Re: [RFC] tracing: Add support for critical section event tracing

[Joel Fernandes]

Hi Steven,

Did you have any comments about this patch? It was sent a while ago
and if you can provide me your initial thoughts on it, I would
appreciate it. (Sorry to ping you about it during the busy merge
window time, but I was thinking if I can get any initial early
comments from you then I can get to work on it and finish in time well
before the next merge window).

Regards,
Joel

On Tue, Apr 11, 2017 at 10:38 PM, Joel Fernandes <joelaf@xxxxxxxxxx> wrote:
> Critical section trace events can be used for tracing the start and
> end of a critical section which can be used by a trace viewer like
> systrace to graphically view the start and end of a critical section and
> correlate them with latencies and scheduling issues.
>
> Reason for starting critical section:
> Either preemption or interrupts were turned off.
> Reason for ending critical section:
> Both preemption and interrupts are now turned back on.
>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Signed-off-by: Joel Fernandes <joelaf@xxxxxxxxxx>
> --
> Here's an example of how Android's systrace will be using it to show critical
> sections as a gantt chart: http://imgur.com/download/TZplEVp
> ---
>  include/trace/events/critical.h | 55 +++++++++++++++++++++++++++++++
>  kernel/trace/Kconfig            |  6 ++++
>  kernel/trace/trace_irqsoff.c    | 73 +++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 134 insertions(+)
>  create mode 100644 include/trace/events/critical.h
>
> diff --git a/include/trace/events/critical.h b/include/trace/events/critical.h
> new file mode 100644
> index 000000000000..bfd58dd4f48f
> --- /dev/null
> +++ b/include/trace/events/critical.h
> @@ -0,0 +1,55 @@
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM critical
> +
> +#if !defined(_TRACE_CRITICAL_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_CRITICAL_H
> +
> +#include <linux/ktime.h>
> +#include <linux/tracepoint.h>
> +#include <linux/string.h>
> +
> +TRACE_EVENT(critical_start,
> +
> +       TP_PROTO(unsigned long ip, unsigned long parent_ip),
> +
> +       TP_ARGS(ip, parent_ip),
> +
> +       TP_STRUCT__entry(
> +               __array(char, func, 16)
> +               __array(char, parent, 16)
> +       ),
> +
> +       TP_fast_assign(
> +               snprintf(__entry->func, 16, "%pf", (void *)ip);
> +               snprintf(__entry->parent, 16, "%pf", (void *)parent_ip);
> +       ),
> +
> +       TP_printk("caller=%s parent=%s\n",
> +                 __entry->func,
> +                 __entry->parent)
> +);
> +
> +TRACE_EVENT(critical_end,
> +
> +       TP_PROTO(unsigned long ip, unsigned long parent_ip),
> +
> +       TP_ARGS(ip, parent_ip),
> +
> +       TP_STRUCT__entry(
> +               __array(char, func, 16)
> +               __array(char, parent, 16)
> +       ),
> +
> +       TP_fast_assign(
> +               snprintf(__entry->func, 16, "%pf", (void *)ip);
> +               snprintf(__entry->parent, 16, "%pf", (void *)parent_ip);
> +       ),
> +
> +       TP_printk("caller=%s parent=%s\n",
> +                 __entry->func,
> +                 __entry->parent)
> +);
> +#endif /* _TRACE_CRITICAL_H */
> +
> +/* This part ust be outside protection */
> +#include <trace/define_trace.h>
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index d5038005eb5d..986a07985360 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -208,6 +208,12 @@ config PREEMPT_TRACER
>           enabled. This option and the irqs-off timing option can be
>           used together or separately.)
>
> +config TRACE_CRITICAL_SECTION_EVENTS
> +       bool "Trace critical sections as trace events"
> +       default n
> +       select IRQSOFF_TRACER
> +       select PREEMPT_TRACER
> +
>  config SCHED_TRACER
>         bool "Scheduling Latency Tracer"
>         select GENERIC_TRACER
> diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
> index 7758bc0617cb..a14ce6185885 100644
> --- a/kernel/trace/trace_irqsoff.c
> +++ b/kernel/trace/trace_irqsoff.c
> @@ -13,6 +13,8 @@
>  #include <linux/uaccess.h>
>  #include <linux/module.h>
>  #include <linux/ftrace.h>
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/critical.h>
>
>  #include "trace.h"
>
> @@ -20,6 +22,7 @@ static struct trace_array             *irqsoff_trace __read_mostly;
>  static int                             tracer_enabled __read_mostly;
>
>  static DEFINE_PER_CPU(int, tracing_cpu);
> +static DEFINE_PER_CPU(int, tracing_events_cpu);
>
>  static DEFINE_RAW_SPINLOCK(max_trace_lock);
