On Tue, Jun 11, 2019 at 09:10:46PM +0200, Mark Kettenis wrote:
> 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.
Ignoring taskletq and systq use in burner_task/switchtask across
drivers and the local only backlight_schedule_update_status(), was it
intentional to exclude:
workqueue.h: alloc_workqueue()
struct taskq *tq = taskq_create(name, 1, IPL_TTY, 0);
workqueue.h: alloc_ordered_workqueue()
struct taskq *tq = taskq_create(name, 1, IPL_TTY, 0);
workqueue.h:
#define system_power_efficient_wq ((struct workqueue_struct *)systq)
>
> 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);
>
>
