On 11/15/2018 12:33 AM, Koenig, Christian wrote:
Am 14.11.18 um 18:29 schrieb Sharat Masetty:
On 11/8/2018 8:11 PM, Koenig, Christian wrote:
Am 08.11.18 um 14:42 schrieb Sharat Masetty:
Hi Christian,
Can you please review this patch? It is a continuation of the
discussion at [1].
At first I was thinking of using a cancel for suspend instead of a
mod(to an
arbitrarily large value), but I couldn't get it to fit in as I have
an additional
constraint of being able to call these functions from an IRQ context.
These new functions race with other contexts, primarily finish_job(),
timedout_job() and recovery(), but I did go through the possible
races between
these(I think). Please let me know what you think of this? I have
not tested
this yet and if this is something in the right direction, I will put
this
through my testing drill and polish it.
IMO I think I prefer the callback approach as it appears to be
simple, less
error prone for both the scheduler and the drivers.
Well I agree that this is way to complicated and looks racy to me as
well. But this is because you moved away from my initial suggestion.
So here is once more how to do it without any additional locks or races:
/**
* drm_sched_suspend_timeout - suspend timeout for reset worker
*
* @sched: scheduler instance for which to suspend the timeout
*
* Suspend the delayed work timeout for the scheduler. Note that
* this function can be called from an IRQ context. It returns the
timeout remaining.
*/
unsigned long drm_sched_suspend_timeout(struct drm_gpu_scheduler *sched)
{
unsigned long timeout, current = jiffies
timeout = sched->work_tdr.timer.expires;
/*
* Set timeout to an arbitrarily large value, this also prevents
the timer to be
* started when new submissions arrive.
*/
if (mod_delayed_work(system_wq, &sched->work_tdr, sched->timeout
* 10) &&
time_after(timeout, current))
return timeout - current;
else
return sched->timeout;
}
/**
* drm_sched_resume_timeout - resume timeout for reset worker
*
* @sched: scheduler instance for which to resume the timeout
* @remaining: remaining timeout
*
* Resume the delayed work timeout for the scheduler. Note that
* this function can be called from an IRQ context.
*/
void drm_sched_resume_timeout(struct drm_gpu_scheduler *sched,
unsigned long remaining)
{
if (list_empty(&sched->ring_mirror_list))
cancel_delayed_work(&sched->work_tdr);
else
mod_delayed_work(system_wq, &sched->work_tdr, remaining);
}
Hi Christian,
Thank you for the suggestions - I was able to try this out this week.
It works for the most part, but there are a couple of races which need
further considerations.
1) The drm_sched_resume_timeout() can race with both the
drm_sched_job_finish() and also new job submissions. In the driver the
job submission which triggered the preemption can be complete as soon
as the switch happens and it is quite possible that I get the
preemption complete and the job done interrupt at the same time. So
this means that drm_sched_resume_timeout() in IRQ context can race
with drm_sched_job_finish() in worker thread context on another CPU.
Also in parallel new jobs can be submitted, which will also update the
ring mirror list . These races can be addressed however with locking
the job_list_lock inside the drm_sched_resume_timeout().
Yeah I know, but I considered this race harmless. Ok, thinking more
about that I realized that this probably means that we could timeout a
job way to early.
How about canceling the timer first and then using mod_delayed_work to
set it to the remaining jiffies if there is a job running?
Do you mean something like this?
void drm_sched_resume_timeout(struct drm_gpu_scheduler *sched,
unsigned long remaining)
{
cancel_delayed_work(&sched->work_tdr);
if (!list_empty(&sched->ring_mirror_list))
mod_delayed_work(system_wq, &sched->work_tdr, remaining);
}
I think that the above can still be racy and I'd prefer locking with the
job_list_lock...
Otherwise as you noted as well the alternative is really to make the
job_list_lock irq safe.
2) This one is a little more tricky - In the driver I start off with
all the timeouts suspended(except the one for the default ring), then
on every preemption interrupt I suspend the outgoing ring and resume
the incoming ring. I can only resume if it was previously suspended.
This is how it is set up. The problem that becomes apparent with this
approach is that for the suspended rings this arbitrarily large
timeout can fire at some point(because of no work) and just before
drm_sched_timedout_job() runs a new job can be inserted into the
mirror list. So in this case we get an incorrect timeout.
What are your thoughts on using cancel_delayed_work() instead of mod
in suspend_timeout. Yes we will lose the benefits of mod, but we
should be able to synchronize drm_sched_suspend_timeout() and
drm_sched_start_timeout() with some basic state. I have not thought
this completely through so I may be missing something here.
Sounds simply like your arbitrary large timeout is not large enough or
do I miss the problem here?
I just suggested regular timeout*10 because at least on our hardware we
still want to have some timeout even if the ring is preempted, but you
could also use MAX_SCHEDULE_TIMEOUT as well.
Okay, yeah using MAX_SCHEDULE_TIMEOUT is a good idea.
I think I will converge on this by adding the job_list_lock to resume
and using MAX_SCHEDULE_TIMEOUT for mod_delayed_work() in
drm_sched_suspend_timeout(). I will try this out.
Sharat
Christian.
Please share your thoughts on this
Thank you
Sharat
Regards,
Christian.
