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    Subject[PATCH 63/69] libperf: Centralize map refcnt setting
    Date
    From: Jiri Olsa <jolsa@kernel.org>

    Currently when a new map is mmapped we set its refcnt to 2 in the
    perf_evlist_mmap_ops::mmap callback.

    Every mmap gets its refcnt set to 2 when it's first mmaped:

    - 1 for the current user, which will be taken out by a call to
    perf_evlist__munmap_filtered(), where we find out there's
    no more data comming from kernel to this mmap.

    - 1 for the drain code where in perf_mmap__consume() the mmap
    is released if it is empty.

    Move this common setup into libperf's generic code before the mmap
    callback is called.

    Signed-off-by: Jiri Olsa <jolsa@kernel.org>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Michael Petlan <mpetlan@redhat.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Link: http://lore.kernel.org/lkml/20191007125344.14268-23-jolsa@kernel.org
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    ---
    tools/perf/lib/evlist.c | 30 +++++++++++++++---------------
    tools/perf/util/mmap.c | 15 ---------------
    2 files changed, 15 insertions(+), 30 deletions(-)

    diff --git a/tools/perf/lib/evlist.c b/tools/perf/lib/evlist.c
    index b69722627779..f9a802d2ceb5 100644
    --- a/tools/perf/lib/evlist.c
    +++ b/tools/perf/lib/evlist.c
    @@ -362,21 +362,6 @@ static int
    perf_evlist__mmap_cb_mmap(struct perf_mmap *map, struct perf_mmap_param *mp,
    int output, int cpu)
    {
    - /*
    - * The last one will be done at perf_mmap__consume(), so that we
    - * make sure we don't prevent tools from consuming every last event in
    - * the ring buffer.
    - *
    - * I.e. we can get the POLLHUP meaning that the fd doesn't exist
    - * anymore, but the last events for it are still in the ring buffer,
    - * waiting to be consumed.
    - *
    - * Tools can chose to ignore this at their own discretion, but the
    - * evlist layer can't just drop it when filtering events in
    - * perf_evlist__filter_pollfd().
    - */
    - refcount_set(&map->refcnt, 2);
    -
    return perf_mmap__mmap(map, mp, output, cpu);
    }

    @@ -418,6 +403,21 @@ mmap_per_evsel(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
    if (*output == -1) {
    *output = fd;

    + /*
    + * The last one will be done at perf_mmap__consume(), so that we
    + * make sure we don't prevent tools from consuming every last event in
    + * the ring buffer.
    + *
    + * I.e. we can get the POLLHUP meaning that the fd doesn't exist
    + * anymore, but the last events for it are still in the ring buffer,
    + * waiting to be consumed.
    + *
    + * Tools can chose to ignore this at their own discretion, but the
    + * evlist layer can't just drop it when filtering events in
    + * perf_evlist__filter_pollfd().
    + */
    + refcount_set(&map->refcnt, 2);
    +
    if (ops->mmap(map, mp, *output, evlist_cpu) < 0)
    return -1;
    } else {
    diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
    index 2a8bf0ab861c..063d1b93c53d 100644
    --- a/tools/perf/util/mmap.c
    +++ b/tools/perf/util/mmap.c
    @@ -243,21 +243,6 @@ static void perf_mmap__setup_affinity_mask(struct mmap *map, struct mmap_params

    int mmap__mmap(struct mmap *map, struct mmap_params *mp, int fd, int cpu)
    {
    - /*
    - * The last one will be done at perf_mmap__consume(), so that we
    - * make sure we don't prevent tools from consuming every last event in
    - * the ring buffer.
    - *
    - * I.e. we can get the POLLHUP meaning that the fd doesn't exist
    - * anymore, but the last events for it are still in the ring buffer,
    - * waiting to be consumed.
    - *
    - * Tools can chose to ignore this at their own discretion, but the
    - * evlist layer can't just drop it when filtering events in
    - * perf_evlist__filter_pollfd().
    - */
    - refcount_set(&map->core.refcnt, 2);
    -
    if (perf_mmap__mmap(&map->core, &mp->core, fd, cpu)) {
    pr_debug2("failed to mmap perf event ring buffer, error %d\n",
    errno);
    --
    2.21.0
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