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    Subject[PATCH 39/48] perf tools: Detect avalibility of write_backward
    Date
    Detect avalibility of write_backward and save the result into
    record_opts. With write_backward the start pointer of a ring
    buffer mapped read only can be found reliably.

    Signed-off-by: Wang Nan <wangnan0@huawei.com>
    Signed-off-by: He Kuang <hekuang@huawei.com>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Jiri Olsa <jolsa@kernel.org>
    Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Zefan Li <lizefan@huawei.com>
    Cc: pi3orama@163.com
    ---
    tools/perf/perf.h | 1 +
    tools/perf/util/record.c | 11 +++++++++++
    2 files changed, 12 insertions(+)

    diff --git a/tools/perf/perf.h b/tools/perf/perf.h
    index 5381a01..198345e 100644
    --- a/tools/perf/perf.h
    +++ b/tools/perf/perf.h
    @@ -73,6 +73,7 @@ struct record_opts {
    bool sample_transaction;
    unsigned initial_delay;
    bool use_clockid;
    + bool has_write_backward;
    clockid_t clockid;
    unsigned int proc_map_timeout;
    };
    diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
    index 0467367..d01f155 100644
    --- a/tools/perf/util/record.c
    +++ b/tools/perf/util/record.c
    @@ -85,6 +85,11 @@ static void perf_probe_comm_exec(struct perf_evsel *evsel)
    evsel->attr.comm_exec = 1;
    }

    +static void perf_probe_write_backward(struct perf_evsel *evsel)
    +{
    + evsel->attr.write_backward = 1;
    +}
    +
    static void perf_probe_context_switch(struct perf_evsel *evsel)
    {
    evsel->attr.context_switch = 1;
    @@ -105,6 +110,11 @@ bool perf_can_record_switch_events(void)
    return perf_probe_api(perf_probe_context_switch);
    }

    +static bool perf_can_write_backward(void)
    +{
    + return perf_probe_api(perf_probe_write_backward);
    +}
    +
    bool perf_can_record_cpu_wide(void)
    {
    struct perf_event_attr attr = {
    @@ -235,6 +245,7 @@ static int record_opts__config_freq(struct record_opts *opts)

    int record_opts__config(struct record_opts *opts)
    {
    + opts->has_write_backward = perf_can_write_backward();
    return record_opts__config_freq(opts);
    }

    --
    1.8.3.4
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