Commit 352ad25a authored by Steven Rostedt's avatar Steven Rostedt Committed by Thomas Gleixner
Browse files

ftrace: tracer for scheduler wakeup latency



This patch adds the tracer that tracks the wakeup latency of the
highest priority waking task.

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

Also added to /debugfs/tracing

  tracing_max_latency
     holds the current max latency for the wakeup

  wakeup_thresh
     if set to other than zero, a log will be recorded
     for every wakeup that takes longer than the number
     entered in here (usecs for all counters)
     (deletes previous trace)

Examples:

  (with ftrace_enabled = 0)

============
preemption latency trace v1.1.5 on 2.6.24-rc8
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
--------------------------------------------------------------------
 latency: 26 us, #2/2, CPU#1 | (M:rt VP:0, KP:0, SP:0 HP:0 #P:2)
    -----------------
    | task: migration/0-3 (uid:0 nice:-5 policy:1 rt_prio:99)
    -----------------

                 _------=> CPU#
                / _-----=> irqs-off
               | / _----=> need-resched
               || / _---=> hardirq/softirq
               ||| / _--=> preempt-depth
               |||| /
               |||||     delay
   cmd     pid ||||| time  |   caller
      \   /    |||||   \   |   /
   quilt-8551  0d..3    0us+: wake_up_process+0x15/0x17 <ffffffff80233e80> (sched_exec+0xc9/0x100 <ffffffff80235343>)
   quilt-8551  0d..4   26us : sched_switch_callback+0x73/0x81 <ffffffff80338d2f> (schedule+0x483/0x6d5 <ffffffff8048b3ee>)

vim:ft=help
============

  (with ftrace_enabled = 1)

============
preemption latency trace v1.1.5 on 2.6.24-rc8
--------------------------------------------------------------------
 latency: 36 us, #45/45, CPU#0 | (M:rt VP:0, KP:0, SP:0 HP:0 #P:2)
    -----------------
    | task: migration/1-5 (uid:0 nice:-5 policy:1 rt_prio:99)
    -----------------

                 _------=> CPU#
                / _-----=> irqs-off
               | / _----=> need-resched
               || / _---=> hardirq/softirq
               ||| / _--=> preempt-depth
               |||| /
               |||||     delay
   cmd     pid ||||| time  |   caller
      \   /    |||||   \   |   /
    bash-10653 1d..3    0us : wake_up_process+0x15/0x17 <ffffffff80233e80> (sched_exec+0xc9/0x100 <ffffffff80235343>)
    bash-10653 1d..3    1us : try_to_wake_up+0x271/0x2e7 <ffffffff80233dcf> (sub_preempt_count+0xc/0x7a <ffffffff8023309e>)
    bash-10653 1d..2    2us : try_to_wake_up+0x296/0x2e7 <ffffffff80233df4> (update_rq_clock+0x9/0x20 <ffffffff802303f3>)
    bash-10653 1d..2    2us : update_rq_clock+0x1e/0x20 <ffffffff80230408> (__update_rq_clock+0xc/0x90 <ffffffff80230366>)
    bash-10653 1d..2    3us : __update_rq_clock+0x1b/0x90 <ffffffff80230375> (sched_clock+0x9/0x29 <ffffffff80214529>)
    bash-10653 1d..2    4us : try_to_wake_up+0x2a6/0x2e7 <ffffffff80233e04> (activate_task+0xc/0x3f <ffffffff8022ffca>)
    bash-10653 1d..2    4us : activate_task+0x2d/0x3f <ffffffff8022ffeb> (enqueue_task+0xe/0x66 <ffffffff8022ff66>)
    bash-10653 1d..2    5us : enqueue_task+0x5b/0x66 <ffffffff8022ffb3> (enqueue_task_rt+0x9/0x3c <ffffffff80233351>)
    bash-10653 1d..2    6us : try_to_wake_up+0x2ba/0x2e7 <ffffffff80233e18> (check_preempt_wakeup+0x12/0x99 <ffffffff80234f84>)
[...]
    bash-10653 1d..5   33us : tracing_record_cmdline+0xcf/0xd4 <ffffffff80338aad> (_spin_unlock+0x9/0x33 <ffffffff8048d3ec>)
    bash-10653 1d..5   34us : _spin_unlock+0x19/0x33 <ffffffff8048d3fc> (sub_preempt_count+0xc/0x7a <ffffffff8023309e>)
    bash-10653 1d..4   35us : wakeup_sched_switch+0x65/0x2ff <ffffffff80339f66> (_spin_lock_irqsave+0xc/0xa9 <ffffffff8048d08b>)
    bash-10653 1d..4   35us : _spin_lock_irqsave+0x19/0xa9 <ffffffff8048d098> (add_preempt_count+0xe/0x77 <ffffffff8023311a>)
    bash-10653 1d..4   36us : sched_switch_callback+0x73/0x81 <ffffffff80338d2f> (schedule+0x483/0x6d5 <ffffffff8048b3ee>)

