Re: [PATCH v6 29/37] tracing: Add cpu field for hist triggers

Namhyung Kim
2017-11-23T05:26:01Z

On Fri, Nov 17, 2017 at 02:33:08PM -0600, Tom Zanussi wrote:
> A common key to use in a histogram is the cpuid - add a new cpu
> 'synthetic' field for that purpose. This field is named cpu rather
> than $cpu or $common_cpu because 'cpu' already exists as a special
> filter field and it makes more sense to match that rather than add
> another name for the same thing.
>
> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
> ---
> Documentation/trace/histogram.txt | 17 +++++++++++++++++
> kernel/trace/trace_events_hist.c | 28 +++++++++++++++++++++++++++-
> 2 files changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt
> index d1d92ed..cd3ec00 100644
> --- a/Documentation/trace/histogram.txt
> +++ b/Documentation/trace/histogram.txt
> @@ -172,6 +172,23 @@
> The examples below provide a more concrete illustration of the
> concepts and typical usage patterns discussed above.
>
> + 'special' event fields
> + ------------------------
> +
> + There are a number of 'special event fields' available for use as
> + keys or values in a hist trigger. These look like and behave as if
> + they were actual event fields, but aren't really part of the event's
> + field definition or format file. They are however available for any
> + event, and can be used anywhere an actual event field could be.
> + 'Special' field names are always prefixed with a '$' character to
> + indicate that they're not normal fields (with the exception of
> + 'cpu', for compatibility with existing filter usage):

But it also could make a confusion to variables. How about removing
'$' character at all?

> +
> + $common_timestamp u64 - timestamp (from ring buffer) associated
> + with the event, in nanoseconds. May be
> + modified by .usecs to have timestamps
> + interpreted as microseconds.
> + cpu int - the cpu on which the event occurred.
>
> 6.2 'hist' trigger examples
> ---------------------------
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 121f7ef..afbfa9c 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -227,6 +227,7 @@ enum hist_field_flags {
> HIST_FIELD_FL_VAR = 1 << 12,
> HIST_FIELD_FL_EXPR = 1 << 13,
> HIST_FIELD_FL_VAR_REF = 1 << 14,
> + HIST_FIELD_FL_CPU = 1 << 15,
> };
>
> struct var_defs {
> @@ -1177,6 +1178,16 @@ static u64 hist_field_timestamp(struct hist_field *hist_field,
> return ts;
> }
>
> +static u64 hist_field_cpu(struct hist_field *hist_field,
> + struct tracing_map_elt *elt,
> + struct ring_buffer_event *rbe,
> + void *event)
> +{
> + int cpu = smp_processor_id();
> +
> + return cpu;
> +}
> +
> static struct hist_field *
> check_field_for_var_ref(struct hist_field *hist_field,
> struct hist_trigger_data *var_data,
> @@ -1622,6 +1633,8 @@ static const char *hist_field_name(struct hist_field *field,
> field_name = hist_field_name(field->operands[0], ++level);
> else if (field->flags & HIST_FIELD_FL_TIMESTAMP)
> field_name = "$common_timestamp";
> + else if (field->flags & HIST_FIELD_FL_CPU)
> + field_name = "cpu";
> else if (field->flags & HIST_FIELD_FL_EXPR ||
> field->flags & HIST_FIELD_FL_VAR_REF) {
> if (field->system) {
> @@ -2125,6 +2138,15 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
> goto out;
> }
>
> + if (flags & HIST_FIELD_FL_CPU) {
> + hist_field->fn = hist_field_cpu;
> + hist_field->size = sizeof(int);
> + hist_field->type = kstrdup("int", GFP_KERNEL);

Is it unsigned?

Thanks,
Namhyung

> + if (!hist_field->type)
> + goto free;
> + goto out;
> + }
> +
> if (WARN_ON_ONCE(!field))
> goto out;
>
> @@ -2343,7 +2365,9 @@ static struct hist_field *parse_var_ref(struct hist_trigger_data *hist_data,
> hist_data->enable_timestamps = true;
> if (*flags & HIST_FIELD_FL_TIMESTAMP_USECS)
> hist_data->attrs->ts_in_usecs = true;
> - } else {
> + } else if (strcmp(field_name, "cpu") == 0)
> + *flags |= HIST_FIELD_FL_CPU;
> + else {
> field = trace_find_event_field(file->event_call, field_name);
> if (!field || !field->size) {
> field = ERR_PTR(-EINVAL);
> @@ -4612,6 +4636,8 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
>
> if (hist_field->flags & HIST_FIELD_FL_TIMESTAMP)
> seq_puts(m, "$common_timestamp");
> + else if (hist_field->flags & HIST_FIELD_FL_CPU)
> + seq_puts(m, "cpu");
> else if (field_name) {
> if (hist_field->flags & HIST_FIELD_FL_VAR_REF)
> seq_putc(m, '$');
> --
> 1.9.3
>