>
> @@ -362,6 +365,44 @@ check_critical_timing(struct trace_array *tr,
>         __trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
>  }
>
> +#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
> +/*
> + * Called when either preempt or irq are turned off
> + */
> +static inline void
> +start_critical_event(unsigned long ip, unsigned long parent_ip)
> +{
> +       int cpu;
> +
> +       cpu = raw_smp_processor_id();
> +
> +       if (per_cpu(tracing_events_cpu, cpu))
> +               return;
> +
> +       trace_critical_start(ip, parent_ip);
> +
> +       per_cpu(tracing_events_cpu, cpu) = 1;
> +}
> +
> +/*
> + * Called when both preempt and irq are turned back on
> + */
> +static inline void
> +stop_critical_event(unsigned long ip, unsigned long parent_ip)
> +{
> +       int cpu;
> +
> +       cpu = raw_smp_processor_id();
> +
> +       if (unlikely(per_cpu(tracing_events_cpu, cpu)))
> +               per_cpu(tracing_events_cpu, cpu) = 0;
> +       else
> +               return;
> +
> +       trace_critical_end(ip, parent_ip);
> +}
> +#endif
> +
>  static inline void
>  start_critical_timing(unsigned long ip, unsigned long parent_ip)
>  {
> @@ -434,6 +475,10 @@ stop_critical_timing(unsigned long ip, unsigned long parent_ip)
>  /* start and stop critical timings used to for stoppage (in idle) */
>  void start_critical_timings(void)
>  {
> +#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
> +       if (irqs_disabled() || preempt_count())
> +               start_critical_event(CALLER_ADDR0, CALLER_ADDR1);
> +#endif
>         if (preempt_trace() || irq_trace())
>                 start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
>  }
> @@ -441,6 +486,10 @@ EXPORT_SYMBOL_GPL(start_critical_timings);
>
>  void stop_critical_timings(void)
>  {
> +#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
> +       if (irqs_disabled() || preempt_count())
> +               stop_critical_event(CALLER_ADDR0, CALLER_ADDR1);
> +#endif
>         if (preempt_trace() || irq_trace())
>                 stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
>  }
> @@ -483,6 +532,10 @@ inline void print_irqtrace_events(struct task_struct *curr)
>   */
>  void trace_hardirqs_on(void)
>  {
> +#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
> +       if (!preempt_count())
> +               stop_critical_event(CALLER_ADDR0, CALLER_ADDR1);
> +#endif
>         if (!preempt_trace() && irq_trace())
>                 stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
>  }
> @@ -490,6 +543,10 @@ EXPORT_SYMBOL(trace_hardirqs_on);
>
>  void trace_hardirqs_off(void)
>  {
> +#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
> +       if (!preempt_count())
> +               start_critical_event(CALLER_ADDR0, CALLER_ADDR1);
> +#endif
>         if (!preempt_trace() && irq_trace())
>                 start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
>  }
> @@ -497,6 +554,10 @@ EXPORT_SYMBOL(trace_hardirqs_off);
>
>  __visible void trace_hardirqs_on_caller(unsigned long caller_addr)
>  {
> +#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
> +       if (!preempt_count())
> +               stop_critical_event(CALLER_ADDR0, caller_addr);
> +#endif
>         if (!preempt_trace() && irq_trace())
>                 stop_critical_timing(CALLER_ADDR0, caller_addr);
>  }
> @@ -504,6 +565,10 @@ EXPORT_SYMBOL(trace_hardirqs_on_caller);
>
>  __visible void trace_hardirqs_off_caller(unsigned long caller_addr)
>  {
> +#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
> +       if (!preempt_count())
> +               start_critical_event(CALLER_ADDR0, caller_addr);
> +#endif
>         if (!preempt_trace() && irq_trace())
>                 start_critical_timing(CALLER_ADDR0, caller_addr);
>  }
> @@ -515,12 +580,20 @@ EXPORT_SYMBOL(trace_hardirqs_off_caller);
>  #ifdef CONFIG_PREEMPT_TRACER
>  void trace_preempt_on(unsigned long a0, unsigned long a1)
>  {
> +#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
> +       if (!irqs_disabled())
> +               stop_critical_event(a0, a1);
> +#endif
>         if (preempt_trace() && !irq_trace())
>                 stop_critical_timing(a0, a1);
>  }
>
>  void trace_preempt_off(unsigned long a0, unsigned long a1)
>  {
> +#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
> +       if (!irqs_disabled())
> +               start_critical_event(a0, a1);
> +#endif
>         if (preempt_trace() && !irq_trace())
>                 start_critical_timing(a0, a1);
>  }
> --
> 2.12.2.715.g7642488e1d-goog
>