sched/deadline: Add latency tracing for SCHED_DEADLINE tasks

It is very likely that systems that wants/needs to use the new
SCHED_DEADLINE policy also want to have the scheduling latency of
the -deadline tasks under control.

For this reason a new version of the scheduling wakeup latency,
called "wakeup_dl", is introduced.

As a consequence of applying this patch there will be three wakeup
latency tracer:

 * "wakeup", that deals with all tasks in the system;
 * "wakeup_rt", that deals with -rt and -deadline tasks only;
 * "wakeup_dl", that deals with -deadline tasks only.

Signed-off-by: Dario Faggioli <raistlin@linux.it>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-9-git-send-email-juri.lelli@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 79 insertions, 18 deletions

diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index fee77e15d815..090c4d9dcf16 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -27,6 +27,8 @@ static int			wakeup_cpu;
 static int                      wakeup_current_cpu;
 static unsigned                 wakeup_prio = -1;
 static int                      wakeup_rt;
+static int                      wakeup_dl;
+static int                      tracing_dl = 0;
 
 static arch_spinlock_t wakeup_lock =
         (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
@@ -437,6 +439,7 @@ static void __wakeup_reset(struct trace_array *tr)
 {
         wakeup_cpu = -1;
         wakeup_prio = -1;
+        tracing_dl = 0;
 
         if (wakeup_task)
                 put_task_struct(wakeup_task);
@@ -472,9 +475,17 @@ probe_wakeup(void *ignore, struct task_struct *p, int success)
         tracing_record_cmdline(p);
         tracing_record_cmdline(current);
 
-        if ((wakeup_rt && !rt_task(p)) ||
-                        p->prio >= wakeup_prio ||
-                        p->prio >= current->prio)
+        /*
+         * Semantic is like this:
+         *  - wakeup tracer handles all tasks in the system, independently
+         *    from their scheduling class;
+         *  - wakeup_rt tracer handles tasks belonging to sched_dl and
+         *    sched_rt class;
+         *  - wakeup_dl handles tasks belonging to sched_dl class only.
+         */
+        if (tracing_dl || (wakeup_dl && !dl_task(p)) ||
+            (wakeup_rt && !dl_task(p) && !rt_task(p)) ||
+            (!dl_task(p) && (p->prio >= wakeup_prio || p->prio >= current->prio)))
                 return;
 
         pc = preempt_count();
@@ -486,7 +497,8 @@ probe_wakeup(void *ignore, struct task_struct *p, int success)
         arch_spin_lock(&wakeup_lock);
 
         /* check for races. */
-        if (!tracer_enabled || p->prio >= wakeup_prio)
+        if (!tracer_enabled || tracing_dl ||
+            (!dl_task(p) && p->prio >= wakeup_prio))
                 goto out_locked;
 
         /* reset the trace */
@@ -496,6 +508,15 @@ probe_wakeup(void *ignore, struct task_struct *p, int success)
         wakeup_current_cpu = wakeup_cpu;
         wakeup_prio = p->prio;
 
+        /*
+         * Once you start tracing a -deadline task, don't bother tracing
+         * another task until the first one wakes up.
+         */
+        if (dl_task(p))
+                tracing_dl = 1;
+        else
+                tracing_dl = 0;
+
         wakeup_task = p;
         get_task_struct(wakeup_task);
 
@@ -597,16 +618,25 @@ static int __wakeup_tracer_init(struct trace_array *tr)
 
 static int wakeup_tracer_init(struct trace_array *tr)
 {
+        wakeup_dl = 0;
         wakeup_rt = 0;
         return __wakeup_tracer_init(tr);
 }
 
 static int wakeup_rt_tracer_init(struct trace_array *tr)
 {
+        wakeup_dl = 0;
         wakeup_rt = 1;
         return __wakeup_tracer_init(tr);
 }
 
+static int wakeup_dl_tracer_init(struct trace_array *tr)
+{
+        wakeup_dl = 1;
+        wakeup_rt = 0;
+        return __wakeup_tracer_init(tr);
+}
+
 static void wakeup_tracer_reset(struct trace_array *tr)
 {
         int lat_flag = save_flags & TRACE_ITER_LATENCY_FMT;
@@ -674,6 +704,28 @@ static struct tracer wakeup_rt_tracer __read_mostly =
         .use_max_tr     = true,
 };
 
