Re: Threaded submission & semaphore sharing

[Lionel Landwerlin]

Went through the spec VUs again and there is a bit that says that binary 
semaphores must have all of the their dependencies submitted for execution.
So essentially it means in our implementation of QueueSubmit() we should 
be able to do a short wait_for_available on all of those which does 
ensure everything is properly ordered.


So I think you're right on this David, waitBeforeSignal on binary 
semaphore is out of scope.


Again sorry for the noise.

-Lionel

On 02/08/2019 13:01, zhoucm1 wrote:




On 2019年08月02日 17:41, Lionel Landwerlin wrote:

Hey David,

On 02/08/2019 12:11, zhoucm1 wrote:


Hi Lionel,

For binary semaphore, I guess every one will think application will 
guarantee wait is behind the signal, whenever the semaphore is 
shared or used in internal-process.


I think below two options can fix your problem:

a. Can we extend vkWaitForFence so that it can be able to wait on 
fence-available? If fence is available, then it's safe to do 
semaphore wait in vkQueueSubmit.




I'm sorry, but I don't understand what vkWaitForFence() has to do 
with this problem.


They test case we're struggling with doesn't use that API.


Can you maybe explain a bit more how it relates?


vkQueueSubmit()
vkWaitForFenceAvailable()
vkQueueSubmit()
vkWaitForFenceAvailable()
vkQueueSubmit()
vkWaitForFenceAvailable()

Sorry, that could lead application program very ugly.



b. Make waitBeforeSignal is valid for binary semaphore as well, as 
that way, It is reasonable to add wait/signal counting for binary 
syncobj.




Yeah essentially the change we're proposing internally makes binary 
semaphores use syncobj timelines.


Will you raise up a MR to add the language of waitBeforeSignal support 
of binary semaphore to vulkan spec?


-David


There is just another u64 associated with them.


-Lionel




-David


On 2019年08月02日 14:27, Lionel Landwerlin wrote:

On 02/08/2019 09:10, Koenig, Christian wrote:



Am 02.08.2019 07:38 schrieb Lionel Landwerlin 
:


On 02/08/2019 08:21, Koenig, Christian wrote:



Am 02.08.2019 07:17 schrieb Lionel Landwerlin

:

On 02/08/2019 08:08, Koenig, Christian wrote:

Hi Lionel,

Well that looks more like your test case is buggy.

According to the code the ctx1 queue always waits
for sem1 and ctx2 queue always waits for sem2.


That's supposed to be the same underlying syncobj
because it's exported from one VkDevice as opaque FD
from sem1 and imported into sem2.


Well than that's still buggy and won't synchronize at all.

When ctx1 waits for a semaphore and then signals the same
semaphore there is no guarantee that ctx2 will run in
between jobs.

It's perfectly valid in this case to first run all jobs
from ctx1 and then all jobs from ctx2.


That's not really how I see the semaphores working.

The spec describe VkSemaphore as an interface to an internal
payload opaque to the application.


When ctx1 waits on the semaphore, it waits on the payload put
there by the previous iteration.


And who says that it's not waiting for it's own previous payload?



That's was I understood from you previous comment : "there is no 
guarantee that ctx2 will run in between jobs"





See if the payload is a counter this won't work either. Keep in 
mind that this has the semantic of a semaphore. Whoever grabs the 
semaphore first wins and can run, everybody else has to wait.



What performs the "grab" here?

I thought that would be vkQueueSubmit().

Since that occuring from a single application thread, that should 
then be ordered in execution of ctx1,ctx2,ctx1,...



Thanks for your time on this,


-Lionel




Then it proceeds to signal it by replacing the internal payload.


That's an implementation detail of our sync objects, but I don't 
think that this behavior is part of the Vulkan specification.


Regards,
Christian.


ctx2 then waits on that and replaces the payload again with
the new internal synchronization object.


The internal payload is a dma fence in our case and signaling
just replaces a dma fence by another or puts one where there
was none before.

So we should have created a dependecy link between all the
submissions and then should be executed in the order of
QueueSubmit() calls.


-Lionel



It only prevents running both at the same time and as far
as I can see that still works even with threaded submission.

You need at least two semaphores for a tandem submission.

Regards,
Christian.



This way there can't be any Synchronisation
between the two.

Regards,
Christian.

