[RFC PATCH 2/2] trace: emit tracepoint in preempt and irqs off tracer
From: Mathieu Desnoyers
Date: Tue Oct 06 2015 - 20:02:23 EST
Allow Ftrace, Perf, and LTTng to hook on the irqsoff tracer and trace
longest irqsoff and preemptoff critical sections, or those beyond a
specified threshold.
This requires introducing a __trace_<name>() tracepoint static inline
which bypass static jump labels, because calling a breakpoint from the
irqsoff tracer triggers machine reboots due to recursive calls into the
tracer.
How to setup the irqsoff tracer for this use-case (needed for use with
Ftrace, Perf, or LTTng): if the tracing_thread value is set, all
durations beyond the specified threshold will emit a 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 preemptirqsoff > /sys/kernel/debug/tracing/current_tracer
echo 2 > /sys/kernel/debug/tracing/tracing_thresh # set threshold (e.g. 2 Âs)
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
[...]
cat-2422 1d..2 66157455us : core_critical_timing_hit: ip=0xffffffff81101cae parent_ip=0xffffffff818d38e7 delta_ns=5078 flags=6 preempt_cnt=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_*'
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 }
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
include/linux/tracepoint.h | 41 +++++++++++++++++++++++++++++-----
include/trace/events/core.h | 52 ++++++++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_irqsoff.c | 6 +++++
3 files changed, 94 insertions(+), 5 deletions(-)
create mode 100644 include/trace/events/core.h
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index c8e3030..17f5a47 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -95,6 +95,23 @@ extern void syscall_unregfunc(void);
#define TRACE_DEFINE_ENUM(x)
+#ifdef CONFIG_LOCKDEP
+static inline void check_trace_lockdep_rcu(struct tracepoint_func __rcu *funcs,
+ int condition)
+{
+ if (!condition)
+ return;
+ rcu_read_lock_sched_notrace();
+ rcu_dereference_sched(funcs);
+ rcu_read_unlock_sched_notrace();
+}
+#else
+static inline void check_trace_lockdep_rcu(struct tracepoint_func __rcu *funcs,
+ int condition)
+{
+}
+#endif
+
#endif /* _LINUX_TRACEPOINT_H */
/*
@@ -172,6 +189,11 @@ extern void syscall_unregfunc(void);
* instrumentation. This lets us find RCU issues triggered with tracepoints
* even when this tracepoint is off. This code has no purpose other than
* poking RCU a bit.
+ *
+ * trace_<name>() should usually be used for instrumentation.
+ *
+ * __trace_<name>() can be used in core instrumentation where recursion into
+ * the breakpoint handler is unwanted.
*/
#define __DECLARE_TRACE(name, proto, args, cond, data_proto, data_args) \
extern struct tracepoint __tracepoint_##name; \
@@ -182,11 +204,18 @@ extern void syscall_unregfunc(void);
TP_PROTO(data_proto), \
TP_ARGS(data_args), \
TP_CONDITION(cond),,); \
- if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \
- rcu_read_lock_sched_notrace(); \
- rcu_dereference_sched(__tracepoint_##name.funcs);\
- rcu_read_unlock_sched_notrace(); \
- } \
+ check_trace_lockdep_rcu(__tracepoint_##name.funcs, \
+ TP_CONDITION(cond)); \
+ } \
+ static inline void __trace_##name(proto) \
+ { \
+ if (static_key_enabled(&__tracepoint_##name.key)) \
+ __DO_TRACE(&__tracepoint_##name, \
+ TP_PROTO(data_proto), \
+ TP_ARGS(data_args), \
+ TP_CONDITION(cond),,); \
+ check_trace_lockdep_rcu(__tracepoint_##name.funcs, \
+ TP_CONDITION(cond)); \
} \
__DECLARE_TRACE_RCU(name, PARAMS(proto), PARAMS(args), \
PARAMS(cond), PARAMS(data_proto), PARAMS(data_args)) \
@@ -239,6 +268,8 @@ extern void syscall_unregfunc(void);
#define __DECLARE_TRACE(name, proto, args, cond, data_proto, data_args) \
static inline void trace_##name(proto) \
{ } \
+ static inline void __trace_##name(proto) \
+ { } \
static inline void trace_##name##_rcuidle(proto) \
{ } \
static inline int \
diff --git a/include/trace/events/core.h b/include/trace/events/core.h
new file mode 100644
index 0000000..b2c130c
--- /dev/null
+++ b/include/trace/events/core.h
@@ -0,0 +1,52 @@
+#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>
+
+/*
+ * Tracepoint for critical timings.
+ */
+DECLARE_EVENT_CLASS(core_critical_timing,
+
+ 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 flags=%lu preempt_cnt=%d",
+ __entry->ip, __entry->parent_ip,
+ (unsigned long long) __entry->delta_ns,
+ __entry->flags, __entry->preempt_cnt)
+);
+
+DEFINE_EVENT(core_critical_timing, 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)
+);
+
+#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 8523ea3..fad8949 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;
@@ -338,6 +341,9 @@ 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;
--
2.1.4
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