[PATCH 20/23 -v8] trace preempt off critical timings

From: Steven Rostedt
Date: Wed Jan 30 2008 - 16:17:25 EST

Add preempt off timings. A lot of kernel core code is taken from the RT patch
latency trace that was written by Ingo Molnar.

This adds "preemptoff" and "preemptirqsoff" to /debugfs/tracing/available_tracers

Now instead of just tracing irqs off, preemption off can be selected
to be recorded.

When this is selected, it shares the same files as irqs off timings.
One can either trace preemption off, irqs off, or one or the other off.

By echoing "preemptoff" into /debugfs/tracing/current_tracer, recording
of preempt off only is performed. "irqsoff" will only record the time
irqs are disabled, but "preemptirqsoff" will take the total time irqs
or preemption are disabled. Runtime switching of these options is now
supported by simpling echoing in the appropriate trace name into
/debugfs/tracing/current_tracer.

Signed-off-by: Steven Rostedt <srostedt@xxxxxxxxxx>
---
arch/x86/kernel/process_32.c | 3
include/linux/irqflags.h | 3
include/linux/mcount.h | 8 +
include/linux/preempt.h | 2
kernel/sched.c | 24 +++++
lib/tracing/Kconfig | 25 +++++
lib/tracing/Makefile | 1
lib/tracing/trace_irqsoff.c | 183 +++++++++++++++++++++++++++++++------------
8 files changed, 196 insertions(+), 53 deletions(-)

Index: linux-mcount.git/lib/tracing/Kconfig
===================================================================
--- linux-mcount.git.orig/lib/tracing/Kconfig 2008-01-30 15:59:46.000000000 -0500
+++ linux-mcount.git/lib/tracing/Kconfig 2008-01-30 15:59:51.000000000 -0500
@@ -46,6 +46,31 @@ config CRITICAL_IRQSOFF_TIMING

echo 0 > /debugfs/tracing/tracing_max_latency

+ (Note that kernel size and overhead increases with this option
+ enabled. This option and the preempt-off timing option can be
+ used together or separately.)
+
+config CRITICAL_PREEMPT_TIMING
+ bool "Preemption-off critical section latency timing"
+ default n
+ depends on GENERIC_TIME
+ depends on PREEMPT
+ select TRACING
+ select TRACER_MAX_TRACE
+ help
+ This option measures the time spent in preemption off critical
+ sections, with microsecond accuracy.
+
+ The default measurement method is a maximum search, which is
+ disabled by default and can be runtime (re-)started
+ via:
+
+ echo 0 > /debugfs/tracing/tracing_max_latency
+
+ (Note that kernel size and overhead increases with this option
+ enabled. This option and the irqs-off timing option can be
+ used together or separately.)
+
config WAKEUP_TRACER
bool "Trace wakeup latencies"
depends on DEBUG_KERNEL
Index: linux-mcount.git/lib/tracing/Makefile
===================================================================
--- linux-mcount.git.orig/lib/tracing/Makefile 2008-01-30 15:59:46.000000000 -0500
+++ linux-mcount.git/lib/tracing/Makefile 2008-01-30 15:59:51.000000000 -0500
@@ -4,6 +4,7 @@ obj-$(CONFIG_TRACING) += tracer.o
obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o
obj-$(CONFIG_FUNCTION_TRACER) += trace_function.o
obj-$(CONFIG_CRITICAL_IRQSOFF_TIMING) += trace_irqsoff.o
+obj-$(CONFIG_CRITICAL_PREEMPT_TIMING) += trace_irqsoff.o
obj-$(CONFIG_WAKEUP_TRACER) += trace_wakeup.o

libmcount-y := mcount.o
Index: linux-mcount.git/lib/tracing/trace_irqsoff.c
===================================================================
--- linux-mcount.git.orig/lib/tracing/trace_irqsoff.c 2008-01-30 15:59:46.000000000 -0500
+++ linux-mcount.git/lib/tracing/trace_irqsoff.c 2008-01-30 16:00:22.000000000 -0500
@@ -21,6 +21,34 @@ static struct tracing_trace *tracer_trac
static __cacheline_aligned_in_smp DEFINE_MUTEX(max_mutex);
static int trace_enabled __read_mostly;

+static DEFINE_PER_CPU(int, tracing_cpu);
+
+enum {
+ TRACER_IRQS_OFF = (1 << 1),
+ TRACER_PREEMPT_OFF = (1 << 2),
+};
+
+static int trace_type __read_mostly;
+
+#ifdef CONFIG_CRITICAL_PREEMPT_TIMING
+# define preempt_trace() \
+ ((trace_type & TRACER_PREEMPT_OFF) && preempt_count())
+#else
+# define preempt_trace() (0)
+#endif
+
+#ifdef CONFIG_CRITICAL_IRQSOFF_TIMING
+# define irq_trace() \
+ ((trace_type & TRACER_IRQS_OFF) && \
+ ({ \
+ unsigned long __flags; \
+ local_save_flags(__flags); \
+ irqs_disabled_flags(__flags); \
+ }))
+#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
@@ -42,14 +70,11 @@ static void notrace irqsoff_trace_call(u
long disabled;
int cpu;

