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Subject[PATCH 2/2 v2][RFC] ftrace: unlikely annotation tracer

This patch adds a way to record the instances of the likely and unlikely
condition annotations.

When "unlikely" is set in /debugfs/tracing/iter_ctrl the unlikely conditions
will be added to any of the ftrace tracers.

For example:

irqbalance-2662 [002] 41127.102858: [correct] debug_mutex_free_waiter 51
<idle>-0 [001] 41127.102858: [correct] add_preempt_count 4307
irqbalance-2662 [002] 41127.102859: [INCORRECT] debug_smp_processor_id 15
<idle>-0 [001] 41127.102860: [correct] add_preempt_count 4316
irqbalance-2662 [002] 41127.102861: [correct] slab_alloc 1608

Which shows the normal tracer heading, as well as whether the condition was
correct "[correct]" or was mistaken "[INCORRECT]", followed by the
function and line number.


Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
kernel/Makefile | 5 +
kernel/trace/Kconfig | 22 +++++++
kernel/trace/Makefile | 5 +
kernel/trace/ring_buffer.c | 11 +++
kernel/trace/trace.c | 37 +++++++++++
kernel/trace/trace.h | 43 +++++++++++++
kernel/trace/trace_unlikely.c | 130 ++++++++++++++++++++++++++++++++++++++++++
7 files changed, 253 insertions(+)
Index: linux-tip.git/kernel/trace/Kconfig
===================================================================
--- linux-tip.git.orig/kernel/trace/Kconfig 2008-10-29 12:32:30.000000000 -0400
+++ linux-tip.git/kernel/trace/Kconfig 2008-10-29 12:32:35.000000000 -0400
@@ -154,6 +154,28 @@ config TRACE_UNLIKELY_PROFILE

Say N if unsure.

+config TRACING_UNLIKELY
+ bool
+ help
+ Selected by tracers that will trace the likely and unlikely
+ conditions. This prevents the tracers themselves from being
+ profiled. Profiling the tracing infrastructure can only happen
+ when the likelys and unlikelys are not being traced.
+
+config UNLIKELY_TRACER
+ bool "Trace likely/unlikely instances"
+ depends on TRACE_UNLIKELY_PROFILE
+ select TRACING_UNLIKELY
+ help
+ This is traces the events of likely and unlikely condition
+ calls in the kernel. The difference between this and the
+ "Trace likely/unlikely profiler" is that this is not a
+ histogram of the callers, but actually places the calling
+ events into a running buffer to see when and where the
+ events happened, as well as their results.
+
+ Say N if unsure.
+
config STACK_TRACER
bool "Trace max stack"
depends on HAVE_FUNCTION_TRACER
Index: linux-tip.git/kernel/Makefile
===================================================================
--- linux-tip.git.orig/kernel/Makefile 2008-10-29 12:32:30.000000000 -0400
+++ linux-tip.git/kernel/Makefile 2008-10-29 12:32:35.000000000 -0400
@@ -24,6 +24,11 @@ CFLAGS_REMOVE_sched_clock.o = -pg
CFLAGS_REMOVE_sched.o = -mno-spe -pg
endif

+ifdef CONFIG_TRACING_UNLIKELY
+# Do not profile tracepoint if we are tracing the unlikely conditions
+CFLAGS_tracepoint.o += '-Dunlikely(x)=unlikely_notrace(x)'
+endif
+
obj-$(CONFIG_FREEZER) += freezer.o
obj-$(CONFIG_PROFILING) += profile.o
obj-$(CONFIG_SYSCTL_SYSCALL_CHECK) += sysctl_check.o
Index: linux-tip.git/kernel/trace/Makefile
===================================================================
--- linux-tip.git.orig/kernel/trace/Makefile 2008-10-29 12:32:30.000000000 -0400
+++ linux-tip.git/kernel/trace/Makefile 2008-10-29 12:32:35.000000000 -0400
@@ -10,6 +10,11 @@ CFLAGS_trace_selftest_dynamic.o = -pg
obj-y += trace_selftest_dynamic.o
endif

