linux/kernel/trace/trace_irqsoff.c
Steven Rostedt 745b1626dd trace: set max latency variable to zero on default
Impact: trace max latencies on start of latency tracing

This patch sets the max latency to zero whenever one of the
irq variant tracers or the wakeup tracer is set to current tracer.

Most developers expect to see output when starting up a latency
tracer. But since the max_latency is already set to max, and
it takes a latency greater than max_latency to be recorded, there
is no trace. This is not the expected behavior and has even confused
myself.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-16 12:18:09 +01:00

513 lines
11 KiB
C

/*
* trace irqs off criticall timings
*
* Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
* Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
*
* From code in the latency_tracer, that is:
*
* Copyright (C) 2004-2006 Ingo Molnar
* Copyright (C) 2004 William Lee Irwin III
*/
#include <linux/kallsyms.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/ftrace.h>
#include <linux/fs.h>
#include "trace.h"
static struct trace_array *irqsoff_trace __read_mostly;
static int tracer_enabled __read_mostly;
static DEFINE_PER_CPU(int, tracing_cpu);
static DEFINE_SPINLOCK(max_trace_lock);
enum {
TRACER_IRQS_OFF = (1 << 1),
TRACER_PREEMPT_OFF = (1 << 2),
};
static int trace_type __read_mostly;
#ifdef CONFIG_PREEMPT_TRACER
static inline int
preempt_trace(void)
{
return ((trace_type & TRACER_PREEMPT_OFF) && preempt_count());
}
#else
# define preempt_trace() (0)
#endif
#ifdef CONFIG_IRQSOFF_TRACER
static inline int
irq_trace(void)
{
return ((trace_type & TRACER_IRQS_OFF) &&
irqs_disabled());
}
#else
# define irq_trace() (0)
#endif
/*
* Sequence count - we record it when starting a measurement and
* skip the latency if the sequence has changed - some other section
* did a maximum and could disturb our measurement with serial console
* printouts, etc. Truly coinciding maximum latencies should be rare
* and what happens together happens separately as well, so this doesnt
* decrease the validity of the maximum found:
*/
static __cacheline_aligned_in_smp unsigned long max_sequence;
#ifdef CONFIG_FUNCTION_TRACER
/*
* irqsoff uses its own tracer function to keep the overhead down:
*/
static void
irqsoff_tracer_call(unsigned long ip, unsigned long parent_ip)
{
struct trace_array *tr = irqsoff_trace;
struct trace_array_cpu *data;
unsigned long flags;
long disabled;
int cpu;
/*
* Does not matter if we preempt. We test the flags
* afterward, to see if irqs are disabled or not.
* If we preempt and get a false positive, the flags
* test will fail.
*/
cpu = raw_smp_processor_id();
if (likely(!per_cpu(tracing_cpu, cpu)))
return;
local_save_flags(flags);
/* slight chance to get a false positive on tracing_cpu */
if (!irqs_disabled_flags(flags))
return;
data = tr->data[cpu];
disabled = atomic_inc_return(&data->disabled);
if (likely(disabled == 1))
trace_function(tr, data, ip, parent_ip, flags, preempt_count());
atomic_dec(&data->disabled);
}
static struct ftrace_ops trace_ops __read_mostly =
{
.func = irqsoff_tracer_call,
};
#endif /* CONFIG_FUNCTION_TRACER */
/*
* Should this new latency be reported/recorded?
