Re: [PATCH 2/3] ftrace: add ftrace-buffer option

Steven Rostedt
2015-11-02T22:56:06Z

On Mon, 2 Nov 2015 17:42:43 -0500
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:

> In order to use ftrace tracers to generate tracepoints without doing
> tracing to its own hardcoded ring buffers, add a ftrace-buffer option
> (default: 1). When set to 0, it disables tracing into the ftrace
> hardcoded buffers.
>

This needs a more in depth change log. I have no idea why this is
needed.

Also, the trace_options code have been redesigned, and this won't apply
to it (see linux-next). Also, if this is only for irqsoff latency
tracers, it should be a tracer option, not a global one.

-- Steve

> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> CC: Thomas Gleixner <tglx@linutronix.de>
> CC: Steven Rostedt <rostedt@goodmis.org>
> CC: Ingo Molnar <mingo@redhat.com>
> CC: Peter Zijlstra <peterz@infradead.org>
> ---
> kernel/trace/trace.c | 4 +++-
> kernel/trace/trace.h | 1 +
> kernel/trace/trace_irqsoff.c | 19 +++++++++++--------
> 3 files changed, 15 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 6e79408..d664f0e 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -472,7 +472,8 @@ static inline void trace_access_lock_init(void)
> unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK |
> TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO | TRACE_ITER_SLEEP_TIME |
> TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE |
> - TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS | TRACE_ITER_FUNCTION;
> + TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS | TRACE_ITER_FUNCTION |
> + TRACE_ITER_FTRACE_BUFFER;
>
> static void tracer_tracing_on(struct trace_array *tr)
> {
> @@ -862,6 +863,7 @@ static const char *trace_options[] = {
> "irq-info",
> "markers",
> "function-trace",
> + "ftrace-buffer",
> NULL
> };
>
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 74bde81..29968e1 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -930,6 +930,7 @@ enum trace_iterator_flags {
> TRACE_ITER_IRQ_INFO = 0x800000,
> TRACE_ITER_MARKERS = 0x1000000,
> TRACE_ITER_FUNCTION = 0x2000000,
> + TRACE_ITER_FTRACE_BUFFER = 0x4000000,
> };
>
> /*
> diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
> index 8523ea3..3e5635d 100644
> --- a/kernel/trace/trace_irqsoff.c
> +++ b/kernel/trace/trace_irqsoff.c
> @@ -334,9 +334,11 @@ check_critical_timing(struct trace_array *tr,
> if (!report_latency(tr, delta))
> goto out_unlock;
>
> - __trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
> - /* Skip 5 functions to get to the irq/preempt enable function */
> - __trace_stack(tr, flags, 5, pc);
> + if (trace_flags & TRACE_ITER_FTRACE_BUFFER) {
> + __trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
> + /* Skip 5 functions to get to the irq/preempt enable function */
> + __trace_stack(tr, flags, 5, pc);
> + }
>
> if (data->critical_sequence != max_sequence)
> goto out_unlock;
> @@ -356,7 +358,8 @@ out_unlock:
> out:
> data->critical_sequence = max_sequence;
> data->preempt_timestamp = ftrace_now(cpu);
> - __trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
> + if (trace_flags & TRACE_ITER_FTRACE_BUFFER)
> + __trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
> }
>
> static inline void
> @@ -387,9 +390,8 @@ start_critical_timing(unsigned long ip, unsigned long parent_ip)
> data->critical_start = parent_ip ? : ip;
>
> local_save_flags(flags);
> -
> - __trace_function(tr, ip, parent_ip, flags, preempt_count());
> -
> + if (trace_flags & TRACE_ITER_FTRACE_BUFFER)
> + __trace_function(tr, ip, parent_ip, flags, preempt_count());
> per_cpu(tracing_cpu, cpu) = 1;
>
> atomic_dec(&data->disabled);
> @@ -422,7 +424,8 @@ stop_critical_timing(unsigned long ip, unsigned long parent_ip)
> atomic_inc(&data->disabled);
>
> local_save_flags(flags);
> - __trace_function(tr, ip, parent_ip, flags, preempt_count());
> + if (trace_flags & TRACE_ITER_FTRACE_BUFFER)
> + __trace_function(tr, ip, parent_ip, flags, preempt_count());
> check_critical_timing(tr, data, parent_ip ? : ip, cpu);
> data->critical_start = 0;
> atomic_dec(&data->disabled);