vim:ft=help
============

The [...] was added here to not waste your email box space.
Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 35e8e302
......@@ -5,10 +5,6 @@
#include <linux/linkage.h>
#define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
#define CALLER_ADDR1 ((unsigned long)__builtin_return_address(1))
#define CALLER_ADDR2 ((unsigned long)__builtin_return_address(2))
typedef void (*ftrace_func_t)(unsigned long ip, unsigned long parent_ip);
struct ftrace_ops {
......@@ -35,4 +31,23 @@ extern void mcount(void);
# define unregister_ftrace_function(ops) do { } while (0)
# define clear_ftrace_function(ops) do { } while (0)
#endif /* CONFIG_FTRACE */
#ifdef CONFIG_FRAME_POINTER
/* TODO: need to fix this for ARM */
# define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
# define CALLER_ADDR1 ((unsigned long)__builtin_return_address(1))
# define CALLER_ADDR2 ((unsigned long)__builtin_return_address(2))
# define CALLER_ADDR3 ((unsigned long)__builtin_return_address(3))
# define CALLER_ADDR4 ((unsigned long)__builtin_return_address(4))
# define CALLER_ADDR5 ((unsigned long)__builtin_return_address(5))
#else
# define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
# define CALLER_ADDR1 0UL
# define CALLER_ADDR2 0UL
# define CALLER_ADDR3 0UL
# define CALLER_ADDR4 0UL
# define CALLER_ADDR5 0UL
#endif
#endif /* _LINUX_FTRACE_H */
......@@ -4,6 +4,9 @@
config HAVE_FTRACE
bool
config TRACER_MAX_TRACE
bool
config TRACING
bool
select DEBUG_FS
......@@ -23,6 +26,16 @@ config FTRACE
(the bootup default), then the overhead of the instructions is very
small and not measurable even in micro-benchmarks.
config SCHED_TRACER
bool "Scheduling Latency Tracer"
depends on DEBUG_KERNEL
select TRACING
select CONTEXT_SWITCH_TRACER
select TRACER_MAX_TRACE
help
This tracer tracks the latency of the highest priority task
to be scheduled in, starting from the point it has woken up.
config CONTEXT_SWITCH_TRACER
bool "Trace process context switches"
depends on DEBUG_KERNEL
......
......@@ -3,5 +3,6 @@ obj-$(CONFIG_FTRACE) += libftrace.o
obj-$(CONFIG_TRACING) += trace.o
obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o
obj-$(CONFIG_FTRACE) += trace_functions.o
obj-$(CONFIG_SCHED_TRACER) += trace_sched_wakeup.o
libftrace-y := ftrace.o
/*
* trace task wakeup timings
*
* Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
* Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
*
* Based on code from the latency_tracer, that is:
*
* Copyright (C) 2004-2006 Ingo Molnar
* Copyright (C) 2004 William Lee Irwin III
*/
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/debugfs.h>
#include <linux/kallsyms.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include "trace.h"
static struct trace_array *wakeup_trace;
static int __read_mostly tracer_enabled;
static struct task_struct *wakeup_task;
static int wakeup_cpu;
static unsigned wakeup_prio = -1;
static DEFINE_SPINLOCK(wakeup_lock);