[1] https://patchwork.freedesktop.org/patch/259914/
Signed-off-by: Sharat Masetty <smasetty@xxxxxxxxxxxxxx>
---
drivers/gpu/drm/scheduler/sched_main.c | 81
+++++++++++++++++++++++++++++++++-
include/drm/gpu_scheduler.h | 5 +++
2 files changed, 85 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/scheduler/sched_main.c
b/drivers/gpu/drm/scheduler/sched_main.c
index c993d10..9645789 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -191,11 +191,84 @@ bool drm_sched_dependency_optimized(struct
dma_fence* fence,
*/
static void drm_sched_start_timeout(struct drm_gpu_scheduler *sched)
{
+ unsigned long flags;
+
+ spin_lock_irqsave(&sched->tdr_suspend_lock, flags);
+
+ sched->timeout_remaining = sched->timeout;
+
if (sched->timeout != MAX_SCHEDULE_TIMEOUT &&
- !list_empty(&sched->ring_mirror_list))
+ !list_empty(&sched->ring_mirror_list) &&
!sched->work_tdr_suspended)
schedule_delayed_work(&sched->work_tdr, sched->timeout);
+
+ spin_unlock_irqrestore(&sched->tdr_suspend_lock, flags);
}
+/**
+ * drm_sched_suspend_timeout - suspend timeout for reset worker
+ *
+ * @sched: scheduler instance for which to suspend the timeout
+ *
+ * Suspend the delayed work timeout for the scheduler. Note that
+ * this function can be called from an IRQ context.
+ */
+void drm_sched_suspend_timeout(struct drm_gpu_scheduler *sched)
+{
+ unsigned long flags, timeout;
+
+ spin_lock_irqsave(&sched->tdr_suspend_lock, flags);
+
+ if (sched->work_tdr_suspended ||
+ sched->timeout == MAX_SCHEDULE_TIMEOUT ||
+ list_empty(&sched->ring_mirror_list))
+ goto done;
+
+ timeout = sched->work_tdr.timer.expires;
+
+ /*
+ * Reset timeout to an arbitrarily large value
+ */
+ mod_delayed_work(system_wq, &sched->work_tdr, sched->timeout *
10);
+
+ timeout -= jiffies;
+
+ /* FIXME: Can jiffies be after timeout? */
+ sched->timeout_remaining = time_after(jiffies, timeout)? 0:
timeout;
+ sched->work_tdr_suspended = true;
+
+done:
+ spin_unlock_irqrestore(&sched->tdr_suspend_lock, flags);
+}
+EXPORT_SYMBOL(drm_sched_suspend_timeout);
+
+/**
+ * drm_sched_resume_timeout - resume timeout for reset worker
+ *
+ * @sched: scheduler instance for which to resume the timeout
+ *
+ * Resume the delayed work timeout for the scheduler. Note that
+ * this function can be called from an IRQ context.
+ */
+void drm_sched_resume_timeout(struct drm_gpu_scheduler *sched)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&sched->tdr_suspend_lock, flags);
+
+ if (!sched->work_tdr_suspended ||
+ sched->timeout == MAX_SCHEDULE_TIMEOUT) {
+ spin_unlock_irqrestore(&sched->tdr_suspend_lock, flags);
+ return;
+ }
+
+ mod_delayed_work(system_wq, &sched->work_tdr,
sched->timeout_remaining);
+
+ sched->work_tdr_suspended = false;
+
+ spin_unlock_irqrestore(&sched->tdr_suspend_lock, flags);
+}
+EXPORT_SYMBOL(drm_sched_resume_timeout);
+
/* job_finish is called after hw fence signaled
*/
static void drm_sched_job_finish(struct work_struct *work)
@@ -348,6 +421,11 @@ void drm_sched_job_recovery(struct
drm_gpu_scheduler *sched)
struct drm_sched_job *s_job, *tmp;
bool found_guilty = false;
int r;
+ unsigned long flags;
+
+ spin_lock_irqsave(&sched->tdr_suspend_lock, flags);
+ sched->work_tdr_suspended = false;
+ spin_unlock_irqrestore(&sched->tdr_suspend_lock, flags);
spin_lock(&sched->job_list_lock);
list_for_each_entry_safe(s_job, tmp,
&sched->ring_mirror_list, node) {
@@ -607,6 +685,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
init_waitqueue_head(&sched->job_scheduled);
INIT_LIST_HEAD(&sched->ring_mirror_list);
spin_lock_init(&sched->job_list_lock);
+ spin_lock_init(&sched->tdr_suspend_lock);
atomic_set(&sched->hw_rq_count, 0);
INIT_DELAYED_WORK(&sched->work_tdr, drm_sched_job_timedout);
atomic_set(&sched->num_jobs, 0);
diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index d87b268..5d39572 100644
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -278,6 +278,9 @@ struct drm_gpu_scheduler {
atomic_t hw_rq_count;
atomic64_t job_id_count;
struct delayed_work work_tdr;
+ unsigned long timeout_remaining;
+ bool work_tdr_suspended;
+ spinlock_t tdr_suspend_lock;
struct task_struct *thread;
struct list_head ring_mirror_list;
spinlock_t job_list_lock;
@@ -300,6 +303,8 @@ void drm_sched_hw_job_reset(struct
drm_gpu_scheduler *sched,
bool drm_sched_dependency_optimized(struct dma_fence* fence,
struct drm_sched_entity *entity);
void drm_sched_job_kickout(struct drm_sched_job *s_job);
+void drm_sched_suspend_timeout(struct drm_gpu_scheduler *sched);
+void drm_sched_resume_timeout(struct drm_gpu_scheduler *sched);
void drm_sched_rq_add_entity(struct drm_sched_rq *rq,
struct drm_sched_entity *entity);
--
1.9.1
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