Am 02.08.2019 06:55 schrieb Lionel Landwerlin

Re: Threaded submission & semaphore sharing

[zhoucm1]

On 2019年08月02日 17:41, Lionel Landwerlin wrote:

Hey David,

On 02/08/2019 12:11, zhoucm1 wrote:


Hi Lionel,

For binary semaphore, I guess every one will think application will 
guarantee wait is behind the signal, whenever the semaphore is shared 
or used in internal-process.


I think below two options can fix your problem:

a. Can we extend vkWaitForFence so that it can be able to wait on 
fence-available? If fence is available, then it's safe to do 
semaphore wait in vkQueueSubmit.




I'm sorry, but I don't understand what vkWaitForFence() has to do with 
this problem.


They test case we're struggling with doesn't use that API.


Can you maybe explain a bit more how it relates?


vkQueueSubmit()
vkWaitForFenceAvailable()
vkQueueSubmit()
vkWaitForFenceAvailable()
vkQueueSubmit()
vkWaitForFenceAvailable()

Sorry, that could lead application program very ugly.



b. Make waitBeforeSignal is valid for binary semaphore as well, as 
that way, It is reasonable to add wait/signal counting for binary 
syncobj.




Yeah essentially the change we're proposing internally makes binary 
semaphores use syncobj timelines.


Will you raise up a MR to add the language of waitBeforeSignal support 
of binary semaphore to vulkan spec?


-David


There is just another u64 associated with them.


-Lionel




-David


On 2019年08月02日 14:27, Lionel Landwerlin wrote:

On 02/08/2019 09:10, Koenig, Christian wrote:



Am 02.08.2019 07:38 schrieb Lionel Landwerlin 
:


On 02/08/2019 08:21, Koenig, Christian wrote:



Am 02.08.2019 07:17 schrieb Lionel Landwerlin

:

On 02/08/2019 08:08, Koenig, Christian wrote:

Hi Lionel,

Well that looks more like your test case is buggy.

According to the code the ctx1 queue always waits
for sem1 and ctx2 queue always waits for sem2.


That's supposed to be the same underlying syncobj
because it's exported from one VkDevice as opaque FD
from sem1 and imported into sem2.


Well than that's still buggy and won't synchronize at all.

When ctx1 waits for a semaphore and then signals the same
semaphore there is no guarantee that ctx2 will run in
between jobs.

It's perfectly valid in this case to first run all jobs
from ctx1 and then all jobs from ctx2.


That's not really how I see the semaphores working.

The spec describe VkSemaphore as an interface to an internal
payload opaque to the application.


When ctx1 waits on the semaphore, it waits on the payload put
there by the previous iteration.


And who says that it's not waiting for it's own previous payload?



That's was I understood from you previous comment : "there is no 
guarantee that ctx2 will run in between jobs"





See if the payload is a counter this won't work either. Keep in 
mind that this has the semantic of a semaphore. Whoever grabs the 
semaphore first wins and can run, everybody else has to wait.



What performs the "grab" here?

I thought that would be vkQueueSubmit().

Since that occuring from a single application thread, that should 
then be ordered in execution of ctx1,ctx2,ctx1,...



Thanks for your time on this,


-Lionel




Then it proceeds to signal it by replacing the internal payload.


That's an implementation detail of our sync objects, but I don't 
think that this behavior is part of the Vulkan specification.


Regards,
Christian.


ctx2 then waits on that and replaces the payload again with the
new internal synchronization object.


The internal payload is a dma fence in our case and signaling
just replaces a dma fence by another or puts one where there
was none before.

So we should have created a dependecy link between all the
submissions and then should be executed in the order of
QueueSubmit() calls.


-Lionel



It only prevents running both at the same time and as far
as I can see that still works even with threaded submission.

You need at least two semaphores for a tandem submission.

Regards,
Christian.



This way there can't be any Synchronisation between
the two.

Regards,
Christian.

Am 02.08.2019 06:55 schrieb Lionel Landwerlin

:
Hey Christian,

The problem boils down to the fact that we don't
immediately create dma fences when calling
vkQueueSubmit().
This is delayed to a thread.

From a single application thread, you can
QueueSubmit() to 2 queues from 2 different devices.
Each QueueSubmit to one queue has a dependency on
the previous QueueSubmit on the other queue through
  

Re: Threaded submission & semaphore sharing

[Lionel Landwerlin]

Hey David,

On 02/08/2019 12:11, zhoucm1 wrote:


Hi Lionel,

For binary semaphore, I guess every one will think application will 
guarantee wait is behind the signal, whenever the semaphore is shared 
or used in internal-process.


