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Subject[PATCH 14/20 -v5] Add tracing of context switches
This patch adds context switch tracing, of the format of:

_------=> CPU#
/ _-----=> irqs-off
| / _----=> need-resched
|| / _---=> hardirq/softirq
||| / _--=> preempt-depth
|||| /
||||| delay
cmd pid ||||| time | caller
\ / ||||| \ | /
swapper-0 1d..3 137us+: 0:140:R --> 2912:120
sshd-2912 1d..3 216us+: 2912:120:S --> 0:140
swapper-0 1d..3 261us+: 0:140:R --> 2912:120
bash-2920 0d..3 267us+: 2920:120:S --> 0:140
sshd-2912 1d..3 330us!: 2912:120:S --> 0:140
swapper-0 1d..3 2389us+: 0:140:R --> 2847:120
yum-upda-2847 1d..3 2411us!: 2847:120:S --> 0:140
swapper-0 0d..3 11089us+: 0:140:R --> 3139:120
gdm-bina-3139 0d..3 11113us!: 3139:120:S --> 0:140
swapper-0 1d..3 102328us+: 0:140:R --> 2847:120
yum-upda-2847 1d..3 102348us!: 2847:120:S --> 0:140

"sched_switch" is added to /debugfs/tracing/available_tracers

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---
lib/tracing/Kconfig | 9 ++
lib/tracing/Makefile | 1
lib/tracing/trace_sched_switch.c | 134 +++++++++++++++++++++++++++++++++++++++
lib/tracing/tracer.c | 32 +++++++++
lib/tracing/tracer.h | 19 +++++
5 files changed, 194 insertions(+), 1 deletion(-)
Index: linux-mcount.git/lib/tracing/Kconfig
===================================================================
--- linux-mcount.git.orig/lib/tracing/Kconfig 2008-01-23 10:27:19.000000000 -0500
+++ linux-mcount.git/lib/tracing/Kconfig 2008-01-23 10:27:31.000000000 -0500
@@ -23,3 +23,12 @@ config FUNCTION_TRACER
insert a call to an architecture specific __mcount routine,
that the debugging mechanism using this facility will hook by
providing a set of inline routines.
+
+config CONTEXT_SWITCH_TRACER
+ bool "Trace process context switches"
+ depends on DEBUG_KERNEL
+ select TRACING
+ help
+ This tracer hooks into the context switch and records
+ all switching of tasks.
+
Index: linux-mcount.git/lib/tracing/Makefile
===================================================================
--- linux-mcount.git.orig/lib/tracing/Makefile 2008-01-23 10:27:19.000000000 -0500
+++ linux-mcount.git/lib/tracing/Makefile 2008-01-23 10:27:31.000000000 -0500
@@ -1,6 +1,7 @@
obj-$(CONFIG_MCOUNT) += libmcount.o

obj-$(CONFIG_TRACING) += tracer.o
+obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o
obj-$(CONFIG_FUNCTION_TRACER) += trace_function.o

libmcount-y := mcount.o
Index: linux-mcount.git/lib/tracing/trace_sched_switch.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-mcount.git/lib/tracing/trace_sched_switch.c 2008-01-23 10:27:31.000000000 -0500
@@ -0,0 +1,134 @@
+/*
+ * trace context switch
+ *
+ * Copyright (C) 2007 Steven Rostedt <srostedt@redhat.com>
+ *
+ */
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/debugfs.h>
+#include <linux/kallsyms.h>
+#include <linux/uaccess.h>
+#include <linux/marker.h>
+#include <linux/mcount.h>
+
+#include "tracer.h"
+
+static struct tracing_trace *tracer_trace;
+static int trace_enabled __read_mostly;
+
+static notrace void sched_switch_callback(const struct marker *mdata,
+ void *private_data,
+ const char *format, ...)
+{
+ struct tracing_trace **p = mdata->private;
+ struct tracing_trace *tr = *p;
+ struct tracing_trace_cpu *data;
+ struct task_struct *prev;
+ struct task_struct *next;
+ unsigned long flags;
+ va_list ap;
+ int cpu;
+
+ if (likely(!trace_enabled))
+ return;
+
+ va_start(ap, format);
+ prev = va_arg(ap, typeof(prev));
+ next = va_arg(ap, typeof(next));
+ va_end(ap);
+
+ raw_local_irq_save(flags);
+ cpu = raw_smp_processor_id();
+ data = tr->data[cpu];
+ atomic_inc(&data->disabled);
+
+ if (likely(atomic_read(&data->disabled) == 1))
+ tracing_sched_switch_trace(tr, data, prev, next, flags);
+
+ atomic_dec(&data->disabled);
+ raw_local_irq_restore(flags);
+}
+
+static notrace void sched_switch_reset(struct tracing_trace *tr)
+{
+ int cpu;
+
+ tr->time_start = now();
+
+ for_each_online_cpu(cpu)
+ tracing_reset(tr->data[cpu]);
+}
+
+static notrace void start_sched_trace(struct tracing_trace *tr)
+{
+ sched_switch_reset(tr);
+ trace_enabled = 1;
+}
+
+static notrace void stop_sched_trace(struct tracing_trace *tr)
+{
+ trace_enabled = 0;
+}
+
+static notrace void sched_switch_trace_init(struct tracing_trace *tr)
+{
+ tracer_trace = tr;
+
+ if (tr->ctrl)
+ start_sched_trace(tr);
+}
+
+static notrace void sched_switch_trace_reset(struct tracing_trace *tr)
+{
+ if (tr->ctrl)
+ stop_sched_trace(tr);
+}
+
+static void sched_switch_trace_ctrl_update(struct tracing_trace *tr)
+{
+ /* When starting a new trace, reset the buffers */
+ if (tr->ctrl)
+ start_sched_trace(tr);
+ else
+ stop_sched_trace(tr);
+}
+
+static struct trace_types_struct sched_switch_trace __read_mostly =
+{
+ .name = "sched_switch",
+ .init = sched_switch_trace_init,
+ .reset = sched_switch_trace_reset,
+ .ctrl_update = sched_switch_trace_ctrl_update,
+};
+
+
+__init static int init_sched_switch_trace(void)
+{
+ int ret;
+
+ ret = register_trace(&sched_switch_trace);
+ if (ret)
+ return ret;
+
+ ret = marker_probe_register("kernel_sched_schedule",
+ "prev %p next %p",
+ sched_switch_callback,
+ &tracer_trace);
+ if (ret) {
+ pr_info("sched trace: Couldn't add marker"
+ " probe to switch_to\n");
+ goto out;
+ }
+
+ ret = marker_arm("kernel_sched_schedule");
+ if (ret) {
+ pr_info("sched trace: Couldn't arm probe switch_to\n");
+ goto out;
+ }
+
+ out:
+ return ret;
+}
+
+device_initcall(init_sched_switch_trace);
Index: linux-mcount.git/lib/tracing/tracer.c
===================================================================
--- linux-mcount.git.orig/lib/tracing/tracer.c 2008-01-23 10:27:19.000000000 -0500
+++ linux-mcount.git/lib/tracing/tracer.c 2008-01-23 10:27:31.000000000 -0500
@@ -52,6 +52,7 @@ enum trace_type {
__TRACE_FIRST_TYPE = 0,

