Re: [PATCH v6 0/9] perf c2c: add a function view

[Namhyung Kim <namhyung@kernel.org>]

Hello,

On Mon, Aug 03, 2026 at 11:52:11AM +0800, Jiebin Sun wrote:
> 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@intel.com/
> v2: https://lore.kernel.org/linux-perf-users/20260710084247.3576706-1-jiebin.sun@intel.com/
> v3: https://lore.kernel.org/linux-perf-users/20260717020530.1645123-1-jiebin.sun@intel.com/
> v4: https://lore.kernel.org/linux-perf-users/20260724095842.995920-1-jiebin.sun@intel.com/
> v5: https://lore.kernel.org/linux-perf-users/20260730090521.2206375-1-jiebin.sun@intel.com/
> 
> 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.

I'm about to merge the series.  But please consider a follow-up work to
add support for --stdio and add a test case.

Thanks,
Namhyung


> 
> 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 helpers 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: each commit builds individually; the full series builds with and
> without SLANG support; perf test c2c passes (one permission-related skip);
> cacheline --stdio output is byte-identical to the base commit; and the
> perf-c2c man page builds.
> 
> 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/Documentation/perf-c2c.txt |   71 +
>  tools/perf/builtin-c2c.c              |  130 +-
>  tools/perf/c2c.h                      |  155 +++
>  tools/perf/ui/browsers/Build          |    1 +
>  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: d04ef71492fad7230d474efe33d05f4c0563d409
> -- 
> 2.52.0
>