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Subject[PATCH 15/20 -v5] Generic command line storage
Saving the comm of tasks for each trace is very expensive.
This patch includes in the context switch hook, a way to
store the last 100 command lines of tasks. This table is
examined when a trace is to be printed.

Note: The comm may be destroyed if other traces are performed.
Later (TBD) patches may simply store this information in the trace
itself.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
lib/tracing/Kconfig | 1
lib/tracing/trace_function.c | 2
lib/tracing/trace_sched_switch.c | 7 ++
lib/tracing/tracer.c | 104 +++++++++++++++++++++++++++++++++++++--
lib/tracing/tracer.h | 6 +-
5 files changed, 114 insertions(+), 6 deletions(-)
Index: linux-mcount.git/lib/tracing/Kconfig
===================================================================
--- linux-mcount.git.orig/lib/tracing/Kconfig 2008-01-23 10:27:31.000000000 -0500
+++ linux-mcount.git/lib/tracing/Kconfig 2008-01-23 10:27:39.000000000 -0500
@@ -18,6 +18,7 @@ config FUNCTION_TRACER
depends on DEBUG_KERNEL && HAVE_MCOUNT
select MCOUNT
select TRACING
+ select CONTEXT_SWITCH_TRACER
help
Use profiler instrumentation, adding -pg to CFLAGS. This will
insert a call to an architecture specific __mcount routine,
Index: linux-mcount.git/lib/tracing/trace_function.c
===================================================================
--- linux-mcount.git.orig/lib/tracing/trace_function.c 2008-01-23 10:27:19.000000000 -0500
+++ linux-mcount.git/lib/tracing/trace_function.c 2008-01-23 10:27:39.000000000 -0500
@@ -28,11 +28,13 @@ static notrace void function_reset(struc
static notrace void start_function_trace(struct tracing_trace *tr)
{
function_reset(tr);
+ atomic_inc(&trace_record_cmdline);
tracing_start_function_trace();
}

static notrace void stop_function_trace(struct tracing_trace *tr)
{
+ atomic_dec(&trace_record_cmdline);
tracing_stop_function_trace();
}

Index: linux-mcount.git/lib/tracing/trace_sched_switch.c
===================================================================
--- linux-mcount.git.orig/lib/tracing/trace_sched_switch.c 2008-01-23 10:27:31.000000000 -0500
+++ linux-mcount.git/lib/tracing/trace_sched_switch.c 2008-01-23 10:27:39.000000000 -0500
@@ -30,6 +30,11 @@ static notrace void sched_switch_callbac
va_list ap;
int cpu;

+ if (likely(!atomic_read(&trace_record_cmdline)))
+ return;
+
+ tracing_record_cmdline(current);
+
if (likely(!trace_enabled))
return;

@@ -62,6 +67,7 @@ static notrace void sched_switch_reset(s

static notrace void start_sched_trace(struct tracing_trace *tr)
{
+ atomic_inc(&trace_record_cmdline);
sched_switch_reset(tr);
trace_enabled = 1;
}
@@ -69,6 +75,7 @@ static notrace void start_sched_trace(st
static notrace void stop_sched_trace(struct tracing_trace *tr)
{
trace_enabled = 0;
+ atomic_dec(&trace_record_cmdline);
}

static notrace void sched_switch_trace_init(struct tracing_trace *tr)
Index: linux-mcount.git/lib/tracing/tracer.c
===================================================================
--- linux-mcount.git.orig/lib/tracing/tracer.c 2008-01-23 10:27:31.000000000 -0500
+++ linux-mcount.git/lib/tracing/tracer.c 2008-01-23 10:27:39.000000000 -0500
@@ -169,6 +169,88 @@ void tracing_stop_function_trace(void)
unregister_mcount_function(&trace_ops);
}

+#define SAVED_CMDLINES 128
+static unsigned map_pid_to_cmdline[PID_MAX_DEFAULT+1];
+static unsigned map_cmdline_to_pid[SAVED_CMDLINES];
+static char saved_cmdlines[SAVED_CMDLINES][TASK_COMM_LEN];
+static int cmdline_idx;
+static DEFINE_SPINLOCK(trace_cmdline_lock);
+atomic_t trace_record_cmdline;
+atomic_t trace_record_cmdline_disabled;
+
+static void trace_init_cmdlines(void)
+{
+ memset(&map_pid_to_cmdline, -1, sizeof(map_pid_to_cmdline));
+ memset(&map_cmdline_to_pid, -1, sizeof(map_cmdline_to_pid));
+ cmdline_idx = 0;
+}
+
+notrace void trace_stop_cmdline_recording(void);
+
+static void notrace trace_save_cmdline(struct task_struct *tsk)
+{
+ unsigned map;
+ unsigned idx;
+
+ if (!tsk->pid || unlikely(tsk->pid > PID_MAX_DEFAULT))
+ return;
+
+ /*
+ * It's not the end of the world if we don't get
+ * the lock, but we also don't want to spin
+ * nor do we want to disable interrupts,
+ * so if we miss here, then better luck next time.
+ */
+ if (!spin_trylock(&trace_cmdline_lock))
+ return;
+
+ idx = map_pid_to_cmdline[tsk->pid];
+ if (idx >= SAVED_CMDLINES) {
+ idx = (cmdline_idx + 1) % SAVED_CMDLINES;
+
+ map = map_cmdline_to_pid[idx];
+ if (map <= PID_MAX_DEFAULT)
+ map_pid_to_cmdline[map] = (unsigned)-1;
+
+ map_pid_to_cmdline[tsk->pid] = idx;
+
+ cmdline_idx = idx;
+ }
+
+ memcpy(&saved_cmdlines[idx], tsk->comm, TASK_COMM_LEN);
+
+ spin_unlock(&trace_cmdline_lock);
+}
+
+static notrace char *trace_find_cmdline(int pid)
+{
+ char *cmdline = "<...>";
+ unsigned map;
+
+ if (!pid)
+ return "<idle>";
+
+ if (pid > PID_MAX_DEFAULT)
+ goto out;
+
+ map = map_pid_to_cmdline[pid];
+ if (map >= SAVED_CMDLINES)
+ goto out;
+
+ cmdline = saved_cmdlines[map];
+
+ out:
+ return cmdline;
+}
+
+void tracing_record_cmdline(struct task_struct *tsk)
+{
+ if (atomic_read(&trace_record_cmdline_disabled))
+ return;
+
+ trace_save_cmdline(tsk);
+}
+
static inline notrace struct tracing_entry *
tracing_get_trace_entry(struct tracing_trace *tr,
struct tracing_trace_cpu *data)
@@ -210,7 +292,6 @@ tracing_generic_entry_update(struct trac
((pc & HARDIRQ_MASK) ? TRACE_FLAG_HARDIRQ : 0) |
((pc & SOFTIRQ_MASK) ? TRACE_FLAG_SOFTIRQ : 0) |
(need_resched() ? TRACE_FLAG_NEED_RESCHED : 0);
- memcpy(entry->comm, tsk->comm, TASK_COMM_LEN);
}