*/
static int report_latency(cycle_t delta)
{
if (tracing_thresh) {
if (delta < tracing_thresh)
return 0;
} else {
if (delta <= tracing_max_latency)
return 0;
}
return 1;
}
static void
check_critical_timing(struct trace_array *tr,
struct trace_array_cpu *data,
unsigned long parent_ip,
int cpu)
{
unsigned long latency, t0, t1;
cycle_t T0, T1, delta;
unsigned long flags;
int pc;
/*
* usecs conversion is slow so we try to delay the conversion
* as long as possible:
*/
T0 = data->preempt_timestamp;
T1 = ftrace_now(cpu);
delta = T1-T0;
local_save_flags(flags);
pc = preempt_count();
if (!report_latency(delta))
goto out;
spin_lock_irqsave(&max_trace_lock, flags);
/* check if we are still the max latency */
if (!report_latency(delta))
goto out_unlock;
trace_function(tr, data, CALLER_ADDR0, parent_ip, flags, pc);
latency = nsecs_to_usecs(delta);
if (data->critical_sequence != max_sequence)
goto out_unlock;
tracing_max_latency = delta;
t0 = nsecs_to_usecs(T0);
t1 = nsecs_to_usecs(T1);
data->critical_end = parent_ip;
update_max_tr_single(tr, current, cpu);
max_sequence++;
out_unlock:
spin_unlock_irqrestore(&max_trace_lock, flags);
out:
data->critical_sequence = max_sequence;
data->preempt_timestamp = ftrace_now(cpu);
tracing_reset(tr, cpu);
trace_function(tr, data, CALLER_ADDR0, parent_ip, flags, pc);
}
static inline void
start_critical_timing(unsigned long ip, unsigned long parent_ip)
{
int cpu;
struct trace_array *tr = irqsoff_trace;
struct trace_array_cpu *data;
unsigned long flags;
if (likely(!tracer_enabled))
return;
cpu = raw_smp_processor_id();
if (per_cpu(tracing_cpu, cpu))
return;
data = tr->data[cpu];
if (unlikely(!data) || atomic_read(&data->disabled))
return;
atomic_inc(&data->disabled);
data->critical_sequence = max_sequence;
data->preempt_timestamp = ftrace_now(cpu);
data->critical_start = parent_ip ? : ip;
tracing_reset(tr, cpu);
local_save_flags(flags);
trace_function(tr, data, ip, parent_ip, flags, preempt_count());
per_cpu(tracing_cpu, cpu) = 1;
atomic_dec(&data->disabled);
}
static inline void
stop_critical_timing(unsigned long ip, unsigned long parent_ip)
{
int cpu;
struct trace_array *tr = irqsoff_trace;
struct trace_array_cpu *data;
unsigned long flags;
cpu = raw_smp_processor_id();
/* Always clear the tracing cpu on stopping the trace */
if (unlikely(per_cpu(tracing_cpu, cpu)))
per_cpu(tracing_cpu, cpu) = 0;
else
return;
if (!tracer_enabled)
return;
data = tr->data[cpu];
if (unlikely(!data) ||
!data->critical_start || atomic_read(&data->disabled))
return;
atomic_inc(&data->disabled);
local_save_flags(flags);
trace_function(tr, data, ip, parent_ip, flags, preempt_count());
check_critical_timing(tr, data, parent_ip ? : ip, cpu);
data->critical_start = 0;
atomic_dec(&data->disabled);
}
/* start and stop critical timings used to for stoppage (in idle) */
void start_critical_timings(void)
{
if (preempt_trace() || irq_trace())
start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
}
EXPORT_SYMBOL_GPL(start_critical_timings);
void stop_critical_timings(void)
{
if (preempt_trace() || irq_trace())
stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
}
EXPORT_SYMBOL_GPL(stop_critical_timings);
#ifdef CONFIG_IRQSOFF_TRACER
#ifdef CONFIG_PROVE_LOCKING
void time_hardirqs_on(unsigned long a0, unsigned long a1)
{
if (!preempt_trace() && irq_trace())
stop_critical_timing(a0, a1);
}
void time_hardirqs_off(unsigned long a0, unsigned long a1)
{
if (!preempt_trace() && irq_trace())
start_critical_timing(a0, a1);
}
#else /* !CONFIG_PROVE_LOCKING */
/*
* Stubs:
*/
void early_boot_irqs_off(void)
{
}
void early_boot_irqs_on(void)
{
}
void trace_softirqs_on(unsigned long ip)
{
}
void trace_softirqs_off(unsigned long ip)
{
}
inline void print_irqtrace_events(struct task_struct *curr)
{
}
/*
* We are only interested in hardirq on/off events:
*/
void trace_hardirqs_on(void)
{
if (!preempt_trace() && irq_trace())
stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
}
EXPORT_SYMBOL(trace_hardirqs_on);
void trace_hardirqs_off(void)
{
if (!preempt_trace() && irq_trace())
start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
}
EXPORT_SYMBOL(trace_hardirqs_off);
void trace_hardirqs_on_caller(unsigned long caller_addr)
{
if (!preempt_trace() && irq_trace())
stop_critical_timing(CALLER_ADDR0, caller_addr);
}
EXPORT_SYMBOL(trace_hardirqs_on_caller);
void trace_hardirqs_off_caller(unsigned long caller_addr)
{
if (!preempt_trace() && irq_trace())
start_critical_timing(CALLER_ADDR0, caller_addr);
}
EXPORT_SYMBOL(trace_hardirqs_off_caller);
#endif /* CONFIG_PROVE_LOCKING */
#endif /* CONFIG_IRQSOFF_TRACER */
#ifdef CONFIG_PREEMPT_TRACER
void trace_preempt_on(unsigned long a0, unsigned long a1)
{
if (preempt_trace())
stop_critical_timing(a0, a1);
}
void trace_preempt_off(unsigned long a0, unsigned long a1)
{
if (preempt_trace())
start_critical_timing(a0, a1);
}
#endif /* CONFIG_PREEMPT_TRACER */
/*
* save_tracer_enabled is used to save the state of the tracer_enabled
* variable when we disable it when we open a trace output file.