+ifdef CONFIG_TRACING_UNLIKELY
+KBUILD_CFLAGS += '-Dlikely(x)=likely_notrace(x)'
+KBUILD_CFLAGS += '-Dunlikely(x)=unlikely_notrace(x)'
+endif
+
obj-$(CONFIG_FUNCTION_TRACER) += libftrace.o
obj-$(CONFIG_RING_BUFFER) += ring_buffer.o

Index: linux-tip.git/kernel/trace/trace_unlikely.c
===================================================================
--- linux-tip.git.orig/kernel/trace/trace_unlikely.c 2008-10-29 12:32:30.000000000 -0400
+++ linux-tip.git/kernel/trace/trace_unlikely.c 2008-10-29 12:32:35.000000000 -0400
@@ -15,8 +15,138 @@
#include <asm/local.h>
#include "trace.h"

+#ifdef CONFIG_UNLIKELY_TRACER
+
+static int unlikely_tracing_enabled __read_mostly;
+static DEFINE_MUTEX(unlikely_tracing_mutex);
+static DEFINE_PER_CPU(atomic_t, unlikely_trace_disabled);
+static struct trace_array *unlikely_tracer;
+
+void trace_unlikely_stop(void)
+{
+ /* preemption should be disabled */
+ int cpu = smp_processor_id();
+
+ atomic_inc(&per_cpu(unlikely_trace_disabled, cpu));
+}
+
+void trace_unlikely_start(void)
+{
+ /* preemption should be disabled */
+ int cpu = smp_processor_id();
+
+ atomic_dec(&per_cpu(unlikely_trace_disabled, cpu));
+}
+
+static void
+probe_likely_condition(struct ftrace_likely_data *f, int val, int expect)
+{
+ struct trace_array *tr = unlikely_tracer;
+ struct ring_buffer_event *event;
+ struct trace_unlikely *entry;
+ unsigned long flags, irq_flags;
+ int cpu, resched, pc;
+
+ if (unlikely(!tr))
+ return;
+
+ pc = preempt_count();
+ /* Can be called within schedule */
+ resched = need_resched();
+ preempt_disable_notrace();
+ cpu = raw_smp_processor_id();
+ if (atomic_inc_return(&per_cpu(unlikely_trace_disabled, cpu)) != 1)
+ goto out;
+
+ event = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry),
+ &irq_flags);
+ if (!event)
+ goto out;
+
+ local_save_flags(flags);
+ entry = ring_buffer_event_data(event);
+ tracing_generic_entry_update(&entry->ent, flags, pc);
+ entry->ent.type = TRACE_UNLIKELY;
+
+ /*
+ * I would love to save just the ftrace_likely_data pointer, but
+ * this code can also be used by modules. Ugly things can happen
+ * if the module is unloaded, and then we go and read the
+ * pointer. This is slower, but much safer.
+ */
+
+ strncpy(entry->func, f->func, TRACE_FUNC_SIZE);
+ strncpy(entry->file, f->file, TRACE_FILE_SIZE);
+ entry->func[TRACE_FUNC_SIZE] = 0;
+ entry->file[TRACE_FILE_SIZE] = 0;
+ entry->line = f->line;
+ entry->correct = val == expect;
+
+ ring_buffer_unlock_commit(tr->buffer, event, irq_flags);
+
+ out:
+ atomic_dec(&per_cpu(unlikely_trace_disabled, cpu));
+ if (resched)
+ preempt_enable_no_resched_notrace();
+ else
+ preempt_enable_notrace();
+}
+
+static inline
+void trace_likely_condition(struct ftrace_likely_data *f, int val, int expect)
+{
+ if (!unlikely_tracing_enabled)
+ return;
+
+ probe_likely_condition(f, val, expect);
+}
+
+int enable_unlikely_tracing(struct trace_array *tr)
+{
+ int ret = 0;
+
+ mutex_lock(&unlikely_tracing_mutex);
+ unlikely_tracer = tr;
+ /*
+ * Must be seen before enabling. The reader is a condition
+ * where we do not need a matching rmb()
+ */
+ smp_wmb();
+ unlikely_tracing_enabled++;
+ mutex_unlock(&unlikely_tracing_mutex);
+
+ return ret;
+}
+
+void disable_unlikely_tracing(void)
+{
+ mutex_lock(&unlikely_tracing_mutex);
+
+ if (!unlikely_tracing_enabled)
+ goto out_unlock;
+
+ unlikely_tracing_enabled--;
+
+ out_unlock:
+ mutex_unlock(&unlikely_tracing_mutex);
+}
+#else
+static inline
+void trace_likely_condition(struct ftrace_likely_data *f, int val, int expect)
+{
+}
+#endif /* CONFIG_UNLIKELY_TRACER */
+
void ftrace_likely_update(struct ftrace_likely_data *f, int val, int expect)
{
+ /*
+ * I would love to have a trace point here instead, but the
+ * trace point code is so inundated with unlikely and likely
+ * conditions that the recursive nightmare that exists is too
+ * much to try to get working. At least for now.
+ */
+ trace_likely_condition(f, val, expect);
+
/* FIXME: Make this atomic! */
if (val == expect)
f->correct++;
Index: linux-tip.git/kernel/trace/trace.c
===================================================================
--- linux-tip.git.orig/kernel/trace/trace.c 2008-10-29 12:32:30.000000000 -0400
+++ linux-tip.git/kernel/trace/trace.c 2008-10-29 12:32:35.000000000 -0400
@@ -235,6 +235,9 @@ static const char *trace_options[] = {
"stacktrace",
"sched-tree",
"ftrace_printk",
+#ifdef CONFIG_UNLIKELY_TRACER
+ "unlikely",
+#endif
NULL
};

