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SubjectRe: [PATCH 00/22] Refactor perf cpumap
On Mon, Dec 13, 2021 at 8:10 AM Ian Rogers <irogers@google.com> wrote:
>
> On Mon, Dec 13, 2021 at 3:39 AM James Clark <james.clark@arm.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@arm.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

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