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Date:   Thu, 22 Jul 2021 22:29:24 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] tracing: Allow execnames to be passed as args for
 synthetic events

On Wed, 21 Jul 2021 21:47:02 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> Allow common_pid.execname to be saved in a variable in one histogram to be
> passed to another histogram that can pass it as a parameter to a synthetic
> event.
> 
>  ># echo 'hist:keys=pid:__arg__1=common_timestamp.usecs:arg2=common_pid.execname' \
>        > events/sched/sched_waking/trigger
>  ># echo 'wakeup_lat s32 pid; u64 delta; char wake_comm[]' > synthetic_events
>  ># echo 'hist:keys=next_pid:pid=next_pid,delta=common_timestamp.usecs-$__arg__1,exec=$arg2'\
> ':onmatch(sched.sched_waking).trace(wakeup_lat,$pid,$delta,$exec)' \
>  > events/sched/sched_switch/trigger
> 
> The above is a wake up latency synthetic event setup that passes the execname
> of the common_pid that woke the task to the scheduling of that task, which
> triggers a synthetic event that passes the original execname as a
> parameter to display it.
> 
>  ># echo 1 > events/synthetic/enable
>  ># cat trace
>     <idle>-0       [006] d..4   186.863801: wakeup_lat: pid=1306 delta=65 wake_comm=kworker/u16:3
>     <idle>-0       [000] d..4   186.863858: wakeup_lat: pid=163 delta=27 wake_comm=<idle>
>     <idle>-0       [001] d..4   186.863903: wakeup_lat: pid=1307 delta=36 wake_comm=kworker/u16:4
>     <idle>-0       [000] d..4   186.863927: wakeup_lat: pid=163 delta=5 wake_comm=<idle>
>     <idle>-0       [006] d..4   186.863957: wakeup_lat: pid=1306 delta=24 wake_comm=kworker/u16:3
>       sshd-1306    [006] d..4   186.864051: wakeup_lat: pid=61 delta=62 wake_comm=<idle>
>     <idle>-0       [000] d..4   186.965030: wakeup_lat: pid=609 delta=18 wake_comm=<idle>
>     <idle>-0       [006] d..4   186.987582: wakeup_lat: pid=1306 delta=65 wake_comm=kworker/u16:3
>     <idle>-0       [000] d..4   186.987639: wakeup_lat: pid=163 delta=27 wake_comm=<idle>
> 

This looks an interesting improvement. If we can do this, can we also filter
the event by 'comm' (or execname)? 

> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
> Changes since v1:
>   - Hit a bug on freeing the histogram, found that I used "char[]" for the
>     type, and it expects to be freed. Freed the old "type" and still use
>     "char[]" but have the normal freeing use kfree_const() on type.


BTW, if we can use this technic on the hist_field->type, we can cleanup 
other type = strdup("<any const type>", GFP_KERNEL) with type = "<any const type>" ?

Anyway, that will be done in another patch (I think that should be done first,
then we can avoid an odd kfree() in update_var_execname().)

Thank you,

> 
>  kernel/trace/trace_events_hist.c | 49 ++++++++++++++++++++++++++++----
>  1 file changed, 44 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 34325f41ebc0..bb1956efd5ef 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -1395,17 +1395,17 @@ static int hist_trigger_elt_data_alloc(struct tracing_map_elt *elt)
>  	struct hist_trigger_data *hist_data = elt->map->private_data;
>  	unsigned int size = TASK_COMM_LEN;
>  	struct hist_elt_data *elt_data;
> -	struct hist_field *key_field;
> +	struct hist_field *hist_field;
>  	unsigned int i, n_str;
>  
>  	elt_data = kzalloc(sizeof(*elt_data), GFP_KERNEL);
>  	if (!elt_data)
>  		return -ENOMEM;
>  
> -	for_each_hist_key_field(i, hist_data) {
> -		key_field = hist_data->fields[i];
> +	for_each_hist_field(i, hist_data) {
> +		hist_field = hist_data->fields[i];
>  
> -		if (key_field->flags & HIST_FIELD_FL_EXECNAME) {
> +		if (hist_field->flags & HIST_FIELD_FL_EXECNAME) {
>  			elt_data->comm = kzalloc(size, GFP_KERNEL);
>  			if (!elt_data->comm) {
>  				kfree(elt_data);
> @@ -1589,7 +1589,9 @@ static void __destroy_hist_field(struct hist_field *hist_field)
>  
>  	kfree(hist_field->var.name);
>  	kfree(hist_field->name);
> -	kfree(hist_field->type);
> +
> +	/* execname vars use a constant type */
> +	kfree_const(hist_field->type);
>  
>  	kfree(hist_field->system);
>  	kfree(hist_field->event_name);
> @@ -3707,6 +3709,40 @@ static int create_val_field(struct hist_trigger_data *hist_data,
>  	return __create_val_field(hist_data, val_idx, file, NULL, field_str, 0);
>  }
>  
> +static const char *no_comm = "(no comm)";
> +
> +static u64 hist_field_execname(struct hist_field *hist_field,
> +			       struct tracing_map_elt *elt,
> +			       struct trace_buffer *buffer,
> +			       struct ring_buffer_event *rbe,
> +			       void *event)
> +{
> +	struct hist_elt_data *elt_data;
> +
> +	if (WARN_ON_ONCE(!elt))
> +		return (u64)(unsigned long)no_comm;
> +
> +	elt_data = elt->private_data;
> +
> +	if (WARN_ON_ONCE(!elt_data->comm))
> +		return (u64)(unsigned long)no_comm;
> +
> +	return (u64)(unsigned long)(elt_data->comm);
> +}
> +
> +/* Convert a var that points to common_pid.execname to a string */
> +static void update_var_execname(struct hist_field *hist_field)
> +{
> +	hist_field->flags = HIST_FIELD_FL_STRING | HIST_FIELD_FL_VAR |
> +		HIST_FIELD_FL_EXECNAME;
> +	hist_field->size = MAX_FILTER_STR_VAL;
> +	hist_field->is_signed = 0;
> +	kfree(hist_field->type);
> +	/* This uses kfree_const() to free */
> +	hist_field->type = "char[]";
> +	hist_field->fn = hist_field_execname;
> +}
> +
>  static int create_var_field(struct hist_trigger_data *hist_data,
>  			    unsigned int val_idx,
>  			    struct trace_event_file *file,
> @@ -3731,6 +3767,9 @@ static int create_var_field(struct hist_trigger_data *hist_data,
>  
>  	ret = __create_val_field(hist_data, val_idx, file, var_name, expr_str, flags);
>  
> +	if (!ret && hist_data->fields[val_idx]->flags & HIST_FIELD_FL_EXECNAME)
> +		update_var_execname(hist_data->fields[val_idx]);
> +
>  	if (!ret && hist_data->fields[val_idx]->flags & HIST_FIELD_FL_STRING)
>  		hist_data->fields[val_idx]->var_str_idx = hist_data->n_var_str++;
>  
> -- 
> 2.31.1
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>

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