Re: [PATCH v11 13/28] tracing: Add hist trigger support for pausing and continuing a trace

[Namhyung Kim <namhyung@kernel.org>]

On Thu, Oct 22, 2015 at 01:14:17PM -0500, Tom Zanussi wrote:
> Allow users to append 'pause' or 'continue' to an existing trigger in
> order to have it paused or to have a paused trace continue.
> 
> This expands the hist trigger syntax from this:
>     # echo hist:keys=xxx:vals=yyy:sort=zzz.descending \
>           [ if filter] > event/trigger
> 
> to this:
> 
>     # echo hist:keys=xxx:vals=yyy:sort=zzz.descending:pause or cont \
>           [ if filter] > event/trigger

What if 'cont' is used for a non-existing hist?  I think it should
fail with -ENOENT but it seems that it'd create a new hist trigger..

Thanks,
Namhyung


> 
> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
> Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> ---
>  kernel/trace/trace.c             |  7 ++++++-
>  kernel/trace/trace_events_hist.c | 26 +++++++++++++++++++++++---
>  2 files changed, 29 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index efa8d05..a223959 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3802,6 +3802,7 @@ static const char readme_msg[] =
>  	"\t            [:values=<field1[,field2,...]]\n"
>  	"\t            [:sort=field1,field2,...]\n"
>  	"\t            [:size=#entries]\n"
> +	"\t            [:pause][:continue]\n"
>  	"\t            [if <filter>]\n\n"
>  	"\t    When a matching event is hit, an entry is added to a hash\n"
>  	"\t    table using the key(s) and value(s) named, and the value of a\n"
> @@ -3816,7 +3817,11 @@ static const char readme_msg[] =
>  	"\t    used to specify more or fewer than the default 2048 entries\n"
>  	"\t    for the hashtable size.\n\n"
>  	"\t    Reading the 'hist' file for the event will dump the hash\n"
> -	"\t    table in its entirety to stdout."
> +	"\t    table in its entirety to stdout.\n\n"
> +	"\t    The 'pause' parameter can be used to pause an existing hist\n"
> +	"\t    trigger or to start a hist trigger but not log any events\n"
> +	"\t    until told to do so.  'continue' can be used to start or\n"
> +	"\t    restart a paused hist trigger.\n\n"
>  #endif
>  ;
>  
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 4fc3136..8753c3b 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -78,6 +78,8 @@ struct hist_trigger_attrs {
>  	char		*keys_str;
>  	char		*vals_str;
>  	char		*sort_key_str;
> +	bool		pause;
> +	bool		cont;
>  	unsigned int	map_bits;
>  };
>  
> @@ -184,6 +186,11 @@ static struct hist_trigger_attrs *parse_hist_trigger_attrs(char *trigger_str)
>  			attrs->vals_str = kstrdup(str, GFP_KERNEL);
>  		else if (!strncmp(str, "sort", strlen("sort")))
>  			attrs->sort_key_str = kstrdup(str, GFP_KERNEL);
> +		else if (!strncmp(str, "pause", strlen("pause")))
> +			attrs->pause = true;
> +		else if (!strncmp(str, "continue", strlen("continue")) ||
> +			 !strncmp(str, "cont", strlen("cont")))
> +			attrs->cont = true;
>  		else if (!strncmp(str, "size", strlen("size"))) {
>  			int map_bits = parse_map_size(str);
>  
> @@ -843,7 +850,10 @@ static int event_hist_trigger_print(struct seq_file *m,
>  	if (data->filter_str)
>  		seq_printf(m, " if %s", data->filter_str);
>  
> -	seq_puts(m, " [active]");
> +	if (data->paused)
> +		seq_puts(m, " [paused]");
> +	else
> +		seq_puts(m, " [active]");
>  
>  	seq_putc(m, '\n');
>  
> @@ -882,16 +892,25 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
>  				 struct event_trigger_data *data,
>  				 struct trace_event_file *file)
>  {
> +	struct hist_trigger_data *hist_data = data->private_data;
>  	struct event_trigger_data *test;
>  	int ret = 0;
>  
>  	list_for_each_entry_rcu(test, &file->triggers, list) {
>  		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
> -			ret = -EEXIST;
> +			if (hist_data->attrs->pause)
> +				test->paused = true;
> +			else if (hist_data->attrs->cont)
> +				test->paused = false;
> +			else
> +				ret = -EEXIST;
>  			goto out;
>  		}
>  	}
>  
> +	if (hist_data->attrs->pause)
> +		data->paused = true;
> +
>  	if (data->ops->init) {
>  		ret = data->ops->init(data->ops, data);
>  		if (ret < 0)
> @@ -984,7 +1003,8 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
>  	 * triggers registered a failure too.
>  	 */
>  	if (!ret) {
> -		ret = -ENOENT;
> +		if (!(attrs->pause || attrs->cont))
> +			ret = -ENOENT;
>  		goto out_free;
>  	} else if (ret < 0)
>  		goto out_free;
> -- 
> 1.9.3
>