- if (likely(!trace_enabled))
+ if (likely(!__get_cpu_var(tracing_cpu)))
return;

local_save_flags(flags);

- if (!irqs_disabled_flags(flags))
- return;
-
cpu = raw_smp_processor_id();
data = tr->data[cpu];
disabled = atomic_inc_return(&data->disabled);
@@ -172,23 +197,29 @@ start_critical_timing(unsigned long ip,
if (likely(!trace_enabled))
return;

+ if (__get_cpu_var(tracing_cpu))
+ return;
+
cpu = raw_smp_processor_id();
data = tr->data[cpu];

if (unlikely(!data) || unlikely(!data->trace) ||
- data->critical_start || atomic_read(&data->disabled))
+ atomic_read(&data->disabled))
return;

atomic_inc(&data->disabled);

data->critical_sequence = max_sequence;
data->preempt_timestamp = now();
- data->critical_start = parent_ip;
+ data->critical_start = parent_ip ? : ip;
tracing_reset(data);

local_save_flags(flags);
+
tracing_function_trace(tr, data, ip, parent_ip, flags);

+ __get_cpu_var(tracing_cpu) = 1;
+
atomic_dec(&data->disabled);
}

@@ -200,7 +231,13 @@ stop_critical_timing(unsigned long ip, u
struct tracing_trace_cpu *data;
unsigned long flags;

- if (likely(!trace_enabled))
+ /* Always clear the tracing cpu on stopping the trace */
+ if (unlikely(__get_cpu_var(tracing_cpu)))
+ __get_cpu_var(tracing_cpu) = 0;
+ else
+ return;
+
+ if (!trace_enabled)
return;

cpu = raw_smp_processor_id();
@@ -213,49 +250,35 @@ stop_critical_timing(unsigned long ip, u
atomic_inc(&data->disabled);
local_save_flags(flags);
tracing_function_trace(tr, data, ip, parent_ip, flags);
- check_critical_timing(tr, data, parent_ip, cpu);
+ 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 notrace start_critical_timings(void)
{
- unsigned long flags;
-
- local_save_flags(flags);
-
- if (irqs_disabled_flags(flags))
+ if (preempt_trace() || irq_trace())
start_critical_timing(CALLER_ADDR0, 0);
}

void notrace stop_critical_timings(void)
{
- unsigned long flags;
-
- local_save_flags(flags);
-
- if (irqs_disabled_flags(flags))
+ if (preempt_trace() || irq_trace())
stop_critical_timing(CALLER_ADDR0, 0);
}

+#ifdef CONFIG_CRITICAL_IRQSOFF_TIMING
#ifdef CONFIG_LOCKDEP
void notrace time_hardirqs_on(unsigned long a0, unsigned long a1)
{
- unsigned long flags;
-
- local_save_flags(flags);
-
- if (irqs_disabled_flags(flags))
+ if (!preempt_trace() && irq_trace())
stop_critical_timing(a0, a1);
}

void notrace time_hardirqs_off(unsigned long a0, unsigned long a1)
{
- unsigned long flags;
-
- local_save_flags(flags);
-
- if (irqs_disabled_flags(flags))
+ if (!preempt_trace() && irq_trace())
start_critical_timing(a0, a1);
}

@@ -290,49 +313,46 @@ inline void print_irqtrace_events(struct
*/
void notrace trace_hardirqs_on(void)
{
- unsigned long flags;
-
- local_save_flags(flags);
-
- if (irqs_disabled_flags(flags))
+ if (!preempt_trace() && irq_trace())
stop_critical_timing(CALLER_ADDR0, 0);
}
EXPORT_SYMBOL(trace_hardirqs_on);

void notrace trace_hardirqs_off(void)
{
- unsigned long flags;
-
- local_save_flags(flags);
-
- if (irqs_disabled_flags(flags))
+ if (!preempt_trace() && irq_trace())
start_critical_timing(CALLER_ADDR0, 0);
}
EXPORT_SYMBOL(trace_hardirqs_off);

void notrace trace_hardirqs_on_caller(unsigned long caller_addr)
{
- unsigned long flags;
-
- local_save_flags(flags);
-
- if (irqs_disabled_flags(flags))
+ if (!preempt_trace() && irq_trace())
stop_critical_timing(CALLER_ADDR0, caller_addr);
}
EXPORT_SYMBOL(trace_hardirqs_on_caller);

void notrace trace_hardirqs_off_caller(unsigned long caller_addr)
{
- unsigned long flags;
-
- local_save_flags(flags);
-
- if (irqs_disabled_flags(flags))
+ if (!preempt_trace() && irq_trace())
start_critical_timing(CALLER_ADDR0, caller_addr);
}
EXPORT_SYMBOL(trace_hardirqs_off_caller);

