Sorry for the late reply.
On Tue, 19 Jan 2021 17:43:43 +0100
Viktor Rosendahl <viktor.rosend...@bmw.de> wrote:
> Eaerlier, tracing was disabled when reading the trace file. This behavior
> was changed with:
>
> commit 06e0a548bad0 ("tracing: Do not disable tracing when reading the
> trace file").
>
> This doesn't seem to work with the latency tracers.
>
> The above mentioned commit dit not only change the behavior but also added
> an option to emulate the old behavior. The idea with this patch is to
> enable this pause-on-trace option when the latency tracers are used.
>
> This is a workaround, perhaps it would be better to make the latency
> tracers work without pausing but I am not sure how to do that, or even
> how feasible it is without significant rework.
I think this is a fine workaround. The latency tracers are rather "special"
and some options just don't make sense for them. There's some things I wish
I had done different with them, but we can't fix because of backward
compatibility reasons.
I'll take a look at these today. Thanks.
-- Steve
>
> Signed-off-by: Viktor Rosendahl <viktor.rosend...@bmw.de>
> ---
> kernel/trace/trace_irqsoff.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
> index d06aab4dcbb8..6756379b661f 100644
> --- a/kernel/trace/trace_irqsoff.c
> +++ b/kernel/trace/trace_irqsoff.c
> @@ -562,6 +562,8 @@ static int __irqsoff_tracer_init(struct trace_array *tr)
> /* non overwrite screws up the latency tracers */
> set_tracer_flag(tr, TRACE_ITER_OVERWRITE, 1);
> set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, 1);
> + /* without pause, we will produce garbage if another latency occurs */
> + set_tracer_flag(tr, TRACE_ITER_PAUSE_ON_TRACE, 1);
>
> tr->max_latency = 0;
> irqsoff_trace = tr;
> @@ -583,11 +585,13 @@ static void __irqsoff_tracer_reset(struct trace_array
> *tr)
> {
> int lat_flag = save_flags & TRACE_ITER_LATENCY_FMT;
> int overwrite_flag = save_flags & TRACE_ITER_OVERWRITE;
> + int pause_flag = save_flags & TRACE_ITER_PAUSE_ON_TRACE;
>
> stop_irqsoff_tracer(tr, is_graph(tr));
>
> set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, lat_flag);
> set_tracer_flag(tr, TRACE_ITER_OVERWRITE, overwrite_flag);
> + set_tracer_flag(tr, TRACE_ITER_PAUSE_ON_TRACE, pause_flag);
> ftrace_reset_array_ops(tr);
>
> irqsoff_busy = false;
