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Subject[PATCH 08/14] sched: add latency tracing for -deadline tasks.
Date
From: Dario Faggioli <raistlin@linux.it>

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>
---
kernel/trace/trace_sched_wakeup.c | 44 +++++++++++++++++++++++++++++++++----
kernel/trace/trace_selftest.c | 28 +++++++++++++----------
2 files changed, 57 insertions(+), 15 deletions(-)
diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index 9fe45fc..0a63eab 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -27,6 +27,7 @@ static int wakeup_cpu;
static int wakeup_current_cpu;
static unsigned wakeup_prio = -1;
static int wakeup_rt;
+static int wakeup_dl;

static arch_spinlock_t wakeup_lock =
(arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
@@ -429,9 +430,17 @@ 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 ((wakeup_dl && !dl_task(p)) ||
+ (wakeup_rt && !dl_task(p) && !rt_task(p)) ||
+ (p->prio >= wakeup_prio || p->prio >= current->prio))
return;

pc = preempt_count();
@@ -443,7 +452,7 @@ 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 || (!dl_task(p) && p->prio >= wakeup_prio))
goto out_locked;

/* reset the trace */
@@ -551,16 +560,25 @@ 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)
{
stop_wakeup_tracer(tr);
@@ -623,6 +641,20 @@ 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 = 1,
+#ifdef CONFIG_FTRACE_SELFTEST
+ .selftest = trace_selftest_startup_wakeup,
+#endif
+};
+
__init static int init_wakeup_tracer(void)
{
int ret;
@@ -635,6 +667,10 @@ __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 4762316..c15c445 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -1016,11 +1016,17 @@ 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 */
+ struct sched_param2 paramx = {
+ .sched_priority = 0,
+ .sched_runtime = 100000ULL,
+ .sched_deadline = 10000000ULL,
+ .sched_period = 10000000ULL
+ .sched_flags = 0
+ };
struct completion *x = data;

- sched_setscheduler(current, SCHED_FIFO, &param);
+ sched_setscheduler2(current, SCHED_DEADLINE, &paramx);

/* Make it know we have a new prio */
complete(x);
@@ -1034,8 +1040,8 @@ 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);
}
@@ -1048,21 +1054,21 @@ 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);
--
1.7.9.5


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