base-commit: bf10e6ee2ac3034c9068e03eed418fd16961984e
--
2.52.0