Re: [PATCH v3 00/14] perf c2c: add a function view

[Namhyung Kim]

Hello,

On Mon, Jul 20, 2026 at 04:39:24PM +0800, Jiebin Sun wrote:
> Hi Namhyung,
> 
> Thanks a lot for the detailed suggestions -- agreed on both points, and I
> wanted to get your thoughts on the reworked layout before sending the next
> version.
> 
> > I think it's more like "code-address" view rather than "function" view.
> > How about organizing the output something like below?
> >
> >   L1:  function
> >   L2:  cache line
> >   L3:  shared functions
> 
> You're right that keying level 1 on the code address made it read like a
> "code-address view". I plan to rework it so every level that names a
> function aggregates all of that function's code addresses into a single
> entry, together with the per-level indentation you described.
> 
> For the lower levels I first tried the cacheline-then-functions layout you
> suggested:
> 
>   L1: function
>   L2: cache line
>   L3: sharing functions
> 
> but on real data we hit one problem: when the level-1 function touches many
> cache lines, the same contending function shows up under many of those
> level-2 cache lines. To find out which function modifies the line the most
> -- the one most worth fixing -- we then have to aggregate that function's
> writes across all those cache lines ourselves, which is the same manual
> work the cache line view already leaves to us.
> 
> So I am considering putting the contending function at level 2 and the
> cache line at level 3 instead:
> 
>   L1: function            (reads the line and pays the HITM penalty)
>   L2: contending function (writes/modifies the line, causing the HITM)
>   L3: the shared cache lines
> 
> For example, expanding dequeue_pushable_task and its writers:
> 
>   Cycles  Store
>        %  count  Function / Contending function / Cache line
>   ------------------------------------------------------------
>   - 16.54%   419  - [k] dequeue_pushable_task
>              145      - [k] pull_rt_task
>              145            0xff2d0082809da080
>              139      - [k] enqueue_pushable_task
>               70            0xff2d00a2071f9640
>               69            0xff2d0082809da000
>              133      - [k] cpupri_set
>              133            0xff2d0082809da080
> 
> Here enqueue_pushable_task contends over two cache lines, but it stays a
> single level-2 row with its total (139) shown, and the individual cache
> lines are underneath -- so the top writers are ranked directly, with no
> manual summing.
> 
> The key difference from the earlier version is that the code addresses and
> function offsets are no longer shown at level 1 and level 2. Those made the
> view read like a code-address view; instead the main view keeps only the
> concise, at-a-glance information (which function pays, which function it
> contends with, and the cache lines involved), and the detailed code
> addresses / offsets stay in the per-cacheline detail view ('d').
> 
> Once we settle on the layout, I'll send the updated version for review.

Thanks for the explanation and it looks good!

Maybe you can add a shortcut to the cacheline view on the given item in
a follow up work.

Thanks,
Namhyung