notrace void tracing_function_trace(struct tracing_trace *tr,
@@ -366,6 +447,8 @@ static void *s_start(struct seq_file *m,
if (!current_trace || current_trace != iter->trace)
return NULL;

+ atomic_inc(&trace_record_cmdline_disabled);
+
/* let the tracer grab locks here if needed */
if (current_trace->start)
current_trace->start(iter);
@@ -393,6 +476,8 @@ static void s_stop(struct seq_file *m, v
{
struct tracing_iterator *iter = m->private;

+ atomic_dec(&trace_record_cmdline_disabled);
+
/* let the tracer release locks here if needed */
if (current_trace && current_trace == iter->trace && iter->trace->stop)
iter->trace->stop(iter);
@@ -521,8 +606,11 @@ static void notrace
lat_print_generic(struct seq_file *m, struct tracing_entry *entry, int cpu)
{
int hardirq, softirq;
+ char *comm;
+
+ comm = trace_find_cmdline(entry->pid);

- seq_printf(m, "%8.8s-%-5d ", entry->comm, entry->pid);
+ seq_printf(m, "%8.8s-%-5d ", comm, entry->pid);
seq_printf(m, "%d", cpu);
seq_printf(m, "%c%c",
(entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' : '.',
@@ -584,9 +672,12 @@ print_lat_fmt(struct seq_file *m, struct
abs_usecs = cycles_to_usecs(entry->t - iter->tr->time_start);

if (verbose) {
+ char *comm;
+
+ comm = trace_find_cmdline(entry->pid);
seq_printf(m, "%16s %5d %d %d %08x %08x [%08lx]"
" %ld.%03ldms (+%ld.%03ldms): ",
- entry->comm,
+ comm,
entry->pid, cpu, entry->flags,
entry->preempt_count, trace_idx,
cycles_to_usecs(entry->t),
@@ -623,6 +714,9 @@ static void notrace print_trace_fmt(stru
unsigned long secs;
int sym_only = !!(trace_flags & TRACE_ITER_SYM_ONLY);
unsigned long long t;
+ char *comm;
+
+ comm = trace_find_cmdline(iter->ent->pid);

t = cycles_to_usecs(iter->ent->t);
usec_rem = do_div(t, 1000000ULL);
@@ -630,7 +724,7 @@ static void notrace print_trace_fmt(stru

seq_printf(m, "[%5lu.%06lu] ", secs, usec_rem);
seq_printf(m, "CPU %d: ", iter->cpu);
- seq_printf(m, "%s:%d ", iter->ent->comm,
+ seq_printf(m, "%s:%d ", comm,
iter->ent->pid);
switch (iter->ent->type) {
case TRACE_FN:
@@ -1164,6 +1258,8 @@ __init static int tracer_alloc_buffers(v

tracer_init_debugfs();

+ trace_init_cmdlines();
+
return 0;

free_buffers:
Index: linux-mcount.git/lib/tracing/tracer.h
===================================================================
--- linux-mcount.git.orig/lib/tracing/tracer.h 2008-01-23 10:27:31.000000000 -0500
+++ linux-mcount.git/lib/tracing/tracer.h 2008-01-23 10:27:39.000000000 -0500
@@ -25,7 +25,6 @@ struct tracing_entry {
char preempt_count; /* assumes PREEMPT_MASK is 8 bits or less */
int pid;
cycle_t t;
- char comm[TASK_COMM_LEN];
union {
struct tracing_function fn;
struct tracing_sched_switch ctx;
@@ -98,13 +97,16 @@ void tracing_sched_switch_trace(struct t
struct task_struct *prev,
struct task_struct *next,
unsigned long flags);
-
+void tracing_record_cmdline(struct task_struct *tsk);

void tracing_start_function_trace(void);
void tracing_stop_function_trace(void);
int register_trace(struct trace_types_struct *type);
void unregister_trace(struct trace_types_struct *type);

+extern atomic_t trace_record_cmdline;
+extern atomic_t trace_record_cmdline_disabled;
+
static inline notrace cycle_t now(void)
{
return get_monotonic_cycles();
--


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