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

Tom Zanussi
2017-07-14T16:15:26Z

Hi Namhyung,

On Fri, 2017-07-14 at 14:25 +0900, Namhyung Kim wrote:
> 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?
>

Yes, I think you're right. Will take a closer look and change as
needed.

Thanks,

Tom