On 2021-11-10 8:24 a.m., Daniel Vetter wrote:
On Wed, Nov 10, 2021 at 11:09:50AM +0100, Christian König wrote:
Am 10.11.21 um 10:50 schrieb Daniel Vetter:
On Tue, Nov 09, 2021 at 08:17:01AM -0800, Rob Clark wrote:
On Tue, Nov 9, 2021 at 1:07 AM Daniel Vetter <daniel@xxxxxxxx> wrote:
On Mon, Nov 08, 2021 at 03:39:17PM -0800, Rob Clark wrote:
I stumbled across this thread when I ran into the same issue, while
working out how to move drm/msm to use scheduler's retire +
timeout/recovery (and get rid of our own mirror list of in-flight
jobs). We already have hw error detection enabled, and it can signal
quite fast, so assuming the first job on the list is the guilty job
just won't work.
But I was considering a slightly different approach to fixing this,
instead just handling it all in drm_sched_main() and getting rid of
the complicated kthread parking gymnastics. Ie. something along the
lines of:
So handling timeouts in the main sched thread wont work as soon as you
have multiple engines and reset that impacts across engines:
- Nothing is simplified since you still need to stop the other scheduler
threads.
- You get deadlocks if 2 schedulers time out at the same time, and both
want to stop the other one.
Hence workqueue. Now the rule for the wq is that you can only have one per
reset domain, so
- single engine you just take the one drm/sched provides
- if reset affects all your engines in the chip, then you allocate on in
the drm_device and pass that to all
- if you have a complex of gpus all interconnected (e.g. xgmi hive for
amd), then it's one wq for the entire hive
_All_ reset related things must be run on that workqueue or things breaks,
which means if you get hw fault that also needs to be run there. I guess
we should either patch drm/sched to check you call that function from the
right workqueue, or just handle it internally.
Hmm, ok.. I guess it would be useful to better document the reasoning
for the current design, that would have steered me more towards the
approach taken in this patch.
Maybe this was because you worked on an old kernel? Boris did update the
kerneldoc as part of making gpu reset work for panfrost, which has this
multi-engine reset problem. If that's not yet clear then we need to
improve the docs further.
AMD's problem is even worse, because their reset domain is the entire xgmi
hive, so multiple pci devices.
I'm pushing for quite a while that we get something like an
amdgpu_reset_domain structure or similar for this, but we unfortunately
don't have that yet.
Maybe it should be a good idea to have something like a drm_sched_domain or
similar with all the necessary information for the inter scheduler handling.
E.g. a workqueue for reset etc...
Yeah I think as soon as we have more stuff than just the wq then a
drm_sched_reset_domain sounds good.
But if it's just driver stuff (e.g. the xgmi locking you have in amdgpu
reset comes to mind) then I think just a driver_reset_domain struct that
bundles all that stuff up seems good enough.
E.g. on i915 I'm also pondering whether some of the fw requests should be
processed by the reset wq, to avoid locking headaches, so I don't think
hiding that work too much in abstractions is a good idea.
-Daniel
I suggest we keep the drm_sched_reset_domain as a base struct to hold the wq
(and possible something else cross drivers in the future) and then embed
it in a derived
driver specific struct to hold driver specific stuff like
the XGMI lock you mentioned.
Andrey
Regards,
Christian.
Also there might more issues in drm/sched ofc, e.g. I've looked a bit at
ordering/barriers and I'm pretty sure a lot are still missing. Or at least
we should have comments in the code explaining why it all works.
-Daniel
BR,
-R
-Daniel
---------------------
diff --git a/drivers/gpu/drm/scheduler/sched_main.c
b/drivers/gpu/drm/scheduler/sched_main.c
index 67382621b429..4d6ce775c316 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -764,6 +764,45 @@ static bool drm_sched_blocked(struct
drm_gpu_scheduler *sched)
return false;
}
+static bool handle_timeout(struct drm_gpu_scheduler *sched)
+{
+ struct drm_sched_job *bad;
+
+ if (!sched->has_timeout)
+ return false;
+
+ sched->has_timeout = false;
+
+ spin_lock(&sched->job_list_lock);
+ bad = list_first_entry_or_null(&sched->pending_list,
+ struct drm_sched_job, list);
+
+ if (!bad) {
+ spin_unlock(&sched->job_list_lock);
+ return false;
+ }
+
+ spin_unlock(&sched->job_list_lock);
+
+ if (sched->timeout_wq == system_wq) {
+ /*
+ * If driver has no specific requirements about serializing
+ * reset wrt. other engines, just call timedout_job() directly
+ */
+ sched->ops->timedout_job(job);
+ } else {
+ /*
+ * Otherwise queue it on timeout_wq and wait for it to complete
+ */
+ ... more typing needed here ...