I think below two options can fix your problem:

a. Can we extend vkWaitForFence so that it can be able to wait on 
fence-available? If fence is available, then it's safe to do semaphore 
wait in vkQueueSubmit.




I'm sorry, but I don't understand what vkWaitForFence() has to do with 
this problem.


They test case we're struggling with doesn't use that API.


Can you maybe explain a bit more how it relates?


b. Make waitBeforeSignal is valid for binary semaphore as well, as 
that way, It is reasonable to add wait/signal counting for binary syncobj.




Yeah essentially the change we're proposing internally makes binary 
semaphores use syncobj timelines.


There is just another u64 associated with them.


-Lionel




-David


On 2019年08月02日 14:27, Lionel Landwerlin wrote:

On 02/08/2019 09:10, Koenig, Christian wrote:



Am 02.08.2019 07:38 schrieb Lionel Landwerlin 
:


On 02/08/2019 08:21, Koenig, Christian wrote:



Am 02.08.2019 07:17 schrieb Lionel Landwerlin

:

On 02/08/2019 08:08, Koenig, Christian wrote:

Hi Lionel,

Well that looks more like your test case is buggy.

According to the code the ctx1 queue always waits
for sem1 and ctx2 queue always waits for sem2.


That's supposed to be the same underlying syncobj
because it's exported from one VkDevice as opaque FD
from sem1 and imported into sem2.


Well than that's still buggy and won't synchronize at all.

When ctx1 waits for a semaphore and then signals the same
semaphore there is no guarantee that ctx2 will run in
between jobs.

It's perfectly valid in this case to first run all jobs from
ctx1 and then all jobs from ctx2.


That's not really how I see the semaphores working.

The spec describe VkSemaphore as an interface to an internal
payload opaque to the application.


When ctx1 waits on the semaphore, it waits on the payload put
there by the previous iteration.


And who says that it's not waiting for it's own previous payload?



That's was I understood from you previous comment : "there is no 
guarantee that ctx2 will run in between jobs"





See if the payload is a counter this won't work either. Keep in mind 
that this has the semantic of a semaphore. Whoever grabs the 
semaphore first wins and can run, everybody else has to wait.



What performs the "grab" here?

I thought that would be vkQueueSubmit().

Since that occuring from a single application thread, that should 
then be ordered in execution of ctx1,ctx2,ctx1,...



Thanks for your time on this,


-Lionel




Then it proceeds to signal it by replacing the internal payload.


That's an implementation detail of our sync objects, but I don't 
think that this behavior is part of the Vulkan specification.


Regards,
Christian.


ctx2 then waits on that and replaces the payload again with the
new internal synchronization object.


The internal payload is a dma fence in our case and signaling
just replaces a dma fence by another or puts one where there was
none before.

So we should have created a dependecy link between all the
submissions and then should be executed in the order of
QueueSubmit() calls.


-Lionel



It only prevents running both at the same time and as far as
I can see that still works even with threaded submission.

You need at least two semaphores for a tandem submission.

Regards,
Christian.



This way there can't be any Synchronisation between
the two.

Regards,
Christian.

Am 02.08.2019 06:55 schrieb Lionel Landwerlin

:
Hey Christian,

The problem boils down to the fact that we don't
immediately create dma fences when calling
vkQueueSubmit().
This is delayed to a thread.

From a single application thread, you can
QueueSubmit() to 2 queues from 2 different devices.
Each QueueSubmit to one queue has a dependency on
the previous QueueSubmit on the other queue through
an exported/imported semaphore.

From the API point of view the state of the
semaphore should be changed after each QueueSubmit().
The problem is that it's not because of the thread
and because you might have those 2 submission
threads tied to different 

Re: Threaded submission & semaphore sharing

[zhoucm1]

Hi Lionel,

For binary semaphore, I guess every one will think application will 
guarantee wait is behind the signal, whenever the semaphore is shared or 
used in internal-process.


I think below two options can fix your problem:

a. Can we extend vkWaitForFence so that it can be able to wait on 
fence-available? If fence is available, then it's safe to do semaphore 
wait in vkQueueSubmit.


b. Make waitBeforeSignal is valid for binary semaphore as well, as that 
way, It is reasonable to add wait/signal counting for binary syncobj.