#endif /* CONFIG_LOCKDEP */
+#endif /* CONFIG_CRITICAL_IRQSOFF_TIMING */
+
+#ifdef CONFIG_CRITICAL_PREEMPT_TIMING
+void notrace trace_preempt_on(unsigned long a0, unsigned long a1)
+{
+ stop_critical_timing(a0, a1);
+}
+
+void notrace trace_preempt_off(unsigned long a0, unsigned long a1)
+{
+ start_critical_timing(a0, a1);
+}
+#endif /* CONFIG_CRITICAL_PREEMPT_TIMING */

static void start_irqsoff_trace(struct tracing_trace *tr)
{
@@ -346,7 +366,7 @@ static void stop_irqsoff_trace(struct tr
trace_enabled = 0;
}

-static void irqsoff_trace_init(struct tracing_trace *tr)
+static void __irqsoff_trace_init(struct tracing_trace *tr)
{
tracer_trace = tr;
/* make sure that the tracer is visibel */
@@ -393,6 +413,13 @@ static void irqsoff_trace_stop(struct tr
mutex_unlock(&max_mutex);
}

+#ifdef CONFIG_CRITICAL_IRQSOFF_TIMING
+static void irqsoff_trace_init(struct tracing_trace *tr)
+{
+ trace_type = TRACER_IRQS_OFF;
+
+ __irqsoff_trace_init(tr);
+}
static struct trace_types_struct irqsoff_trace __read_mostly =
{
.name = "irqsoff",
@@ -405,10 +432,66 @@ static struct trace_types_struct irqsoff
.ctrl_update = irqsoff_trace_ctrl_update,
.print_max = 1,
};
+# define register_irqsoff(trace) register_trace(&trace)
+#else
+# define register_irqsoff(trace) do { } while (0)
+#endif
+
+#ifdef CONFIG_CRITICAL_PREEMPT_TIMING
+static void preemptoff_trace_init(struct tracing_trace *tr)
+{
+ trace_type = TRACER_PREEMPT_OFF;
+
+ __irqsoff_trace_init(tr);
+}
+static struct trace_types_struct preemptoff_trace __read_mostly =
+{
+ .name = "preemptoff",
+ .init = preemptoff_trace_init,
+ .reset = irqsoff_trace_reset,
+ .open = irqsoff_trace_open,
+ .close = irqsoff_trace_close,
+ .start = irqsoff_trace_start,
+ .stop = irqsoff_trace_stop,
+ .ctrl_update = irqsoff_trace_ctrl_update,
+ .print_max = 1,
+};
+# define register_preemptoff(trace) register_trace(&trace)
+#else
+# define register_preemptoff(trace) do { } while (0)
+#endif
+
+
+#if defined(CONFIG_CRITICAL_IRQSOFF_TIMING) && \
+ defined(CONFIG_CRITICAL_PREEMPT_TIMING)
+static void preemptirqsoff_trace_init(struct tracing_trace *tr)
+{
+ trace_type = TRACER_IRQS_OFF | TRACER_PREEMPT_OFF;
+
+ __irqsoff_trace_init(tr);
+}
+static struct trace_types_struct preemptirqsoff_trace __read_mostly =
+{
+ .name = "preemptirqsoff",
+ .init = preemptirqsoff_trace_init,
+ .reset = irqsoff_trace_reset,
+ .open = irqsoff_trace_open,
+ .close = irqsoff_trace_close,
+ .start = irqsoff_trace_start,
+ .stop = irqsoff_trace_stop,
+ .ctrl_update = irqsoff_trace_ctrl_update,
+ .print_max = 1,
+};
+# define register_preemptirqsoff(trace) register_trace(&trace)
+#else
+# define register_preemptirqsoff(trace) do { } while (0)
+#endif

__init static int init_irqsoff_trace(void)
{
- register_trace(&irqsoff_trace);
+ register_irqsoff(irqsoff_trace);
+ register_preemptoff(preemptoff_trace);
+ register_preemptirqsoff(preemptirqsoff_trace);

return 0;
}
Index: linux-mcount.git/include/linux/preempt.h
===================================================================
--- linux-mcount.git.orig/include/linux/preempt.h 2008-01-30 15:58:35.000000000 -0500
+++ linux-mcount.git/include/linux/preempt.h 2008-01-30 15:59:51.000000000 -0500
@@ -10,7 +10,7 @@
#include <linux/linkage.h>
#include <linux/list.h>

