On 2021-04-15 3:02 a.m., Christian König wrote:
Am 15.04.21 um 08:27 schrieb Andrey Grodzovsky:
On 2021-04-14 10:58 a.m., Christian König wrote:
Am 14.04.21 um 16:36 schrieb Andrey Grodzovsky:
[SNIP]
We are racing here once more and need to handle that.
But why, I wrote above that we first stop the all schedulers,
then only call drm_sched_entity_kill_jobs.
The schedulers consuming jobs is not the problem, we already
handle that correct.
The problem is that the entities might continue feeding stuff into
the scheduler.
Missed that. Ok, can I just use non sleeping RCU with a flag
around drm_sched_entity_push_job at the amdgpu level (only 2
functions call it - amdgpu_cs_submit and amdgpu_job_submit) as a
preliminary step to flush and block in flight and future
submissions to entity queue ?
Double checking the code I think we can use the notifier_lock for this.
E.g. in amdgpu_cs.c see where we have the goto error_abort.
That is the place where such a check could be added without any
additional overhead.
Sure, I will just have to add this lock to amdgpu_job_submit too.
Not ideal, but I think that's fine with me. You might want to rename
the lock for this thought.
[SNIP]
Maybe just empirically - let's try it and see under different
test scenarios what actually happens ?
Not a good idea in general, we have that approach way to often at
AMD and are then surprised that everything works in QA but fails
in production.
But Daniel already noted in his reply that waiting for a fence
while holding the SRCU is expected to work.
So let's stick with the approach of high level locking for hotplug.
To my understanding this is true for other devises, not the one
being extracted, for him you still need to do all the HW fence
signalling dance because the HW is gone and we block any TDRs
(which won't help anyway).
Andrey
Do you agree to the above ?
Yeah, I think that is correct.
But on the other hand what Daniel reminded me of is that the handling
needs to be consistent over different devices. And since some device
already go with the approach of canceling everything we simply have to
go down that route as well.
Christian.
What does it mean in our context ? What needs to be done which we are
not doing now ?
Andrey
Andrey
Christian.
Andrey
Christian.
Andrey
Regards,
Christian.
Andrey
BTW: Could it be that the device SRCU protects more than
one device and we deadlock because of this?
I haven't actually experienced any deadlock until now
but, yes, drm_unplug_srcu is defined as static in
drm_drv.c and so in the presence of multiple devices from
same or different drivers we in fact are dependent on all
their critical sections i guess.
Shit, yeah the devil is a squirrel. So for A+I laptops we
actually need to sync that up with Daniel and the rest of
the i915 guys.
IIRC we could actually have an amdgpu device in a docking
station which needs hotplug and the driver might depend on
waiting for the i915 driver as well.
Can't we propose a patch to make drm_unplug_srcu per
drm_device ? I don't see why it has to be global and not
per device thing.
I'm really wondering the same thing for quite a while now.
Adding Daniel as well, maybe he knows why the
drm_unplug_srcu is global.
Regards,
Christian.
Andrey
Christian.
Andrey
Christian.
Andrey
Andrey
Christian.
/* Past this point no more fence are submitted
to HW ring and hence we can safely call force
signal on all that are currently there.
* Any subsequently created HW fences will be
returned signaled with an error code right away
*/
for_each_ring(adev)
amdgpu_fence_process(ring)
drm_dev_unplug(dev);
Stop schedulers
cancel_sync(all timers and queued works);
hw_fini
unmap_mmio
}
Andrey
Alternatively grabbing the reset write side
and stopping and then restarting the scheduler
could work as well.
Christian.
I didn't get the above and I don't see why I
need to reuse the GPU reset rw_lock. I rely on
the SRCU unplug flag for unplug. Also, not
clear to me why are we focusing on the
scheduler threads, any code patch to generate
HW fences should be covered, so any code
leading to amdgpu_fence_emit needs to be taken
into account such as, direct IB submissions, VM
flushes e.t.c
You need to work together with the reset lock
anyway, cause a hotplug could run at the same
time as a reset.
For going my way indeed now I see now that I have
to take reset write side lock during HW fences
signalling in order to protect against
scheduler/HW fences detachment and reattachment
during schedulers stop/restart. But if we go with
your approach then calling drm_dev_unplug and
scoping amdgpu_job_timeout with
drm_dev_enter/exit should be enough to prevent
any concurrent GPU resets during unplug. In fact
I already do it anyway -
https://nam11.safelinks.protection.outlook.com/?url=https:%2F%2Fcgit.freedesktop.org%2F~agrodzov%2Flinux%2Fcommit%2F%3Fh%3Ddrm-misc-next%26id%3Def0ea4dd29ef44d2649c5eda16c8f4869acc36b1&data=04%7C01%7Candrey.grodzovsky%40amd.com%7Ca64b1f5e0df0403a656408d8ffdc7bdb%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637540669732692484%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=pLcplnlDIESV998tLO7iydxEo5lh71BjQCbAOxKif2Q%3D&reserved=0
Yes, good point as well.
Christian.
Andrey
Christian.
Andrey
Christian.
Andrey
Andrey
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