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Message-ID: <20080210072054.GO4100@elte.hu>
Date: Sun, 10 Feb 2008 08:20:54 +0100
From: Ingo Molnar <mingo@...e.hu>
To: linux-kernel@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@....com.au>,
Steven Rostedt <rostedt@...dmis.org>
Subject: [14/19] ftrace: tracer for scheduler wakeup latency
From: Steven Rostedt <srostedt@...hat.com>
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
--------------------------------------------------------------------
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: Steven Rostedt <srostedt@...hat.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
include/linux/ftrace.h | 23 ++
kernel/trace/Kconfig | 13 +
kernel/trace/Makefile | 1
kernel/trace/trace_sched_wakeup.c | 310 ++++++++++++++++++++++++++++++++++++++
4 files changed, 343 insertions(+), 4 deletions(-)
Index: linux/include/linux/ftrace.h
===================================================================
--- linux.orig/include/linux/ftrace.h
+++ linux/include/linux/ftrace.h
@@ -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 */
Index: linux/kernel/trace/Kconfig
===================================================================
--- linux.orig/kernel/trace/Kconfig
+++ linux/kernel/trace/Kconfig
@@ -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
Index: linux/kernel/trace/Makefile
===================================================================
--- linux.orig/kernel/trace/Makefile
+++ linux/kernel/trace/Makefile
@@ -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
Index: linux/kernel/trace/trace_sched_wakeup.c
===================================================================
--- /dev/null
+++ linux/kernel/trace/trace_sched_wakeup.c
@@ -0,0 +1,310 @@
+/*
+ * trace task wakeup timings
+ *
+ * Copyright (C) 2007-2008 Steven Rostedt <srostedt@...hat.com>
+ * Copyright (C) 2008 Ingo Molnar <mingo@...hat.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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