The drm(4) codebase really needs multi-threaded task queues since the
code has taks that wait for the completion of other tasks that are
submitted to the same task queue. Thank you Linux...
Unfortunately the code also needs to wait for the completion of
submitted tasks from other threads. This implemented using
task_barrier(9). But unfortunately our current implementation only
works for single-threaded task queues.
The diff below fixes this by marking the barrier task with a flag and
making sure that all threads of the task queue are syncchronized.
This achived through a TASK_BARRIER flag that simply blocks the
threads until the last unblocked thread sees the flag and executes the
task.
The diff also starts 4 threads for each workqueue that gets created by
the drm(4) layer. The number 4 is a bit arbitrary but it is the
number of threads that Linux creates per CPU for a so-called "unbound"
workqueue which hopefully is enough to always make progress.
Please test. If you experience a "hang" with this diff, please try to
log in to the machine remotely over ssh and send me and jsg@ the
output of "ps -AHwlk".
Thanks,
Mark
Index: dev/pci/drm/drm_linux.c
===================================================================
RCS file: /cvs/src/sys/dev/pci/drm/drm_linux.c,v
retrieving revision 1.38
diff -u -p -r1.38 drm_linux.c
--- dev/pci/drm/drm_linux.c 9 Jun 2019 12:58:30 -0000 1.38
+++ dev/pci/drm/drm_linux.c 11 Jun 2019 18:54:38 -0000
@@ -1399,15 +1399,15 @@ drm_linux_init(void)
{
if (system_wq == NULL) {
system_wq = (struct workqueue_struct *)
- taskq_create("drmwq", 1, IPL_HIGH, 0);
+ taskq_create("drmwq", 4, IPL_HIGH, 0);
}
if (system_unbound_wq == NULL) {
system_unbound_wq = (struct workqueue_struct *)
- taskq_create("drmubwq", 1, IPL_HIGH, 0);
+ taskq_create("drmubwq", 4, IPL_HIGH, 0);
}
if (system_long_wq == NULL) {
system_long_wq = (struct workqueue_struct *)
- taskq_create("drmlwq", 1, IPL_HIGH, 0);
+ taskq_create("drmlwq", 4, IPL_HIGH, 0);
}
if (taskletq == NULL)
Index: dev/pci/drm/i915/intel_hotplug.c
===================================================================
RCS file: /cvs/src/sys/dev/pci/drm/i915/intel_hotplug.c,v
retrieving revision 1.2
diff -u -p -r1.2 intel_hotplug.c
--- dev/pci/drm/i915/intel_hotplug.c 14 Apr 2019 10:14:52 -0000 1.2
+++ dev/pci/drm/i915/intel_hotplug.c 11 Jun 2019 18:54:38 -0000
@@ -619,7 +619,6 @@ void intel_hpd_init_work(struct drm_i915
INIT_WORK(&dev_priv->hotplug.hotplug_work, i915_hotplug_work_func);
INIT_WORK(&dev_priv->hotplug.dig_port_work, i915_digport_work_func);
INIT_WORK(&dev_priv->hotplug.poll_init_work, i915_hpd_poll_init_work);
- dev_priv->hotplug.poll_init_work.tq = systq;
INIT_DELAYED_WORK(&dev_priv->hotplug.reenable_work,
intel_hpd_irq_storm_reenable_work);
}
Index: kern/kern_task.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_task.c,v
retrieving revision 1.25
diff -u -p -r1.25 kern_task.c
--- kern/kern_task.c 28 Apr 2019 04:20:40 -0000 1.25
+++ kern/kern_task.c 11 Jun 2019 18:54:39 -0000
@@ -43,6 +43,7 @@ struct taskq {
TQ_S_DESTROYED
} tq_state;
unsigned int tq_running;
+ unsigned int tq_barrier;
unsigned int tq_nthreads;
unsigned int tq_flags;
const char *tq_name;
@@ -59,6 +60,7 @@ static const char taskq_sys_name[] = "sy
struct taskq taskq_sys = {
TQ_S_CREATED,
0,
+ 0,
1,
0,
taskq_sys_name,
@@ -77,6 +79,7 @@ static const char taskq_sys_mp_name[] =
struct taskq taskq_sys_mp = {
TQ_S_CREATED,
0,
+ 0,
1,
TASKQ_MPSAFE,
taskq_sys_mp_name,
@@ -122,6 +125,7 @@ taskq_create(const char *name, unsigned
tq->tq_state = TQ_S_CREATED;
tq->tq_running = 0;
+ tq->tq_barrier = 0;
tq->tq_nthreads = nthreads;
tq->tq_name = name;
tq->tq_flags = flags;
@@ -161,6 +165,7 @@ taskq_destroy(struct taskq *tq)
panic("unexpected %s tq state %u", tq->tq_name, tq->tq_state);
}
+ tq->tq_barrier = 0;
while (tq->tq_running > 0) {
wakeup(tq);
msleep(&tq->tq_running, &tq->tq_mtx, PWAIT, "tqdestroy", 0);
@@ -223,6 +228,7 @@ taskq_barrier(struct taskq *tq)
WITNESS_CHECKORDER(&tq->tq_lock_object, LOP_NEWORDER, NULL);
+ SET(t.t_flags, TASK_BARRIER);
task_add(tq, &t);
cond_wait(&c, "tqbar");
}
@@ -238,6 +244,7 @@ taskq_del_barrier(struct taskq *tq, stru
if (task_del(tq, del))
return;
+ SET(t.t_flags, TASK_BARRIER);
task_add(tq, &t);
cond_wait(&c, "tqbar");
}
@@ -304,6 +311,7 @@ taskq_next_work(struct taskq *tq, struct
struct task *next;
mtx_enter(&tq->tq_mtx);
+retry:
while ((next = TAILQ_FIRST(&tq->tq_worklist)) == NULL) {
if (tq->tq_state != TQ_S_RUNNING) {
mtx_leave(&tq->tq_mtx);
@@ -311,6 +319,17 @@ taskq_next_work(struct taskq *tq, struct
}
msleep(tq, &tq->tq_mtx, PWAIT, "bored", 0);
+ }
+
+ if (ISSET(next->t_flags, TASK_BARRIER)) {
+ if (++tq->tq_barrier == tq->tq_nthreads) {
+ tq->tq_barrier = 0;
+ wakeup(tq);
+ } else {
+ while (tq->tq_barrier > 0)
+ msleep(tq, &tq->tq_mtx, PWAIT, "tqblk", 0);
+ goto retry;
+ }
}
TAILQ_REMOVE(&tq->tq_worklist, next, t_entry);
Index: sys/task.h
===================================================================
RCS file: /cvs/src/sys/sys/task.h,v
retrieving revision 1.15
diff -u -p -r1.15 task.h
--- sys/task.h 28 Apr 2019 04:20:40 -0000 1.15
+++ sys/task.h 11 Jun 2019 18:54:39 -0000
@@ -31,6 +31,7 @@ struct task {
};
#define TASK_ONQUEUE 1
+#define TASK_BARRIER 2
TAILQ_HEAD(task_list, task);