*/
static int save_tracer_enabled;
static void start_irqsoff_tracer(struct trace_array *tr)
{
register_ftrace_function(&trace_ops);
if (tracing_is_enabled()) {
tracer_enabled = 1;
save_tracer_enabled = 1;
} else {
tracer_enabled = 0;
save_tracer_enabled = 0;
}
}
static void stop_irqsoff_tracer(struct trace_array *tr)
{
tracer_enabled = 0;
save_tracer_enabled = 0;
unregister_ftrace_function(&trace_ops);
}
static void __irqsoff_tracer_init(struct trace_array *tr)
{
tracing_max_latency = 0;
irqsoff_trace = tr;
/* make sure that the tracer is visible */
smp_wmb();
start_irqsoff_tracer(tr);
}
static void irqsoff_tracer_reset(struct trace_array *tr)
{
stop_irqsoff_tracer(tr);
}
static void irqsoff_tracer_start(struct trace_array *tr)
{
tracer_enabled = 1;
save_tracer_enabled = 1;
}
static void irqsoff_tracer_stop(struct trace_array *tr)
{
tracer_enabled = 0;
save_tracer_enabled = 0;
}
static void irqsoff_tracer_open(struct trace_iterator *iter)
{
/* stop the trace while dumping */
tracer_enabled = 0;
}
static void irqsoff_tracer_close(struct trace_iterator *iter)
{
/* restart tracing */
tracer_enabled = save_tracer_enabled;
}
#ifdef CONFIG_IRQSOFF_TRACER
static int irqsoff_tracer_init(struct trace_array *tr)
{
trace_type = TRACER_IRQS_OFF;
__irqsoff_tracer_init(tr);
return 0;
}
static struct tracer irqsoff_tracer __read_mostly =
{
.name = "irqsoff",
.init = irqsoff_tracer_init,
.reset = irqsoff_tracer_reset,
.start = irqsoff_tracer_start,
.stop = irqsoff_tracer_stop,
.open = irqsoff_tracer_open,
.close = irqsoff_tracer_close,
.print_max = 1,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_irqsoff,
#endif
};
# define register_irqsoff(trace) register_tracer(&trace)
#else
# define register_irqsoff(trace) do { } while (0)
#endif
#ifdef CONFIG_PREEMPT_TRACER
static int preemptoff_tracer_init(struct trace_array *tr)
{
trace_type = TRACER_PREEMPT_OFF;
__irqsoff_tracer_init(tr);
return 0;
}
static struct tracer preemptoff_tracer __read_mostly =
{
.name = "preemptoff",
.init = preemptoff_tracer_init,
.reset = irqsoff_tracer_reset,
.start = irqsoff_tracer_start,
.stop = irqsoff_tracer_stop,
.open = irqsoff_tracer_open,
.close = irqsoff_tracer_close,
.print_max = 1,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_preemptoff,
#endif
};
# define register_preemptoff(trace) register_tracer(&trace)
#else
# define register_preemptoff(trace) do { } while (0)
#endif
#if defined(CONFIG_IRQSOFF_TRACER) && \
defined(CONFIG_PREEMPT_TRACER)
static int preemptirqsoff_tracer_init(struct trace_array *tr)
{
trace_type = TRACER_IRQS_OFF | TRACER_PREEMPT_OFF;
__irqsoff_tracer_init(tr);
return 0;
}
static struct tracer preemptirqsoff_tracer __read_mostly =
{
.name = "preemptirqsoff",
.init = preemptirqsoff_tracer_init,
.reset = irqsoff_tracer_reset,
.start = irqsoff_tracer_start,
.stop = irqsoff_tracer_stop,
.open = irqsoff_tracer_open,
.close = irqsoff_tracer_close,
.print_max = 1,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_preemptirqsoff,
#endif
};
# define register_preemptirqsoff(trace) register_tracer(&trace)
#else
# define register_preemptirqsoff(trace) do { } while (0)
#endif
__init static int init_irqsoff_tracer(void)
{
register_irqsoff(irqsoff_tracer);
register_preemptoff(preemptoff_tracer);
register_preemptirqsoff(preemptirqsoff_tracer);
return 0;
}
device_initcall(init_irqsoff_tracer);