From: Tom Zanussi 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. Link: http://lkml.kernel.org/r/427bed1389c5d22aa40c3e0683e30cc3d151e260.1516069914.git.tom.zanussi@linux.intel.com Signed-off-by: Tom Zanussi Signed-off-by: Rajvi Jingar Signed-off-by: Steven Rostedt (VMware) --- Documentation/trace/histogram.txt | 11 +++++++++- kernel/trace/trace_events_hist.c | 42 ++++++++++++++++++++++++++++++++++++--- 2 files changed, 49 insertions(+), 4 deletions(-) diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt index df08882d091c..6e05510afc28 100644 --- a/Documentation/trace/histogram.txt +++ b/Documentation/trace/histogram.txt @@ -1671,7 +1671,16 @@ features have been added to the hist trigger support: 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 8719b0ea672f..f7d0da20c5c8 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; @@ -1776,6 +1777,7 @@ 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); } @@ -1831,6 +1833,19 @@ 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); @@ -1895,6 +1910,14 @@ 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); @@ -4934,6 +4957,8 @@ 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); @@ -5201,7 +5226,6 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops, data->paused = true; if (named_data) { - destroy_hist_data(data->private_data); data->private_data = named_data->private_data; set_named_trigger_data(data, named_data); data->ops = &event_hist_trigger_named_ops; @@ -5213,10 +5237,22 @@ 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); + } + + if (named_data) + destroy_hist_data(hist_data); + + ret++; out: return ret; } -- 2.15.1