@@ -1457,6 +1460,17 @@ print_lat_fmt(struct trace_iterator *ite
trace_seq_print_cont(s, iter);
break;
}
+ case TRACE_UNLIKELY: {
+ struct trace_unlikely *field;
+
+ trace_assign_type(field, entry);
+
+ trace_seq_printf(s, "[%s] %-30.30s %d\n",
+ field->correct ? "correct" : "INCORRECT",
+ field->func,
+ field->line);
+ break;
+ }
default:
trace_seq_printf(s, "Unknown type %d\n", entry->type);
}
@@ -1593,6 +1607,17 @@ static enum print_line_t print_trace_fmt
trace_seq_print_cont(s, iter);
break;
}
+ case TRACE_UNLIKELY: {
+ struct trace_unlikely *field;
+
+ trace_assign_type(field, entry);
+
+ trace_seq_printf(s, "[%s] %-30.30s %d\n",
+ field->correct ? "correct" : "INCORRECT",
+ field->func,
+ field->line);
+ break;
+ }
}
return TRACE_TYPE_HANDLED;
}
@@ -1675,6 +1700,10 @@ static enum print_line_t print_raw_fmt(s
trace_seq_print_cont(s, iter);
break;
}
+ case TRACE_UNLIKELY: {
+ /* IGNORE */
+ break;
+ };
}
return TRACE_TYPE_HANDLED;
}
@@ -2362,8 +2391,14 @@ tracing_ctrl_write(struct file *filp, co

tr->ctrl = val;

+ if (!val)
+ trace_unlikely_disable();
+
if (current_trace && current_trace->ctrl_update)
current_trace->ctrl_update(tr);
+
+ if (val)
+ trace_unlikely_enable(tr);
}
mutex_unlock(&trace_types_lock);

@@ -2425,6 +2460,7 @@ tracing_set_trace_write(struct file *fil
if (t == current_trace)
goto out;

+ trace_unlikely_disable();
if (current_trace && current_trace->reset)
current_trace->reset(tr);

@@ -2432,6 +2468,7 @@ tracing_set_trace_write(struct file *fil
if (t->init)
t->init(tr);

+ trace_unlikely_enable(tr);
out:
mutex_unlock(&trace_types_lock);

Index: linux-tip.git/kernel/trace/trace.h
===================================================================
--- linux-tip.git.orig/kernel/trace/trace.h 2008-10-29 12:32:30.000000000 -0400
+++ linux-tip.git/kernel/trace/trace.h 2008-10-29 12:32:35.000000000 -0400
@@ -21,6 +21,7 @@ enum trace_type {
TRACE_SPECIAL,
TRACE_MMIO_RW,
TRACE_MMIO_MAP,
+ TRACE_UNLIKELY,
TRACE_BOOT,