static void notrace __wakeup_reset(struct trace_array *tr);
/*
* Should this new latency be reported/recorded?
*/
static int notrace report_latency(cycle_t delta)
{
if (tracing_thresh) {
if (delta < tracing_thresh)
return 0;
} else {
if (delta <= tracing_max_latency)
return 0;
}
return 1;
}
void notrace
wakeup_sched_switch(struct task_struct *prev, struct task_struct *next)
{
unsigned long latency = 0, t0 = 0, t1 = 0;
struct trace_array *tr = wakeup_trace;
struct trace_array_cpu *data;
cycle_t T0, T1, delta;
unsigned long flags;
long disabled;
int cpu;
if (unlikely(!tracer_enabled))
return;
/*
* When we start a new trace, we set wakeup_task to NULL
* and then set tracer_enabled = 1. We want to make sure
* that another CPU does not see the tracer_enabled = 1
* and the wakeup_task with an older task, that might
* actually be the same as next.
*/
smp_rmb();
if (next != wakeup_task)
return;
/* The task we are waitng for is waking up */
data = tr->data[wakeup_cpu];
/* disable local data, not wakeup_cpu data */
cpu = raw_smp_processor_id();
disabled = atomic_inc_return(&tr->data[cpu]->disabled);
if (likely(disabled != 1))
goto out;
spin_lock_irqsave(&wakeup_lock, flags);
/* We could race with grabbing wakeup_lock */
if (unlikely(!tracer_enabled || next != wakeup_task))
goto out_unlock;
ftrace(tr, data, CALLER_ADDR1, CALLER_ADDR2, flags);
/*
* usecs conversion is slow so we try to delay the conversion
* as long as possible:
*/
T0 = data->preempt_timestamp;
T1 = now(cpu);
delta = T1-T0;
if (!report_latency(delta))
goto out_unlock;
latency = nsecs_to_usecs(delta);
tracing_max_latency = delta;
t0 = nsecs_to_usecs(T0);
t1 = nsecs_to_usecs(T1);
update_max_tr(tr, wakeup_task, wakeup_cpu);
if (tracing_thresh) {
printk(KERN_INFO "(%16s-%-5d|#%d): %lu us wakeup latency "
"violates %lu us threshold.\n"
" => started at timestamp %lu: ",
wakeup_task->comm, wakeup_task->pid,
raw_smp_processor_id(),
latency, nsecs_to_usecs(tracing_thresh), t0);
} else {
printk(KERN_INFO "(%16s-%-5d|#%d): new %lu us maximum "
"wakeup latency.\n => started at timestamp %lu: ",
wakeup_task->comm, wakeup_task->pid,
cpu, latency, t0);
}
printk(KERN_CONT " ended at timestamp %lu: ", t1);
dump_stack();
t1 = nsecs_to_usecs(now(cpu));
printk(KERN_CONT " dump-end timestamp %lu\n\n", t1);
out_unlock:
__wakeup_reset(tr);
spin_unlock_irqrestore(&wakeup_lock, flags);
out:
atomic_dec(&tr->data[cpu]->disabled);
}
static void notrace __wakeup_reset(struct trace_array *tr)
{
struct trace_array_cpu *data;
int cpu;
assert_spin_locked(&wakeup_lock);
for_each_possible_cpu(cpu) {
data = tr->data[cpu];
tracing_reset(data);
}
wakeup_cpu = -1;
wakeup_prio = -1;
if (wakeup_task)
put_task_struct(wakeup_task);
wakeup_task = NULL;
}
static void notrace wakeup_reset(struct trace_array *tr)
{
unsigned long flags;
spin_lock_irqsave(&wakeup_lock, flags);
__wakeup_reset(tr);
spin_unlock_irqrestore(&wakeup_lock, flags);
}
