linux-kernel - Re: [PATCH v7 15/37] tracing: Add variable support to hist triggers

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Date:   Fri, 8 Dec 2017 22:02:24 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc:     rostedt@...dmis.org, tglx@...utronix.de, mhiramat@...nel.org,
        vedang.patel@...el.com, bigeasy@...utronix.de,
        joel.opensrc@...il.com, joelaf@...gle.com,
        mathieu.desnoyers@...icios.com, baohong.liu@...el.com,
        rajvi.jingar@...el.com, julia@...com, fengguang.wu@...el.com,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
        kernel-team@....com
Subject: Re: [PATCH v7 15/37] tracing: Add variable support to hist triggers

Hi Tom,

On Wed, Dec 06, 2017 at 04:37:56PM -0600, Tom Zanussi wrote:
> Add support for saving the value of a current event's event field by
> assigning it to a variable that can be read by a subsequent event.
> 
> The basic syntax for saving a variable is to simply prefix a unique
> variable name not corresponding to any keyword along with an '=' sign
> to any event field.
> 
> Both keys and values can be saved and retrieved in this way:
> 
>     # echo 'hist:keys=next_pid:vals=$ts0:ts0=common_timestamp ...
>     # echo 'hist:timer_pid=common_pid:key=$timer_pid ...'
> 
> If a variable isn't a key variable or prefixed with 'vals=', the
> associated event field will be saved in a variable but won't be summed
> as a value:
> 
>     # echo 'hist:keys=next_pid:ts1=common_timestamp:...
> 
> Multiple variables can be assigned at the same time:
> 
>     # echo 'hist:keys=pid:vals=$ts0,$b,field2:ts0=common_timestamp,b=field1 ...
> 
> Multiple (or single) variables can also be assigned at the same time
> using separate assignments:
> 
>     # echo 'hist:keys=pid:vals=$ts0:ts0=common_timestamp:b=field1:c=field2 ...
> 
> Variables set as above can be used by being referenced from another
> event, as described in a subsequent patch.
> 
> Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> Signed-off-by: Baohong Liu <baohong.liu@...el.com>
> ---

[SNIP]
> @@ -962,14 +1201,28 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
>  				    struct ring_buffer_event *rbe)
>  {
>  	struct hist_field *hist_field;
> -	unsigned int i;
> +	unsigned int i, var_idx;
>  	u64 hist_val;
>  
>  	for_each_hist_val_field(i, hist_data) {
>  		hist_field = hist_data->fields[i];
> -		hist_val = hist_field->fn(hist_field, rec, rbe);
> +		hist_val = hist_field->fn(hist_field, rbe, rec);

Why is this changed?


> +		if (hist_field->flags & HIST_FIELD_FL_VAR) {
> +			var_idx = hist_field->var.idx;
> +			tracing_map_set_var(elt, var_idx, hist_val);
> +			continue;
> +		}
>  		tracing_map_update_sum(elt, i, hist_val);
>  	}
> +
> +	for_each_hist_key_field(i, hist_data) {
> +		hist_field = hist_data->fields[i];
> +		if (hist_field->flags & HIST_FIELD_FL_VAR) {
> +			hist_val = hist_field->fn(hist_field, rbe, rec);

Also it seems to have a wrong argument order.

Thanks,
Namhyung


> +			var_idx = hist_field->var.idx;
> +			tracing_map_set_var(elt, var_idx, hist_val);
> +		}
> +	}
>  }