-David


On 2019年08月02日 14:27, Lionel Landwerlin wrote:

On 02/08/2019 09:10, Koenig, Christian wrote:



Am 02.08.2019 07:38 schrieb Lionel Landwerlin 
:


On 02/08/2019 08:21, Koenig, Christian wrote:



Am 02.08.2019 07:17 schrieb Lionel Landwerlin

:

On 02/08/2019 08:08, Koenig, Christian wrote:

Hi Lionel,

Well that looks more like your test case is buggy.

According to the code the ctx1 queue always waits for
sem1 and ctx2 queue always waits for sem2.


That's supposed to be the same underlying syncobj because
it's exported from one VkDevice as opaque FD from sem1
and imported into sem2.


Well than that's still buggy and won't synchronize at all.

When ctx1 waits for a semaphore and then signals the same
semaphore there is no guarantee that ctx2 will run in between
jobs.

It's perfectly valid in this case to first run all jobs from
ctx1 and then all jobs from ctx2.


That's not really how I see the semaphores working.

The spec describe VkSemaphore as an interface to an internal
payload opaque to the application.


When ctx1 waits on the semaphore, it waits on the payload put
there by the previous iteration.


And who says that it's not waiting for it's own previous payload?



That's was I understood from you previous comment : "there is no 
guarantee that ctx2 will run in between jobs"





See if the payload is a counter this won't work either. Keep in mind 
that this has the semantic of a semaphore. Whoever grabs the 
semaphore first wins and can run, everybody else has to wait.



What performs the "grab" here?

I thought that would be vkQueueSubmit().

Since that occuring from a single application thread, that should then 
be ordered in execution of ctx1,ctx2,ctx1,...



Thanks for your time on this,


-Lionel




Then it proceeds to signal it by replacing the internal payload.


That's an implementation detail of our sync objects, but I don't 
think that this behavior is part of the Vulkan specification.


Regards,
Christian.


ctx2 then waits on that and replaces the payload again with the
new internal synchronization object.


The internal payload is a dma fence in our case and signaling
just replaces a dma fence by another or puts one where there was
none before.

So we should have created a dependecy link between all the
submissions and then should be executed in the order of
QueueSubmit() calls.


-Lionel



It only prevents running both at the same time and as far as
I can see that still works even with threaded submission.

You need at least two semaphores for a tandem submission.

Regards,
Christian.



This way there can't be any Synchronisation between
the two.

Regards,
Christian.

Am 02.08.2019 06:55 schrieb Lionel Landwerlin

:
Hey Christian,

The problem boils down to the fact that we don't
immediately create dma fences when calling
vkQueueSubmit().
This is delayed to a thread.

From a single application thread, you can
QueueSubmit() to 2 queues from 2 different devices.
Each QueueSubmit to one queue has a dependency on the
previous QueueSubmit on the other queue through an
exported/imported semaphore.

From the API point of view the state of the semaphore
should be changed after each QueueSubmit().
The problem is that it's not because of the thread
and because you might have those 2 submission threads
tied to different VkDevice/VkInstance or even
different applications (synchronizing themselves
outside the vulkan API).

Hope that makes sense.
It's not really easy to explain by mail, the best
explanation is probably reading the test :

https://gitlab.freedesktop.org/mesa/crucible/blob/master/src/tests/func/sync/semaphore-fd.c#L788

Re: Threaded submission & semaphore sharing

[Lionel Landwerlin]

On 02/08/2019 09:10, Koenig, Christian wrote:



Am 02.08.2019 07:38 schrieb Lionel Landwerlin 
:


On 02/08/2019 08:21, Koenig, Christian wrote:



Am 02.08.2019 07:17 schrieb Lionel Landwerlin

:

On 02/08/2019 08:08, Koenig, Christian wrote:

Hi Lionel,

Well that looks more like your test case is buggy.

According to the code the ctx1 queue always waits for
sem1 and ctx2 queue always waits for sem2.


That's supposed to be the same underlying syncobj because
it's exported from one VkDevice as opaque FD from sem1 and
imported into sem2.


Well than that's still buggy and won't synchronize at all.

When ctx1 waits for a semaphore and then signals the same
semaphore there is no guarantee that ctx2 will run in between
jobs.

It's perfectly valid in this case to first run all jobs from
ctx1 and then all jobs from ctx2.


That's not really how I see the semaphores working.

The spec describe VkSemaphore as an interface to an internal
payload opaque to the application.


When ctx1 waits on the semaphore, it waits on the payload put
there by the previous iteration.


And who says that it's not waiting for it's own previous payload?



