linux-kernel - Re: [PATCH 00/22] Refactor perf cpumap

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Message-ID: <CAP-5=fWkJdW3Jr1NX115=nWdGhUvPMbMzi5fZZ0-REUSq-bkig@mail.gmail.com>
Date:   Mon, 13 Dec 2021 14:06:43 -0800
From:   Ian Rogers <irogers@...gle.com>
To:     James Clark <james.clark@....com>
Cc:     eranian@...gle.com, Andi Kleen <ak@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        "Paul A . Clarke" <pc@...ibm.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Riccardo Mancini <rickyman7@...il.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vineet Singh <vineet.singh@...el.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 00/22] Refactor perf cpumap

On Mon, Dec 13, 2021 at 8:10 AM Ian Rogers <irogers@...gle.com> wrote:
>
> On Mon, Dec 13, 2021 at 3:39 AM James Clark <james.clark@....com> wrote:
> >
> >
> >
> > On 08/12/2021 02:45, Ian Rogers wrote:
> > > Perf cpu map has various functions where a cpumap and index are passed
> > > in order to load the cpu. A problem with this is that the wrong index
> > > may be passed for the cpumap, causing problems like aggregation on the
> > > wrong CPU:
> > > https://lore.kernel.org/lkml/20211204023409.969668-1-irogers@google.com/
> > >
> > > This patch set refactors the cpu map API, greatly reducing it and
> > > explicitly passing the cpu (rather than the pair) to functions that
> > > need it. Comments are added at the same time.
> > >
> > > Ian Rogers (22):
> > >   libperf: Add comments to perf_cpu_map.
> > >   perf stat: Add aggr creators that are passed a cpu.
> > >   perf stat: Switch aggregation to use for_each loop
> > >   perf stat: Switch to cpu version of cpu_map__get
> > >   perf cpumap: Switch cpu_map__build_map to cpu function
> > >   perf cpumap: Remove map+index get_socket
> > >   perf cpumap: Remove map+index get_die
> > >   perf cpumap: Remove map+index get_core
> > >   perf cpumap: Remove map+index get_node
> > >   perf cpumap: Add comments to aggr_cpu_id
> > >   perf cpumap: Remove unused cpu_map__socket
> > >   perf cpumap: Simplify equal function name.
> > >   perf cpumap: Rename empty functions.
> > >   perf cpumap: Document cpu__get_node and remove redundant function
> > >   perf cpumap: Remove map from function names that don't use a map.
> > >   perf cpumap: Remove cpu_map__cpu, use libperf function.
> > >   perf cpumap: Refactor cpu_map__build_map
> > >   perf cpumap: Rename cpu_map__get_X_aggr_by_cpu functions
> > >   perf cpumap: Move 'has' function to libperf
> > >   perf cpumap: Add some comments to cpu_aggr_map
> > >   perf cpumap: Trim the cpu_aggr_map
> > >   perf stat: Fix memory leak in check_per_pkg
> > >
> > >  tools/lib/perf/cpumap.c                  |   7 +-
> > >  tools/lib/perf/include/internal/cpumap.h |   9 +-
> > >  tools/lib/perf/include/perf/cpumap.h     |   1 +
> > >  tools/perf/arch/arm/util/cs-etm.c        |  16 +-
> > >  tools/perf/builtin-ftrace.c              |   2 +-
> > >  tools/perf/builtin-sched.c               |   6 +-
> > >  tools/perf/builtin-stat.c                | 273 ++++++++++++-----------
> > >  tools/perf/tests/topology.c              |  10 +-
> > >  tools/perf/util/cpumap.c                 | 182 ++++++---------
> > >  tools/perf/util/cpumap.h                 | 102 ++++++---
> > >  tools/perf/util/cputopo.c                |   2 +-
> > >  tools/perf/util/env.c                    |   6 +-
> > >  tools/perf/util/stat-display.c           |  69 +++---
> > >  tools/perf/util/stat.c                   |   9 +-
> > >  tools/perf/util/stat.h                   |   3 +-
> > >  15 files changed, 361 insertions(+), 336 deletions(-)
> > >
> >
> > For the whole set:
> >
> > Reviewed-by: James Clark <james.clark@....com>
> >
> > I didn't see any obvious issues with mixing up aggregation modes or CPU/idx types. Also
> > gave perf stat a test in the different modes and didn't see an issue.
> >
> > But I'm wondering if it's possible to go further and add a struct around the CPU int so that the
> > compiler checks for correctness instead. It still seems quite easy to mix up index and
> > CPU, for example these functions are subtly different, but both use int:
> >
> >   LIBPERF_API int perf_cpu_map__cpu(const struct perf_cpu_map *cpus, int idx);
> >   LIBPERF_API bool perf_cpu_map__has(const struct perf_cpu_map *map, int cpu);
> >
> > Something like this would make it impossible to make a mistake:
> >
> >   struct cpu { int cpu };
> >
> > I mean it's more of a coincidence that CPUs can be identified by an integer, but they are more
> > of an object than an integer, so it could make sense to wrap it. But maybe it could be quite
> > cumbersome to use and be overkill.
>
> Thanks James! I am working on a v2 patch set and will have a go at
> adding this to the end.
>
> Ian

I was checking on the style issues around wrapping an int with a
struct, and it is preferred style to enforce strict type checking (by
way of an old post):
https://lore.kernel.org/all/ancug3$iq1$1@penguin.transmeta.com/

Thanks,
Ian