[PATCH v2 3/3] trace: emit tracepoint in preempt and irqs off tracer

Mathieu Desnoyers
2015-11-02T22:43:53Z

Allow Ftrace, Perf, and LTTng to hook on the irqsoff tracer and trace
irqsoff and preemptoff critical sections.

How to setup the irqsoff tracer for this use-case (needed for use with
Ftrace, Perf, or LTTng): if the tracing_thresh value is set, all
durations beyond the specified threshold will emit a
"core_critical_timing_hit" tracepoint. If unset, then the max duration
will be tracked. The current max duration can be reset using the
tracing_max_latency file.

echo 0 > /sys/kernel/debug/tracing/options/function-trace # don't need function tracing
echo 0 > /sys/kernel/debug/tracing/options/ftrace-buffer
echo preemptirqsoff > /sys/kernel/debug/tracing/current_tracer
echo 2 > /sys/kernel/debug/tracing/tracing_thresh # set threshold (e.g. 2 µs)
echo 1 > /sys/kernel/debug/tracing/tracing_on

The following two commands can also be useful to tweak the
irqsoff tracer:
echo 0 > /sys/kernel/debug/tracing/tracing_max_latency # reset max latency
echo 0 > /sys/kernel/debug/tracing/tracing_thresh # disable threshold

*** An example usage of Ftrace hooking on this tracepoint: ***

echo 1 > /sys/kernel/debug/tracing/events/core/core_critical_timing_hit/enable
cat /sys/kernel/debug/tracing/trace_pipe
[...]
bash-2380 19d..3 52794942us : core_critical_timing_hit: ip=0xffffffff811021de parent_ip=0xffffffff818d1b17 delta_ns=3402 irqs_disabled=0 preempt_disabled=1 in_softirq=0 in_irq=0 in_nmi=0

*** An example usage of Perf hooking on this tracepoint: ***

perf record -g -e core:core_critical_timing_hit -c 1 sleep 30
perf report -g

+ 100.00% 100.00% sleep [kernel.vmlinux] [k] check_critical_timing
+ 92.75% 0.00% sleep [kernel.vmlinux] [k] preempt_count_sub
+ 92.75% 0.00% sleep [kernel.vmlinux] [k] trace_preempt_on
+ 65.22% 0.00% sleep [kernel.vmlinux] [k] page_fault
+ 65.22% 0.00% sleep [kernel.vmlinux] [k] do_page_fault
+ 63.77% 0.00% sleep [kernel.vmlinux] [k] __do_page_fault
+ 63.77% 0.00% sleep [kernel.vmlinux] [k] handle_mm_fault
+ 56.52% 0.00% sleep [kernel.vmlinux] [k] _raw_spin_unlock
+ 30.43% 0.00% sleep ld-2.19.so [.] _dl_sysdep_start
[...]

*** An example usage of LTTng hooking on this tracepoint: ***

(as root)
lttng-sessiond -d

(then, as root or tracing group)
lttng create --live
lttng enable-event -k core_critical_timing_hit
lttng start
lttng view
[...]
[17:34:17.090669588] (+1.569689755) compudjdev core_critical_timing_hit: { cpu_id = 3 }, { ip = 0xFFFFFFFF81102135, parent_ip = 0xFFFFFFFFA0798E13, delta_ns = 252994, irqs_disabled = 0, preempt_disabled = 1, in_softirq = 0, in_irq = 0, in_nmi = 0 }

Tracepoints core_critical_timing_start and core_critical_timing_stop are
also available. They trigger at a much higher rate than
core_critical_timing_hit.

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>
---
Changes since v1:
- Remove unneeded tracepoint jump label bypass.
- Enhance TP_printk() formatting.
- Use new ftrace-buffer option in changelog.
- Add core_critical_timing_start/stop tracepoints.
---
include/trace/events/core.h | 96 ++++++++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_irqsoff.c | 17 ++++++--
2 files changed, 109 insertions(+), 4 deletions(-)
create mode 100644 include/trace/events/core.h