That's was I understood from you previous comment : "there is no 
guarantee that ctx2 will run in between jobs"





See if the payload is a counter this won't work either. Keep in mind 
that this has the semantic of a semaphore. Whoever grabs the semaphore 
first wins and can run, everybody else has to wait.



What performs the "grab" here?

I thought that would be vkQueueSubmit().

Since that occuring from a single application thread, that should then 
be ordered in execution of ctx1,ctx2,ctx1,...



Thanks for your time on this,


-Lionel




Then it proceeds to signal it by replacing the internal payload.


That's an implementation detail of our sync objects, but I don't think 
that this behavior is part of the Vulkan specification.


Regards,
Christian.


ctx2 then waits on that and replaces the payload again with the
new internal synchronization object.


The internal payload is a dma fence in our case and signaling just
replaces a dma fence by another or puts one where there was none
before.

So we should have created a dependecy link between all the
submissions and then should be executed in the order of
QueueSubmit() calls.


-Lionel



It only prevents running both at the same time and as far as I
can see that still works even with threaded submission.

You need at least two semaphores for a tandem submission.

Regards,
Christian.



This way there can't be any Synchronisation between
the two.

Regards,
Christian.

Am 02.08.2019 06:55 schrieb Lionel Landwerlin

:
Hey Christian,

The problem boils down to the fact that we don't
immediately create dma fences when calling
vkQueueSubmit().
This is delayed to a thread.

From a single application thread, you can
QueueSubmit() to 2 queues from 2 different devices.
Each QueueSubmit to one queue has a dependency on the
previous QueueSubmit on the other queue through an
exported/imported semaphore.

From the API point of view the state of the semaphore
should be changed after each QueueSubmit().
The problem is that it's not because of the thread and
because you might have those 2 submission threads tied
to different VkDevice/VkInstance or even different
applications (synchronizing themselves outside the
vulkan API).

Hope that makes sense.
It's not really easy to explain by mail, the best
explanation is probably reading the test :

https://gitlab.freedesktop.org/mesa/crucible/blob/master/src/tests/func/sync/semaphore-fd.c#L788

Like David mentioned you're not running into that
issue right now, because you only dispatch to the
thread under specific conditions.
But I could build a case to force that and likely run
into the same issue.

-Lionel

On 02/08/2019 07:33, Koenig, Christian wrote:

Hi Lionel,

Well could you describe once more what the problem is?

Cause I don't fully understand why a rather normal
tandem submission with two semaphores 

Re: Threaded submission & semaphore sharing

[Koenig, Christian]

Am 02.08.2019 07:38 schrieb Lionel Landwerlin :
On 02/08/2019 08:21, Koenig, Christian wrote:


Am 02.08.2019 07:17 schrieb Lionel Landwerlin 
:
On 02/08/2019 08:08, Koenig, Christian wrote:
Hi Lionel,

Well that looks more like your test case is buggy.

According to the code the ctx1 queue always waits for sem1 and ctx2 queue 
always waits for sem2.


That's supposed to be the same underlying syncobj because it's exported from 
one VkDevice as opaque FD from sem1 and imported into sem2.

Well than that's still buggy and won't synchronize at all.

When ctx1 waits for a semaphore and then signals the same semaphore there is no 
guarantee that ctx2 will run in between jobs.

It's perfectly valid in this case to first run all jobs from ctx1 and then all 
jobs from ctx2.


That's not really how I see the semaphores working.

The spec describe VkSemaphore as an interface to an internal payload opaque to 
the application.


When ctx1 waits on the semaphore, it waits on the payload put there by the 
previous iteration.

And who says that it's not waiting for it's own previous payload?

See if the payload is a counter this won't work either. Keep in mind that this 
has the semantic of a semaphore. Whoever grabs the semaphore first wins and can 
run, everybody else has to wait.


Then it proceeds to signal it by replacing the internal payload.

That's an implementation detail of our sync objects, but I don't think that 
this behavior is part of the Vulkan specification.

Regards,
Christian.


ctx2 then waits on that and replaces the payload again with the new internal 
synchronization object.


The internal payload is a dma fence in our case and signaling just replaces a 
dma fence by another or puts one where there was none before.

So we should have created a dependecy link between all the submissions and then 
should be executed in the order of QueueSubmit() calls.


-Lionel


It only prevents running both at the same time and as far as I can see that 
still works even with threaded submission.

You need at least two semaphores for a tandem submission.

Regards,
Christian.


This way there can't be any Synchronisation between the two.

