linux-kernel - Re: [PATCHSET 0/9] perf annotate-data: Update data-type profiling quality (v1)

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Message-ID: <ZsOeaPxZu1bAobUs@x1>
Date: Mon, 19 Aug 2024 16:35:04 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Ian Rogers <irogers@...gle.com>, Kan Liang <kan.liang@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org,
	Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
Subject: Re: [PATCHSET 0/9] perf annotate-data: Update data-type profiling
 quality (v1)

On Fri, Aug 16, 2024 at 04:58:30PM -0700, Namhyung Kim wrote:
> Hello,
> 
> I've found a couple of bugs in the DWARF location handling and had
> some updates to improve the quality of the type resolution.
> 
> The current code only checks the first variable it found in the
> closest scope but sometimes it's not good because macro expansions
> like container_of (which is used by many list/rb tree manipulation
> routines) only gives a very limited information (like void *) with
> type cast.  So it needs to lookup other variables in the upper scope.
> See the patch 8 for more details.
> 
> Also sometimes it can have more information for the parent type if the
> pointer is for an embedded type.  For example, a list_head is
> typically a part of bigger struct.  Even if it found a variable for
> the list_head, it'd be nice if it can tell which list it is.
> 
> To compare two type information in general, I've added a heuristic to
> take a pointer to a bigger data type.
> 
> This is an example data, the portion of unknown type went down a bit
> and the atomic_t turned out to be _mapcount in the struct page.
> 
> Before:
>   #
>   # Overhead  Data Type
>   # ........  .........
>   #
>       37.24%  (unknown)
>       14.40%  atomic_t 
>        8.81%  (stack operation)
>        5.54%  struct psi_group_cpu
>        3.40%  struct task_struct
>        2.99%  struct pcpu_hot
>        2.99%  struct cfs_rq
>        2.18%  struct audit_krule
>        1.93%  struct psi_group
>        1.62%  struct sched_entity
> 
> After:
>   #
>   # Overhead  Data Type
>   # ........  .........
>   #
>       36.87%  (unknown)
>       14.40%  struct page
>        8.81%  (stack operation)
>        6.00%  struct psi_group_cpu
>        3.40%  struct task_struct
>        3.36%  struct cfs_rq
>        2.99%  struct pcpu_hot
>        2.18%  struct audit_krule
>        1.93%  struct psi_group
>        1.62%  struct sched_entity
> 
> Also updated the debug message and the statistics to help debugging.
> 
> The code is available at 'perf/data-profile-update-v1' branch in
> git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git
> 

Thanks, applied to perf-tools-next,

- Arnaldo