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Subject[RFC PATCH 18/23 -v4] 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 | 12 +++-
lib/tracing/tracer.c | 112 +++++++++++++++++++++++++++++++++++++--
lib/tracing/tracer.h | 5 +
5 files changed, 124 insertions(+), 8 deletions(-)
Index: linux-mcount.git/lib/tracing/Kconfig
===================================================================
--- linux-mcount.git.orig/lib/tracing/Kconfig 2008-01-21 10:03:57.000000000 -0500
+++ linux-mcount.git/lib/tracing/Kconfig 2008-01-21 10:04:54.000000000 -0500
@@ -19,6 +19,7 @@ config FUNCTION_TRACER
default n
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 2008-01-21 09:59:15.000000000 -0500
+++ linux-mcount.git/lib/tracing/trace_function.c 2008-01-21 10:04:54.000000000 -0500
@@ -80,9 +80,11 @@ static void function_trace_ctrl_update(s
if (tr->ctrl ^ val) {
if (val) {
trace_enabled = 1;
+ atomic_inc(&trace_record_cmdline);
register_mcount_function(&trace_ops);
} else {
trace_enabled = 0;
+ atomic_dec(&trace_record_cmdline);
unregister_mcount_function(&trace_ops);
}
tr->ctrl = val;
Index: linux-mcount.git/lib/tracing/trace_sched_switch.c
===================================================================
--- linux-mcount.git.orig/lib/tracing/trace_sched_switch.c 2008-01-21 10:03:57.000000000 -0500
+++ linux-mcount.git/lib/tracing/trace_sched_switch.c 2008-01-21 10:04:54.000000000 -0500
@@ -41,6 +41,9 @@ static notrace void sched_switch_callbac
va_list ap;
int cpu;

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

@@ -49,6 +52,7 @@ static notrace void sched_switch_callbac
next = va_arg(ap, typeof(next));
va_end(ap);

+
raw_local_irq_save(flags);
cpu = raw_smp_processor_id();
data = tr->data[cpu];
@@ -82,10 +86,14 @@ static void sched_switch_trace_ctrl_upda
sched_switch_reset(tr);

if (tr->ctrl ^ val) {
- if (val)
+ if (val) {
+ atomic_inc(&trace_record_cmdline);
trace_enabled = 1;
- else
+ } else {
trace_enabled = 0;
+ atomic_dec(&trace_record_cmdline);
+ }
+
tr->ctrl = val;
}
}
Index: linux-mcount.git/lib/tracing/tracer.c
===================================================================
--- linux-mcount.git.orig/lib/tracing/tracer.c 2008-01-21 10:03:57.000000000 -0500
+++ linux-mcount.git/lib/tracing/tracer.c 2008-01-21 10:04:54.000000000 -0500
@@ -49,6 +49,88 @@ void notrace tracing_reset(struct tracin
atomic_set(&data->underrun, 0);
}

+#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)
@@ -90,7 +172,6 @@ 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,
@@ -242,6 +323,8 @@ static void *s_start(struct seq_file *m,
loff_t l = 0;
int i;

+ atomic_inc(&trace_record_cmdline_disabled);
+
/* let the tracer grab locks here if needed */
if (iter->tr->start)
iter->tr->start(iter);
@@ -269,6 +352,8 @@ 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 (iter->tr->stop)
iter->tr->stop(iter);
@@ -390,8 +475,11 @@ static void notrace
lat_print_generic(struct seq_file *m, struct tracing_entry *entry, int cpu)
{
int hardirq, softirq;
+ char *comm;

- seq_printf(m, "%8.8s-%-5d ", entry->comm, entry->pid);
+ comm = trace_find_cmdline(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' : '.',
@@ -453,9 +541,12 @@ 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),
@@ -492,6 +583,9 @@ 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);
@@ -499,7 +593,7 @@ 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:
@@ -813,6 +907,14 @@ static __init int trace_init_debugfs(voi
return 0;
}

-device_initcall(trace_init_debugfs);
+static __init int trace_init(void)
+{
+ trace_init_cmdlines();
+
+ return trace_init_debugfs();
+
+}
+
+device_initcall(trace_init);

#endif /* CONFIG_DEBUG_FS */
Index: linux-mcount.git/lib/tracing/tracer.h
===================================================================
--- linux-mcount.git.orig/lib/tracing/tracer.h 2008-01-21 10:03:57.000000000 -0500
+++ linux-mcount.git/lib/tracing/tracer.h 2008-01-21 10:04:54.000000000 -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;
@@ -91,6 +90,10 @@ 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);
+
+extern atomic_t trace_record_cmdline;
+extern atomic_t trace_record_cmdline_disabled;

extern struct file_operations tracing_fops;
extern struct file_operations tracing_lt_fops;
--


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