TRACE_FN,
+ TRACE_CTX,

__TRACE_LAST_TYPE
};
@@ -227,6 +228,24 @@ notrace void tracing_function_trace(stru
entry->fn.parent_ip = parent_ip;
}

+notrace void tracing_sched_switch_trace(struct tracing_trace *tr,
+ struct tracing_trace_cpu *data,
+ struct task_struct *prev,
+ struct task_struct *next,
+ unsigned long flags)
+{
+ struct tracing_entry *entry;
+
+ entry = tracing_get_trace_entry(tr, data);
+ tracing_generic_entry_update(entry, flags);
+ entry->type = TRACE_CTX;
+ entry->ctx.prev_pid = prev->pid;
+ entry->ctx.prev_prio = prev->prio;
+ entry->ctx.prev_state = prev->state;
+ entry->ctx.next_pid = next->pid;
+ entry->ctx.next_prio = next->prio;
+}
+
enum trace_iterator {
TRACE_ITER_SYM_ONLY = 1,
TRACE_ITER_VERBOSE = 2,
@@ -545,6 +564,8 @@ lat_print_timestamp(struct seq_file *m,
seq_puts(m, " : ");
}

+static const char state_to_char[] = TASK_STATE_TO_CHAR_STR;
+
static void notrace
print_lat_fmt(struct seq_file *m, struct tracing_iterator *iter,
unsigned int trace_idx, int cpu)
@@ -555,6 +576,7 @@ print_lat_fmt(struct seq_file *m, struct
unsigned long rel_usecs;
int sym_only = !!(trace_flags & TRACE_ITER_SYM_ONLY);
int verbose = !!(trace_flags & TRACE_ITER_VERBOSE);
+ int S;

if (!next_entry)
next_entry = entry;
@@ -581,6 +603,16 @@ print_lat_fmt(struct seq_file *m, struct
seq_print_ip_sym(m, entry->fn.parent_ip, sym_only);
seq_puts(m, ")\n");
break;
+ case TRACE_CTX:
+ S = entry->ctx.prev_state < sizeof(state_to_char) ?
+ state_to_char[entry->ctx.prev_state] : 'X';
+ seq_printf(m, " %d:%d:%c --> %d:%d\n",
+ entry->ctx.prev_pid,
+ entry->ctx.prev_prio,
+ S,
+ entry->ctx.next_pid,
+ entry->ctx.next_prio);
+ break;
}
}

Index: linux-mcount.git/lib/tracing/tracer.h
===================================================================
--- linux-mcount.git.orig/lib/tracing/tracer.h 2008-01-23 10:27:19.000000000 -0500
+++ linux-mcount.git/lib/tracing/tracer.h 2008-01-23 10:27:31.000000000 -0500
@@ -10,6 +10,14 @@ struct tracing_function {
unsigned long parent_ip;
};

+struct tracing_sched_switch {
+ unsigned int prev_pid;
+ unsigned char prev_prio;
+ unsigned char prev_state;
+ unsigned int next_pid;
+ unsigned char next_prio;
+};
+
struct tracing_entry {
char type;
char cpu; /* who will want to trace more than 256 CPUS? */
@@ -18,7 +26,10 @@ struct tracing_entry {
int pid;
cycle_t t;
char comm[TASK_COMM_LEN];
- struct tracing_function fn;
+ union {
+ struct tracing_function fn;
+ struct tracing_sched_switch ctx;
+ };
};

struct tracing_trace_cpu {
@@ -82,6 +93,12 @@ void tracing_function_trace(struct traci
unsigned long ip,
unsigned long parent_ip,
unsigned long flags);
+void tracing_sched_switch_trace(struct tracing_trace *tr,
+ struct tracing_trace_cpu *data,
+ struct task_struct *prev,
+ struct task_struct *next,
+ unsigned long flags);
+

void tracing_start_function_trace(void);
void tracing_stop_function_trace(void);
--


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