Regards,
Christian.

Am 02.08.2019 06:55 schrieb Lionel Landwerlin 
:
Hey Christian,

The problem boils down to the fact that we don't immediately create dma fences 
when calling vkQueueSubmit().
This is delayed to a thread.

From a single application thread, you can QueueSubmit() to 2 queues from 2 
different devices.
Each QueueSubmit to one queue has a dependency on the previous QueueSubmit on 
the other queue through an exported/imported semaphore.

From the API point of view the state of the semaphore should be changed after 
each QueueSubmit().
The problem is that it's not because of the thread and because you might have 
those 2 submission threads tied to different VkDevice/VkInstance or even 
different applications (synchronizing themselves outside the vulkan API).

Hope that makes sense.
It's not really easy to explain by mail, the best explanation is probably 
reading the test : 
https://gitlab.freedesktop.org/mesa/crucible/blob/master/src/tests/func/sync/semaphore-fd.c#L788

Like David mentioned you're not running into that issue right now, because you 
only dispatch to the thread under specific conditions.
But I could build a case to force that and likely run into the same issue.

-Lionel

On 02/08/2019 07:33, Koenig, Christian wrote:
Hi Lionel,

Well could you describe once more what the problem is?

Cause I don't fully understand why a rather normal tandem submission with two 
semaphores should fail in any way.

Regards,
Christian.

Am 02.08.2019 06:28 schrieb Lionel Landwerlin 
:
There aren't CTS tests covering the issue I was mentioning.
But we could add them.

I don't have all the details regarding your implementation but even with
the "semaphore thread", I could see it running into the same issues.
What if a mix of binary & timeline semaphores are handed to vkQueueSubmit()?

For example with queueA & queueB from 2 different VkDevice :
 vkQueueSubmit(queueA, signal semA);
 vkQueueSubmit(queueA, wait on [semA, timelineSemB]); with
timelineSemB triggering a wait before signal.
 vkQueueSubmit(queueB, signal semA);


-Lionel

On 02/08/2019 06:18, Zhou, David(ChunMing) wrote:
> Hi Lionel,
>
> By the Queue thread is a heavy thread, which is always resident in driver 
> during application running, our guys don't like that. So we switch to 
> Semaphore Thread, only when waitBeforeSignal of timeline happens, we spawn a 
> thread to handle that wait. So we don't have your this issue.
> By the way, I already pass all your CTS cases for now. I suggest you to 
> switch to Semaphore Thread instead of Queue Thread as well. It works very 
> well.
>
> -David
>
> -Original Message-
> From: Lionel Landwerlin 
> 

Re: Threaded submission & semaphore sharing

[Lionel Landwerlin]

On 02/08/2019 08:21, Koenig, Christian wrote:



Am 02.08.2019 07:17 schrieb Lionel Landwerlin 
:


On 02/08/2019 08:08, Koenig, Christian wrote:

Hi Lionel,

Well that looks more like your test case is buggy.

According to the code the ctx1 queue always waits for sem1 and
ctx2 queue always waits for sem2.


That's supposed to be the same underlying syncobj because it's
exported from one VkDevice as opaque FD from sem1 and imported
into sem2.


Well than that's still buggy and won't synchronize at all.

When ctx1 waits for a semaphore and then signals the same semaphore 
there is no guarantee that ctx2 will run in between jobs.


It's perfectly valid in this case to first run all jobs from ctx1 and 
then all jobs from ctx2.



That's not really how I see the semaphores working.

The spec describe VkSemaphore as an interface to an internal payload 
opaque to the application.



When ctx1 waits on the semaphore, it waits on the payload put there by 
the previous iteration.


Then it proceeds to signal it by replacing the internal payload.


ctx2 then waits on that and replaces the payload again with the new 
internal synchronization object.



The internal payload is a dma fence in our case and signaling just 
replaces a dma fence by another or puts one where there was none before.


So we should have created a dependecy link between all the submissions 
and then should be executed in the order of QueueSubmit() calls.



-Lionel




It only prevents running both at the same time and as far as I can see 
that still works even with threaded submission.


You need at least two semaphores for a tandem submission.

Regards,
Christian.



This way there can't be any Synchronisation between the two.

Regards,
Christian.

Am 02.08.2019 06:55 schrieb Lionel Landwerlin

:
Hey Christian,

The problem boils down to the fact that we don't immediately
create dma fences when calling vkQueueSubmit().
This is delayed to a thread.