+static struct tracer wakeup_dl_tracer __read_mostly =
+{
+        .name           = "wakeup_dl",
+        .init           = wakeup_dl_tracer_init,
+        .reset          = wakeup_tracer_reset,
+        .start          = wakeup_tracer_start,
+        .stop           = wakeup_tracer_stop,
+        .wait_pipe      = poll_wait_pipe,
+        .print_max      = true,
+        .print_header   = wakeup_print_header,
+        .print_line     = wakeup_print_line,
+        .flags          = &tracer_flags,
+        .set_flag       = wakeup_set_flag,
+        .flag_changed   = wakeup_flag_changed,
+#ifdef CONFIG_FTRACE_SELFTEST
+        .selftest    = trace_selftest_startup_wakeup,
+#endif
+        .open           = wakeup_trace_open,
+        .close          = wakeup_trace_close,
+        .use_max_tr     = true,
+};
+
 __init static int init_wakeup_tracer(void)
 {
         int ret;
@@ -686,6 +738,10 @@ __init static int init_wakeup_tracer(void)
         if (ret)
                 return ret;
 
+        ret = register_tracer(&wakeup_dl_tracer);
+        if (ret)
+                return ret;
+
         return 0;
 }
 core_initcall(init_wakeup_tracer);
diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index a7329b7902f8..e98fca60974f 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -1022,11 +1022,16 @@ trace_selftest_startup_nop(struct tracer *trace, struct trace_array *tr)
 #ifdef CONFIG_SCHED_TRACER
 static int trace_wakeup_test_thread(void *data)
 {
-        /* Make this a RT thread, doesn't need to be too high */
-        static const struct sched_param param = { .sched_priority = 5 };
+        /* Make this a -deadline thread */
+        static const struct sched_attr attr = {
+                .sched_policy = SCHED_DEADLINE,
+                .sched_runtime = 100000ULL,
+                .sched_deadline = 10000000ULL,
+                .sched_period = 10000000ULL
+        };
         struct completion *x = data;
 
-        sched_setscheduler(current, SCHED_FIFO, &param);
+        sched_setattr(current, &attr);
 
         /* Make it know we have a new prio */
         complete(x);
@@ -1040,8 +1045,8 @@ static int trace_wakeup_test_thread(void *data)
         /* we are awake, now wait to disappear */
         while (!kthread_should_stop()) {
                 /*
-                 * This is an RT task, do short sleeps to let
-                 * others run.
+                 * This will likely be the system top priority
+                 * task, do short sleeps to let others run.
                  */
                 msleep(100);
         }
@@ -1054,21 +1059,21 @@ trace_selftest_startup_wakeup(struct tracer *trace, struct trace_array *tr)
 {
         unsigned long save_max = tracing_max_latency;
         struct task_struct *p;
-        struct completion isrt;
+        struct completion is_ready;
         unsigned long count;
         int ret;
 
-        init_completion(&isrt);
+        init_completion(&is_ready);
 
-        /* create a high prio thread */
-        p = kthread_run(trace_wakeup_test_thread, &isrt, "ftrace-test");
+        /* create a -deadline thread */
+        p = kthread_run(trace_wakeup_test_thread, &is_ready, "ftrace-test");
         if (IS_ERR(p)) {
                 printk(KERN_CONT "Failed to create ftrace wakeup test thread ");
                 return -1;
         }
 
-        /* make sure the thread is running at an RT prio */
-        wait_for_completion(&isrt);
+        /* make sure the thread is running at -deadline policy */
+        wait_for_completion(&is_ready);
 
         /* start the tracing */
         ret = tracer_init(trace, tr);
@@ -1082,19 +1087,19 @@ trace_selftest_startup_wakeup(struct tracer *trace, struct trace_array *tr)
 
         while (p->on_rq) {
                 /*
-                 * Sleep to make sure the RT thread is asleep too.
+                 * Sleep to make sure the -deadline thread is asleep too.
                  * On virtual machines we can't rely on timings,
                  * but we want to make sure this test still works.
                  */
                 msleep(100);
         }
 
-        init_completion(&isrt);
+        init_completion(&is_ready);
 
         wake_up_process(p);
 
         /* Wait for the task to wake up */
-        wait_for_completion(&isrt);
+        wait_for_completion(&is_ready);
 
         /* stop the tracing. */
         tracing_stop();