__TRACE_LAST_TYPE
@@ -117,6 +118,16 @@ struct trace_boot {
struct boot_trace initcall;
};

+#define TRACE_FUNC_SIZE 30
+#define TRACE_FILE_SIZE 20
+struct trace_unlikely {
+ struct trace_entry ent;
+ unsigned line;
+ char func[TRACE_FUNC_SIZE+1];
+ char file[TRACE_FILE_SIZE+1];
+ char correct;
+};
+
/*
* trace_flag_type is an enumeration that holds different
* states when a trace occurs. These are:
@@ -217,6 +228,7 @@ extern void __ftrace_bad_type(void);
IF_ASSIGN(var, ent, struct trace_mmiotrace_map, \
TRACE_MMIO_MAP); \
IF_ASSIGN(var, ent, struct trace_boot, TRACE_BOOT); \
+ IF_ASSIGN(var, ent, struct trace_unlikely, TRACE_UNLIKELY); \
__ftrace_bad_type(); \
} while (0)

@@ -413,8 +425,39 @@ enum trace_iterator_flags {
TRACE_ITER_STACKTRACE = 0x100,
TRACE_ITER_SCHED_TREE = 0x200,
TRACE_ITER_PRINTK = 0x400,
+#ifdef CONFIG_UNLIKELY_TRACER
+ TRACE_ITER_UNLIKELY = 0x800,
+#endif
};

extern struct tracer nop_trace;

+#ifdef CONFIG_UNLIKELY_TRACER
+extern int enable_unlikely_tracing(struct trace_array *tr);
+extern void disable_unlikely_tracing(void);
+static inline int trace_unlikely_enable(struct trace_array *tr)
+{
+ if (trace_flags & TRACE_ITER_UNLIKELY)
+ return enable_unlikely_tracing(tr);
+ return 0;
+}
+static inline void trace_unlikely_disable(void)
+{
+ /* due to races, always disable */
+ disable_unlikely_tracing();
+}
+extern void trace_unlikely_stop(void);
+extern void trace_unlikely_start(void);
+#else
+static inline int trace_unlikely_enable(struct trace_array *tr)
+{
+ return 0;
+}
+static inline void trace_unlikely_disable(void)
+{
+}
+static inline void trace_unlikely_stop(void) { }
+static inline void trace_unlikely_start(void) { }
+#endif /* CONFIG_UNLIKELY_TRACER */
+
#endif /* _LINUX_KERNEL_TRACE_H */
Index: linux-tip.git/kernel/trace/ring_buffer.c
===================================================================
--- linux-tip.git.orig/kernel/trace/ring_buffer.c 2008-10-29 12:32:30.000000000 -0400
+++ linux-tip.git/kernel/trace/ring_buffer.c 2008-10-29 12:32:35.000000000 -0400
@@ -16,6 +16,8 @@
#include <linux/list.h>
#include <linux/fs.h>

+#include "trace.h"
+
/* Up this if you want to test the TIME_EXTENTS and normalization */
#define DEBUG_SHIFT 0

@@ -1139,7 +1141,14 @@ ring_buffer_lock_reserve(struct ring_buf
if (length > BUF_PAGE_SIZE)
goto out;

+ /*
+ * Ugly, but the unlikely tracing will enter back into
+ * the ring buffer code. Namely through the timestamp, causing
+ * a triggering of the "again" loop, that will be infinite.
+ */
+ trace_unlikely_stop();
event = rb_reserve_next_event(cpu_buffer, RINGBUF_TYPE_DATA, length);
+ trace_unlikely_start();
if (!event)
goto out;

@@ -1251,8 +1260,10 @@ int ring_buffer_write(struct ring_buffer
goto out;

event_length = rb_calculate_event_length(length);
+ trace_unlikely_stop();
event = rb_reserve_next_event(cpu_buffer,
RINGBUF_TYPE_DATA, event_length);
+ trace_unlikely_start();
if (!event)
goto out;




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