From a single application thread, you can QueueSubmit() to 2
queues from 2 different devices.
Each QueueSubmit to one queue has a dependency on the previous
QueueSubmit on the other queue through an exported/imported
semaphore.

From the API point of view the state of the semaphore should
be changed after each QueueSubmit().
The problem is that it's not because of the thread and because
you might have those 2 submission threads tied to different
VkDevice/VkInstance or even different applications
(synchronizing themselves outside the vulkan API).

Hope that makes sense.
It's not really easy to explain by mail, the best explanation
is probably reading the test :

https://gitlab.freedesktop.org/mesa/crucible/blob/master/src/tests/func/sync/semaphore-fd.c#L788

Like David mentioned you're not running into that issue right
now, because you only dispatch to the thread under specific
conditions.
But I could build a case to force that and likely run into the
same issue.

-Lionel

On 02/08/2019 07:33, Koenig, Christian wrote:

Hi Lionel,

Well could you describe once more what the problem is?

Cause I don't fully understand why a rather normal tandem
submission with two semaphores should fail in any way.

Regards,
Christian.

Am 02.08.2019 06:28 schrieb Lionel Landwerlin

:
There aren't CTS tests covering the issue I was mentioning.
But we could add them.

I don't have all the details regarding your implementation
but even with
the "semaphore thread", I could see it running into the
same issues.
What if a mix of binary & timeline semaphores are handed
to vkQueueSubmit()?

For example with queueA & queueB from 2 different VkDevice :
 vkQueueSubmit(queueA, signal semA);
 vkQueueSubmit(queueA, wait on [semA, timelineSemB]);
with
timelineSemB triggering a wait before signal.
 vkQueueSubmit(queueB, signal semA);


-Lionel

On 02/08/2019 06:18, Zhou, David(ChunMing) wrote:
> Hi Lionel,
>
> By the Queue thread is a heavy thread, which is always
resident in driver during application running, our guys
don't like that. So we switch to Semaphore Thread, only
when waitBeforeSignal of timeline happens, we spawn a
thread to handle that wait. So we don't have your this issue.
> By the way, I already pass all your CTS cases for now. I

Re: Threaded submission & semaphore sharing

[Koenig, Christian]

Am 02.08.2019 07:17 schrieb Lionel Landwerlin :
On 02/08/2019 08:08, Koenig, Christian wrote:
Hi Lionel,

Well that looks more like your test case is buggy.

According to the code the ctx1 queue always waits for sem1 and ctx2 queue 
always waits for sem2.


That's supposed to be the same underlying syncobj because it's exported from 
one VkDevice as opaque FD from sem1 and imported into sem2.

Well than that's still buggy and won't synchronize at all.

When ctx1 waits for a semaphore and then signals the same semaphore there is no 
guarantee that ctx2 will run in between jobs.

It's perfectly valid in this case to first run all jobs from ctx1 and then all 
jobs from ctx2.

It only prevents running both at the same time and as far as I can see that 
still works even with threaded submission.

You need at least two semaphores for a tandem submission.

Regards,
Christian.


This way there can't be any Synchronisation between the two.

Regards,
Christian.

Am 02.08.2019 06:55 schrieb Lionel Landwerlin 
:
Hey Christian,

The problem boils down to the fact that we don't immediately create dma fences 
when calling vkQueueSubmit().
This is delayed to a thread.

From a single application thread, you can QueueSubmit() to 2 queues from 2 
different devices.
Each QueueSubmit to one queue has a dependency on the previous QueueSubmit on 
the other queue through an exported/imported semaphore.

From the API point of view the state of the semaphore should be changed after 
each QueueSubmit().
The problem is that it's not because of the thread and because you might have 
those 2 submission threads tied to different VkDevice/VkInstance or even 
different applications (synchronizing themselves outside the vulkan API).

Hope that makes sense.
It's not really easy to explain by mail, the best explanation is probably 
reading the test : 
https://gitlab.freedesktop.org/mesa/crucible/blob/master/src/tests/func/sync/semaphore-fd.c#L788

Like David mentioned you're not running into that issue right now, because you 
only dispatch to the thread under specific conditions.
But I could build a case to force that and likely run into the same issue.

-Lionel

On 02/08/2019 07:33, Koenig, Christian wrote:
Hi Lionel,

Well could you describe once more what the problem is?

Cause I don't fully understand why a rather normal tandem submission with two 
semaphores should fail in any way.

Regards,
Christian.