+ }
+
+ if (sched->free_guilty) {
+ sched->ops->free_job(job);
+ sched->free_guilty = false;
+ }
+}
+
/**
* drm_sched_main - main scheduler thread
*
@@ -787,6 +826,7 @@ static int drm_sched_main(void *param)
wait_event_interruptible(sched->wake_up_worker,
(cleanup_job =
drm_sched_get_cleanup_job(sched)) ||
+ handle_timeout(sched) ||
(!drm_sched_blocked(sched) &&
(entity =
drm_sched_select_entity(sched))) ||
kthread_should_stop());
---------------------
drm_sched_fault() and the sw timeout handler would just set
sched->has_timeout and kick sched->wake_up_worker.
And since we handle the timeout case after
drm_sched_get_cleanup_job(), we know that all of the successfully
completed jobs have already been popped off the list, and won't be
unfairly maligned.
BR,
-R
On Tue, Aug 31, 2021 at 6:29 PM Liu, Monk <Monk.Liu@xxxxxxx> wrote:
[AMD Official Use Only]
Okay, I will reprepare this patch
Thanks
------------------------------------------
Monk Liu | Cloud-GPU Core team
------------------------------------------
-----Original Message-----
From: Daniel Vetter <daniel@xxxxxxxx>
Sent: Tuesday, August 31, 2021 9:02 PM
To: Liu, Monk <Monk.Liu@xxxxxxx>
Cc: amd-gfx@xxxxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; Chen, Jingwen <Jingwen.Chen@xxxxxxx>
Subject: Re: [PATCH 2/2] drm/sched: serialize job_timeout and scheduler
On Tue, Aug 31, 2021 at 02:59:02PM +0200, Daniel Vetter wrote:
Can we please have some actual commit message here, with detailed
explanation of the race/bug/whatever, how you fix it and why this is
the best option?
On Tue, Aug 31, 2021 at 06:35:39PM +0800, Monk Liu wrote:
tested-by: jingwen chen <jingwen.chen@xxxxxxx>
Signed-off-by: Monk Liu <Monk.Liu@xxxxxxx>
Signed-off-by: jingwen chen <jingwen.chen@xxxxxxx>
---
drivers/gpu/drm/scheduler/sched_main.c | 24
++++--------------------
1 file changed, 4 insertions(+), 20 deletions(-)
diff --git a/drivers/gpu/drm/scheduler/sched_main.c
b/drivers/gpu/drm/scheduler/sched_main.c
index ecf8140..894fdb24 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -319,19 +319,17 @@ static void drm_sched_job_timedout(struct work_struct *work)
sched = container_of(work, struct drm_gpu_scheduler,
work_tdr.work);
/* Protects against concurrent deletion in
drm_sched_get_cleanup_job */
+ if (!__kthread_should_park(sched->thread))
This is a __ function, i.e. considered internal, and it's lockless
atomic, i.e. unordered. And you're not explaining why this works.
Iow it's probably buggy, and an just unconditionally parking the
kthread is probably the right thing to do. If it's not the right thing
to do, there's a bug here for sure.
Also why don't we reuse the function drivers already have to stop a scheduler thread? We seem to have two kthread_park now, that's probably one too much.
-Daniel
+ kthread_park(sched->thread);
+
spin_lock(&sched->job_list_lock);
job = list_first_entry_or_null(&sched->pending_list,
struct drm_sched_job, list);
if (job) {
- /*
- * Remove the bad job so it cannot be freed by concurrent
- * drm_sched_cleanup_jobs. It will be reinserted back after sched->thread
- * is parked at which point it's safe.
- */
- list_del_init(&job->list);
spin_unlock(&sched->job_list_lock);
+ /* vendor's timeout_job should call drm_sched_start() */
status = job->sched->ops->timedout_job(job);
/*
@@ -393,20 +391,6 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
kthread_park(sched->thread);
/*
- * Reinsert back the bad job here - now it's safe as
- * drm_sched_get_cleanup_job cannot race against us and release the
- * bad job at this point - we parked (waited for) any in progress
- * (earlier) cleanups and drm_sched_get_cleanup_job will not be called
- * now until the scheduler thread is unparked.
- */
- if (bad && bad->sched == sched)
- /*
- * Add at the head of the queue to reflect it was the earliest
- * job extracted.
- */
- list_add(&bad->list, &sched->pending_list);
-
- /*
* Iterate the job list from later to earlier one and either deactive
* their HW callbacks or remove them from pending list if they already
* signaled.
--
2.7.4
--
Daniel Vetter
Software Engineer, Intel Corporation
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Daniel Vetter
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Daniel Vetter
Software Engineer, Intel Corporation
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