Re: [PATCH v3 26/33] tracing: Add cpu field for hist triggers

[Steven Rostedt]

On Fri, 22 Sep 2017 15:00:06 -0500
Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx> 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 $common_cpu because 'cpu' already exists as a special
> filter field and it makes more sense to match that rather than add
> another name for the same thing.
> 
> Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
> ---
>  Documentation/trace/events.txt   | 18 ++++++++++++++++++
>  kernel/trace/trace_events_hist.c | 28 +++++++++++++++++++++++++++-
>  2 files changed, 45 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt
> index 2cc08d4..f36fa00 100644
> --- a/Documentation/trace/events.txt
> +++ b/Documentation/trace/events.txt
> @@ -668,6 +668,24 @@ The following commands are supported:
>    The examples below provide a more concrete illustration of the
>    concepts and typical usage patterns discussed above.
>  
> +  'special' event fields
> +  ------------------------
> +
> +  There are a number of 'special event fields' available for use as
> +  keys or values in a hist trigger.  These look like and behave as if
> +  they were actual event fields, but aren't really part of the event's
> +  field definition or format file.  They are however available for any
> +  event, and can be used anywhere an actual event field could be.
> +  'Special' field names are always prefixed with a '$' character to
> +  indicate that they're not normal fields (with the exception of
> +  'cpu', for compatibility with existing filter usage):
> +
> +    $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.
> +
>

You were going to update this too.

-- Steve