-#ifdef CONFIG_DEBUG_PREEMPT
+#if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_CRITICAL_PREEMPT_TIMING)
extern void fastcall add_preempt_count(int val);
extern void fastcall sub_preempt_count(int val);
#else
Index: linux-mcount.git/kernel/sched.c
===================================================================
--- linux-mcount.git.orig/kernel/sched.c 2008-01-30 15:59:33.000000000 -0500
+++ linux-mcount.git/kernel/sched.c 2008-01-30 15:59:51.000000000 -0500
@@ -66,6 +66,7 @@
#include <linux/unistd.h>
#include <linux/pagemap.h>
#include <linux/hrtimer.h>
+#include <linux/mcount.h>

#include <asm/tlb.h>
#include <asm/irq_regs.h>
@@ -3780,26 +3781,44 @@ void scheduler_tick(void)
#endif
}

-#if defined(CONFIG_PREEMPT) && defined(CONFIG_DEBUG_PREEMPT)
+#if defined(CONFIG_PREEMPT) && (defined(CONFIG_DEBUG_PREEMPT) || \
+ defined(CONFIG_CRITICAL_PREEMPT_TIMING))
+
+static inline unsigned long get_parent_ip(unsigned long addr)
+{
+ if (in_lock_functions(addr)) {
+ addr = CALLER_ADDR2;
+ if (in_lock_functions(addr))
+ addr = CALLER_ADDR3;
+ }
+ return addr;
+}

void fastcall add_preempt_count(int val)
{
+#ifdef CONFIG_DEBUG_PREEMPT
/*
* Underflow?
*/
if (DEBUG_LOCKS_WARN_ON((preempt_count() < 0)))
return;
+#endif
preempt_count() += val;
+#ifdef CONFIG_DEBUG_PREEMPT
/*
* Spinlock count overflowing soon?
*/
DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >=
PREEMPT_MASK - 10);
+#endif
+ if (preempt_count() == val)
+ trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
}
EXPORT_SYMBOL(add_preempt_count);

void fastcall sub_preempt_count(int val)
{
+#ifdef CONFIG_DEBUG_PREEMPT
/*
* Underflow?
*/
@@ -3811,7 +3830,10 @@ void fastcall sub_preempt_count(int val)
if (DEBUG_LOCKS_WARN_ON((val < PREEMPT_MASK) &&
!(preempt_count() & PREEMPT_MASK)))
return;
+#endif

+ if (preempt_count() == val)
+ trace_preempt_on(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
preempt_count() -= val;
}
EXPORT_SYMBOL(sub_preempt_count);
Index: linux-mcount.git/arch/x86/kernel/process_32.c
===================================================================
--- linux-mcount.git.orig/arch/x86/kernel/process_32.c 2008-01-30 15:57:14.000000000 -0500
+++ linux-mcount.git/arch/x86/kernel/process_32.c 2008-01-30 15:59:51.000000000 -0500
@@ -195,7 +195,10 @@ void cpu_idle(void)
play_dead();

__get_cpu_var(irq_stat).idle_timestamp = jiffies;
+ /* Don't trace irqs off for idle */
+ stop_critical_timings();
idle();
+ start_critical_timings();
}
tick_nohz_restart_sched_tick();
preempt_enable_no_resched();
Index: linux-mcount.git/include/linux/mcount.h
===================================================================
--- linux-mcount.git.orig/include/linux/mcount.h 2008-01-30 15:59:46.000000000 -0500
+++ linux-mcount.git/include/linux/mcount.h 2008-01-30 15:59:51.000000000 -0500
@@ -58,4 +58,12 @@ extern void mcount(void);
# define time_hardirqs_off(a0, a1) do { } while (0)
#endif

+#ifdef CONFIG_CRITICAL_PREEMPT_TIMING
+ extern void notrace trace_preempt_on(unsigned long a0, unsigned long a1);
+ extern void notrace trace_preempt_off(unsigned long a0, unsigned long a1);
+#else
+# define trace_preempt_on(a0, a1) do { } while (0)
+# define trace_preempt_off(a0, a1) do { } while (0)
+#endif
+
#endif /* _LINUX_MCOUNT_H */
Index: linux-mcount.git/include/linux/irqflags.h
===================================================================
--- linux-mcount.git.orig/include/linux/irqflags.h 2008-01-30 15:59:46.000000000 -0500
+++ linux-mcount.git/include/linux/irqflags.h 2008-01-30 15:59:51.000000000 -0500
@@ -54,7 +54,8 @@
# define INIT_TRACE_IRQFLAGS
#endif

-#ifdef CONFIG_CRITICAL_IRQSOFF_TIMING
+#if defined(CONFIG_CRITICAL_IRQSOFF_TIMING) || \
+ defined(CONFIG_CRITICAL_PREEMPT_TIMING)
extern void stop_critical_timings(void);
extern void start_critical_timings(void);
#else

--
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