linux-kernel - Re: [PATCH v4 06/37] ring-buffer: Redefine the unimplemented RINGBUF_TYPE_TIME

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Message-ID: <20171106050953.GA7557@sejong>
Date:   Mon, 6 Nov 2017 14:09:53 +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, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org, kernel-team@....com
Subject: Re: [PATCH v4 06/37] ring-buffer: Redefine the unimplemented
 RINGBUF_TYPE_TIME_STAMP

Hi Tom,

On Mon, Oct 30, 2017 at 03:51:48PM -0500, Tom Zanussi wrote:
> RINGBUF_TYPE_TIME_STAMP is defined but not used, and from what I can
> gather was reserved for something like an absolute timestamp feature
> for the ring buffer, if not a complete replacement of the current
> time_delta scheme.
> 
> This code redefines RINGBUF_TYPE_TIME_STAMP to implement absolute time
> stamps.  Another way to look at it is that it essentially forces
> extended time_deltas for all events.
> 
> The motivation for doing this is to enable time_deltas that aren't
> dependent on previous events in the ring buffer, making it feasible to
> use the ring_buffer_event timetamps in a more random-access way, for
> purposes other than serial event printing.
> 
> To set/reset this mode, use tracing_set_timestamp_abs() from the
> previous interface patch.
> 
> Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> ---

[SNIP]
> @@ -2220,13 +2246,16 @@ static void rb_inc_iter(struct ring_buffer_iter *iter)
>  }
>  
>  /* Slow path, do not inline */
> -static noinline struct ring_buffer_event *
> +static struct noinline ring_buffer_event *

struct noinline?  Looks like a mistake..

Thanks,
Namhyung


> -rb_add_time_stamp(struct ring_buffer_event *event, u64 delta)
> +rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
>  {
> -	event->type_len = RINGBUF_TYPE_TIME_EXTEND;
> +	if (abs)
> +		event->type_len = RINGBUF_TYPE_TIME_STAMP;
> +	else
> +		event->type_len = RINGBUF_TYPE_TIME_EXTEND;
>  
> -	/* Not the first event on the page? */
> -	if (rb_event_index(event)) {
> +	/* Not the first event on the page, or not delta? */
> +	if (abs || rb_event_index(event)) {
>  		event->time_delta = delta & TS_MASK;
>  		event->array[0] = delta >> TS_SHIFT;
>  	} else {