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

Namhyung Kim
2017-07-14T05:25:11Z

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@linux.intel.com>
> ---
> 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
>