Re: [PATCH 03/32] ring-buffer: Add interface for setting absolute time stamps

[Namhyung Kim]

On Mon, Jun 26, 2017 at 05:49:04PM -0500, Tom Zanussi wrote:
> Define a new function, tracing_set_time_stamp_abs(), which can be used
> to enable or disable the use of absolute timestamps rather than time
> deltas for a trace array.
> 
> This resets the buffer to prevent a mix of time deltas and absolute
> timestamps.
> 
> Only the interface is added here; a subsequent patch will add the
> underlying implementation.
> 
> Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
> ---
>  include/linux/ring_buffer.h |  2 ++
>  kernel/trace/ring_buffer.c  | 11 +++++++++++
>  kernel/trace/trace.c        | 25 ++++++++++++++++++++++++-
>  kernel/trace/trace.h        |  2 ++
>  4 files changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
> index ee9b461..28e3472 100644
> --- a/include/linux/ring_buffer.h
> +++ b/include/linux/ring_buffer.h
> @@ -180,6 +180,8 @@ void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
>  				      int cpu, u64 *ts);
>  void ring_buffer_set_clock(struct ring_buffer *buffer,
>  			   u64 (*clock)(void));
> +void ring_buffer_set_time_stamp_abs(struct ring_buffer *buffer, bool abs);
> +bool ring_buffer_time_stamp_abs(struct ring_buffer *buffer);
>  
>  size_t ring_buffer_page_len(void *page);
>  
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 4ae268e..f544738 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -485,6 +485,7 @@ struct ring_buffer {
>  	u64				(*clock)(void);
>  
>  	struct rb_irq_work		irq_work;
> +	bool				time_stamp_abs;
>  };
>  
>  struct ring_buffer_iter {
> @@ -1379,6 +1380,16 @@ void ring_buffer_set_clock(struct ring_buffer *buffer,
>  	buffer->clock = clock;
>  }
>  
> +void ring_buffer_set_time_stamp_abs(struct ring_buffer *buffer, bool abs)
> +{
> +	buffer->time_stamp_abs = abs;
> +}
> +
> +bool ring_buffer_time_stamp_abs(struct ring_buffer *buffer)
> +{
> +	return buffer->time_stamp_abs;
> +}
> +
>  static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
>  
>  static inline unsigned long rb_page_entries(struct buffer_page *bpage)
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 19ac208..da8cd51 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2169,7 +2169,7 @@ struct ring_buffer_event *
>  
>  	*current_rb = trace_file->tr->trace_buffer.buffer;
>  
> -	if ((trace_file->flags &
> +	if (!ring_buffer_time_stamp_abs(*current_rb) && (trace_file->flags &
>  	     (EVENT_FILE_FL_SOFT_DISABLED | EVENT_FILE_FL_FILTERED)) &&
>  	    (entry = this_cpu_read(trace_buffered_event))) {
>  		/* Try to use the per cpu buffer first */
> @@ -6079,6 +6079,29 @@ static int tracing_clock_open(struct inode *inode, struct file *file)
>  	return ret;
>  }
>  
> +int tracing_set_time_stamp_abs(struct trace_array *tr, bool abs)
> +{
> +	mutex_lock(&trace_types_lock);
> +
> +	ring_buffer_set_time_stamp_abs(tr->trace_buffer.buffer, abs);
> +
> +	/*
> +	 * New timestamps may not be consistent with the previous setting.
> +	 * Reset the buffer so that it doesn't have incomparable timestamps.
> +	 */
> +	tracing_reset_online_cpus(&tr->trace_buffer);
> +
> +#ifdef CONFIG_TRACER_MAX_TRACE
> +	if (tr->flags & TRACE_ARRAY_FL_GLOBAL && tr->max_buffer.buffer)
> +		ring_buffer_set_time_stamp_abs(tr->max_buffer.buffer, abs);
> +	tracing_reset_online_cpus(&tr->max_buffer);

Why do you do this only for the global array?  AFAIK instance arrays
can have the max buffer too.  Am I missing something?

Thanks,
Namhyung


> +#endif
> +
> +	mutex_unlock(&trace_types_lock);
> +
> +	return 0;
> +}
> +
>  struct ftrace_buffer_info {
>  	struct trace_iterator	iter;
>  	void			*spare;
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 69a3ab3..155ad9a 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -281,6 +281,8 @@ enum {
>  extern int trace_array_get(struct trace_array *tr);
>  extern void trace_array_put(struct trace_array *tr);
>  
> +extern int tracing_set_time_stamp_abs(struct trace_array *tr, bool abs);
> +
>  /*
>   * The global tracer (top) should be the first trace array added,
>   * but we check the flag anyway.
> -- 
> 1.9.3
>