static notrace void
wakeup_check_start(struct trace_array *tr, struct task_struct *p,
struct task_struct *curr)
{
int cpu = smp_processor_id();
unsigned long flags;
long disabled;
if (likely(!rt_task(p)) ||
p->prio >= wakeup_prio ||
p->prio >= curr->prio)
return;
disabled = atomic_inc_return(&tr->data[cpu]->disabled);
if (unlikely(disabled != 1))
goto out;
/* interrupts should be off from try_to_wake_up */
spin_lock(&wakeup_lock);
/* check for races. */
if (!tracer_enabled || p->prio >= wakeup_prio)
goto out_locked;
/* reset the trace */
__wakeup_reset(tr);
wakeup_cpu = task_cpu(p);
wakeup_prio = p->prio;
wakeup_task = p;
get_task_struct(wakeup_task);
local_save_flags(flags);
tr->data[wakeup_cpu]->preempt_timestamp = now(cpu);
ftrace(tr, tr->data[wakeup_cpu], CALLER_ADDR1, CALLER_ADDR2, flags);
out_locked:
spin_unlock(&wakeup_lock);
out:
atomic_dec(&tr->data[cpu]->disabled);
}
notrace void
ftrace_wake_up_task(struct task_struct *wakee, struct task_struct *curr)
{
if (likely(!tracer_enabled))
return;
wakeup_check_start(wakeup_trace, wakee, curr);
}
notrace void
ftrace_wake_up_new_task(struct task_struct *wakee, struct task_struct *curr)
{
if (likely(!tracer_enabled))
return;
wakeup_check_start(wakeup_trace, wakee, curr);
}
static notrace void start_wakeup_tracer(struct trace_array *tr)
{
wakeup_reset(tr);
/*
* Don't let the tracer_enabled = 1 show up before
* the wakeup_task is reset. This may be overkill since
* wakeup_reset does a spin_unlock after setting the
* wakeup_task to NULL, but I want to be safe.
* This is a slow path anyway.
*/
smp_wmb();
tracer_enabled = 1;
return;
}
static notrace void stop_wakeup_tracer(struct trace_array *tr)
{
tracer_enabled = 0;
}
static notrace void wakeup_tracer_init(struct trace_array *tr)
{
wakeup_trace = tr;
if (tr->ctrl)
start_wakeup_tracer(tr);
}
static notrace void wakeup_tracer_reset(struct trace_array *tr)
{
if (tr->ctrl) {
stop_wakeup_tracer(tr);
/* make sure we put back any tasks we are tracing */
wakeup_reset(tr);
}
}
static void wakeup_tracer_ctrl_update(struct trace_array *tr)
{
if (tr->ctrl)
start_wakeup_tracer(tr);
else
stop_wakeup_tracer(tr);
}
static void notrace wakeup_tracer_open(struct trace_iterator *iter)
{
/* stop the trace while dumping */
if (iter->tr->ctrl)
stop_wakeup_tracer(iter->tr);
}
static void notrace wakeup_tracer_close(struct trace_iterator *iter)
{
/* forget about any processes we were recording */
if (iter->tr->ctrl)
start_wakeup_tracer(iter->tr);
}
static struct tracer wakeup_tracer __read_mostly =
{
.name = "wakeup",
.init = wakeup_tracer_init,
.reset = wakeup_tracer_reset,
.open = wakeup_tracer_open,
.close = wakeup_tracer_close,
.ctrl_update = wakeup_tracer_ctrl_update,
.print_max = 1,
};
__init static int init_wakeup_tracer(void)
{
int ret;
ret = register_tracer(&wakeup_tracer);
if (ret)
return ret;
return 0;
}
device_initcall(init_wakeup_tracer);
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