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    Subject[PATCH v4 34/37] tracing: Add a clock attribute for hist triggers
    Date
    The default clock if timestamps are used in a histogram is "global".
    If timestamps aren't used, the clock is irrelevant.

    Use the "clock=" param only if you want to override the default
    "global" clock for a histogram with timestamps.

    Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
    Signed-off-by: Rajvi Jingar <rajvi.jingar@intel.com>
    ---
    Documentation/trace/histogram.txt | 11 ++++++++++-
    kernel/trace/trace_events_hist.c | 38 ++++++++++++++++++++++++++++++++++++--
    2 files changed, 46 insertions(+), 3 deletions(-)

    diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt
    index 0eea8b9..aa450bb 100644
    --- a/Documentation/trace/histogram.txt
    +++ b/Documentation/trace/histogram.txt
    @@ -1674,7 +1674,16 @@ features have been added to the hist trigger support:
    default it is in units of nanoseconds; appending '.usecs' to a
    common_timestamp field changes the units to microseconds.

    -These features are decribed in more detail in the following sections.
    +A note on inter-event timestamps: If $common_timestamp is used in a
    +histogram, the trace buffer is automatically switched over to using
    +absolute timestamps and the "global" trace clock, in order to avoid
    +bogus timestamp differences with other clocks that aren't coherent
    +across CPUs. This can be overridden by specifying one of the other
    +trace clocks instead, using the "clock=XXX" hist trigger attribute,
    +where XXX is any of the clocks listed in the tracing/trace_clock
    +pseudo-file.
    +
    +These features are described in more detail in the following sections.

    2.2.1 Histogram Variables
    -------------------------
    diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
    index acebaae..686fbca 100644
    --- a/kernel/trace/trace_events_hist.c
    +++ b/kernel/trace/trace_events_hist.c
    @@ -242,6 +242,7 @@ struct hist_trigger_attrs {
    char *vals_str;
    char *sort_key_str;
    char *name;
    + char *clock;
    bool pause;
    bool cont;
    bool clear;
    @@ -1790,6 +1791,7 @@ static void destroy_hist_trigger_attrs(struct hist_trigger_attrs *attrs)
    kfree(attrs->sort_key_str);
    kfree(attrs->keys_str);
    kfree(attrs->vals_str);
    + kfree(attrs->clock);
    kfree(attrs);
    }

    @@ -1845,6 +1847,19 @@ static int parse_assignment(char *str, struct hist_trigger_attrs *attrs)
    ret = -ENOMEM;
    goto out;
    }
    + } else if (strncmp(str, "clock=", strlen("clock=")) == 0) {
    + strsep(&str, "=");
    + if (!str) {
    + ret = -EINVAL;
    + goto out;
    + }
    +
    + str = strstrip(str);
    + attrs->clock = kstrdup(str, GFP_KERNEL);
    + if (!attrs->clock) {
    + ret = -ENOMEM;
    + goto out;
    + }
    } else if (strncmp(str, "size=", strlen("size=")) == 0) {
    int map_bits = parse_map_size(str);

    @@ -1908,6 +1923,14 @@ static struct hist_trigger_attrs *parse_hist_trigger_attrs(char *trigger_str)
    goto free;
    }

    + if (!attrs->clock) {
    + attrs->clock = kstrdup("global", GFP_KERNEL);
    + if (!attrs->clock) {
    + ret = -ENOMEM;
    + goto free;
    + }
    + }
    +
    return attrs;
    free:
    destroy_hist_trigger_attrs(attrs);
    @@ -4917,6 +4940,8 @@ static int event_hist_trigger_print(struct seq_file *m,
    seq_puts(m, ".descending");
    }
    seq_printf(m, ":size=%u", (1 << hist_data->map->map_bits));
    + if (hist_data->enable_timestamps)
    + seq_printf(m, ":clock=%s", hist_data->attrs->clock);

    print_actions_spec(m, hist_data);

    @@ -5179,10 +5204,19 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
    goto out;
    }

    - ret++;
    + if (hist_data->enable_timestamps) {
    + char *clock = hist_data->attrs->clock;
    +
    + ret = tracing_set_clock(file->tr, hist_data->attrs->clock);
    + if (ret) {
    + hist_err("Couldn't set trace_clock: ", clock);
    + goto out;
    + }

    - if (hist_data->enable_timestamps)
    tracing_set_time_stamp_abs(file->tr, true);
    + }
    +
    + ret++;
    out:
    return ret;
    }
    --
    1.9.3
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