diff --git a/include/trace/events/core.h b/include/trace/events/core.h
new file mode 100644
index 0000000..ccc3430
--- /dev/null
+++ b/include/trace/events/core.h
@@ -0,0 +1,96 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM core
+
+#if !defined(_TRACE_CORE_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_CORE_H
+
+#include <linux/tracepoint.h>
+#include <linux/irqflags.h>
+#include <linux/preempt.h>
+
+/*
+ * Tracepoint for critical timings max/threshold hit.
+ */
+TRACE_EVENT(core_critical_timing_hit,
+
+ TP_PROTO(unsigned long ip, unsigned long parent_ip,
+ unsigned long flags, int preempt_cnt,
+ cycles_t delta_ns),
+
+ TP_ARGS(ip, parent_ip, flags, preempt_cnt, delta_ns),
+
+ TP_STRUCT__entry(
+ __field( unsigned long, ip )
+ __field( unsigned long, parent_ip )
+ __field( cycles_t, delta_ns )
+ __field( unsigned long, flags )
+ __field( int, preempt_cnt )
+ ),
+
+ TP_fast_assign(
+ __entry->ip = ip;
+ __entry->parent_ip = parent_ip;
+ __entry->delta_ns = delta_ns;
+ __entry->flags = flags;
+ __entry->preempt_cnt = preempt_cnt;
+ ),
+
+ TP_printk("ip=0x%lx parent_ip=0x%lx delta_ns=%llu irqs_disabled=%u preempt_disabled=%u in_softirq=%u in_irq=%u in_nmi=%u",
+ __entry->ip, __entry->parent_ip,
+ (unsigned long long) __entry->delta_ns,
+ !!raw_irqs_disabled_flags(__entry->flags),
+ !!(__entry->preempt_cnt & PREEMPT_MASK),
+ !!(__entry->preempt_cnt & SOFTIRQ_MASK),
+ !!(__entry->preempt_cnt & HARDIRQ_MASK),
+ !!(__entry->preempt_cnt & NMI_MASK))
+);
+
+/*
+ * Tracepoint for critical timings start/stop.
+ */
+DECLARE_EVENT_CLASS(core_critical_timing,
+
+ TP_PROTO(unsigned long ip, unsigned long parent_ip,
+ unsigned long flags, int preempt_cnt),
+
+ TP_ARGS(ip, parent_ip, flags, preempt_cnt),
+
+ TP_STRUCT__entry(
+ __field( unsigned long, ip )
+ __field( unsigned long, parent_ip )
+ __field( unsigned long, flags )
+ __field( int, preempt_cnt )
+ ),
+
+ TP_fast_assign(
+ __entry->ip = ip;
+ __entry->parent_ip = parent_ip;
+ __entry->flags = flags;
+ __entry->preempt_cnt = preempt_cnt;
+ ),
+
+ TP_printk("ip=0x%lx parent_ip=0x%lx irqs_disabled=%u preempt_disabled=%u in_softirq=%u in_irq=%u in_nmi=%u",
+ __entry->ip, __entry->parent_ip,
+ !!raw_irqs_disabled_flags(__entry->flags),
+ !!(__entry->preempt_cnt & PREEMPT_MASK),
+ !!(__entry->preempt_cnt & SOFTIRQ_MASK),
+ !!(__entry->preempt_cnt & HARDIRQ_MASK),
+ !!(__entry->preempt_cnt & NMI_MASK))
+);
+
+DEFINE_EVENT(core_critical_timing, core_critical_timing_start,
+ TP_PROTO(unsigned long ip, unsigned long parent_ip,
+ unsigned long flags, int preempt_cnt),
+ TP_ARGS(ip, parent_ip, flags, preempt_cnt)
+);
+
+DEFINE_EVENT(core_critical_timing, core_critical_timing_stop,
+ TP_PROTO(unsigned long ip, unsigned long parent_ip,
+ unsigned long flags, int preempt_cnt),
+ TP_ARGS(ip, parent_ip, flags, preempt_cnt)
+);
+
+#endif /* _TRACE_CORE_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 3e5635d..abfb77e 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -14,6 +14,9 @@
#include <linux/module.h>
#include <linux/ftrace.h>

+#define CREATE_TRACE_POINTS
+#include <trace/events/core.h>
+
#include "trace.h"

static struct trace_array *irqsoff_trace __read_mostly;
@@ -339,6 +342,8 @@ check_critical_timing(struct trace_array *tr,
/* Skip 5 functions to get to the irq/preempt enable function */
__trace_stack(tr, flags, 5, pc);
}
+ trace_core_critical_timing_hit(CALLER_ADDR0, parent_ip, flags, pc,
+ delta);

if (data->critical_sequence != max_sequence)
goto out_unlock;
@@ -365,7 +370,7 @@ out:
static inline void
start_critical_timing(unsigned long ip, unsigned long parent_ip)
{
- int cpu;
+ int cpu, pc;
struct trace_array *tr = irqsoff_trace;
struct trace_array_cpu *data;
unsigned long flags;
@@ -390,8 +395,10 @@ start_critical_timing(unsigned long ip, unsigned long parent_ip)
data->critical_start = parent_ip ? : ip;

local_save_flags(flags);
+ pc = preempt_count();
if (trace_flags & TRACE_ITER_FTRACE_BUFFER)
- __trace_function(tr, ip, parent_ip, flags, preempt_count());
+ __trace_function(tr, ip, parent_ip, flags, pc);
+ trace_core_critical_timing_start(ip, parent_ip, flags, pc);
per_cpu(tracing_cpu, cpu) = 1;

atomic_dec(&data->disabled);
@@ -400,7 +407,7 @@ start_critical_timing(unsigned long ip, unsigned long parent_ip)
static inline void
stop_critical_timing(unsigned long ip, unsigned long parent_ip)
{
- int cpu;
+ int cpu, pc;
struct trace_array *tr = irqsoff_trace;
struct trace_array_cpu *data;
unsigned long flags;
@@ -424,8 +431,10 @@ stop_critical_timing(unsigned long ip, unsigned long parent_ip)
atomic_inc(&data->disabled);

local_save_flags(flags);
+ pc = preempt_count();
if (trace_flags & TRACE_ITER_FTRACE_BUFFER)
- __trace_function(tr, ip, parent_ip, flags, preempt_count());
+ __trace_function(tr, ip, parent_ip, flags, pc);
+ trace_core_critical_timing_stop(ip, parent_ip, flags, pc);
check_critical_timing(tr, data, parent_ip ? : ip, cpu);
data->critical_start = 0;
atomic_dec(&data->disabled);
--
2.1.4