Am 02.08.2019 06:28 schrieb Lionel Landwerlin 
:
There aren't CTS tests covering the issue I was mentioning.
But we could add them.

I don't have all the details regarding your implementation but even with
the "semaphore thread", I could see it running into the same issues.
What if a mix of binary & timeline semaphores are handed to vkQueueSubmit()?

For example with queueA & queueB from 2 different VkDevice :
 vkQueueSubmit(queueA, signal semA);
 vkQueueSubmit(queueA, wait on [semA, timelineSemB]); with
timelineSemB triggering a wait before signal.
 vkQueueSubmit(queueB, signal semA);


-Lionel

On 02/08/2019 06:18, Zhou, David(ChunMing) wrote:
> Hi Lionel,
>
> By the Queue thread is a heavy thread, which is always resident in driver 
> during application running, our guys don't like that. So we switch to 
> Semaphore Thread, only when waitBeforeSignal of timeline happens, we spawn a 
> thread to handle that wait. So we don't have your this issue.
> By the way, I already pass all your CTS cases for now. I suggest you to 
> switch to Semaphore Thread instead of Queue Thread as well. It works very 
> well.
>
> -David
>
> -Original Message-
> From: Lionel Landwerlin 
> 
> Sent: Friday, August 2, 2019 4:52 AM
> To: dri-devel 
> ; 
> Koenig, Christian 
> ; Zhou, 
> David(ChunMing) ; Jason 
> Ekstrand 
> Subject: Threaded submission & semaphore sharing
>
> Hi Christian, David,
>
> Sorry to report this so late in the process, but I think we found an issue 
> not directly related to syncobj timelines themselves but with a side effect 
> of the threaded submissions.
>
> Essentially we're failing a test in crucible :
> func.sync.semaphore-fd.opaque-fd
> This test create a single binary semaphore, shares it between 2 
> VkDevice/VkQueue.
> Then in a loop it proceeds to submit workload alternating between the 2 
> VkQueue with one submit depending on the other.
> It does so by waiting on the VkSemaphore signaled in the previous iteration 
> and resignaling it.
>
> The problem for us is that once things are dispatched to the submission 
> thread, the ordering of the submission is lost.
> Because we have 2 devices and they both have their own submission thread.
>
> Jason suggested that we reestablish the ordering by having 
> semaphores/syncobjs carry an additional uint64_t payload.
> 

Re: Threaded submission & semaphore sharing

[Lionel Landwerlin]

On 02/08/2019 08:08, Koenig, Christian wrote:

Hi Lionel,

Well that looks more like your test case is buggy.

According to the code the ctx1 queue always waits for sem1 and ctx2 
queue always waits for sem2.



That's supposed to be the same underlying syncobj because it's exported 
from one VkDevice as opaque FD from sem1 and imported into sem2.





This way there can't be any Synchronisation between the two.

Regards,
Christian.

Am 02.08.2019 06:55 schrieb Lionel Landwerlin 
:

Hey Christian,

The problem boils down to the fact that we don't immediately create 
dma fences when calling vkQueueSubmit().

This is delayed to a thread.

From a single application thread, you can QueueSubmit() to 2 queues 
from 2 different devices.
Each QueueSubmit to one queue has a dependency on the previous 
QueueSubmit on the other queue through an exported/imported semaphore.


From the API point of view the state of the semaphore should be 
changed after each QueueSubmit().
The problem is that it's not because of the thread and because you 
might have those 2 submission threads tied to different 
VkDevice/VkInstance or even different applications (synchronizing 
themselves outside the vulkan API).


Hope that makes sense.
It's not really easy to explain by mail, the best explanation is 
probably reading the test : 
https://gitlab.freedesktop.org/mesa/crucible/blob/master/src/tests/func/sync/semaphore-fd.c#L788


Like David mentioned you're not running into that issue right now, 
because you only dispatch to the thread under specific conditions.

But I could build a case to force that and likely run into the same issue.

-Lionel

On 02/08/2019 07:33, Koenig, Christian wrote:

Hi Lionel,

Well could you describe once more what the problem is?

Cause I don't fully understand why a rather normal tandem submission 
with two semaphores should fail in any way.


Regards,
Christian.

Am 02.08.2019 06:28 schrieb Lionel Landwerlin 
:

There aren't CTS tests covering the issue I was mentioning.
But we could add them.

I don't have all the details regarding your implementation but even with
the "semaphore thread", I could see it running into the same issues.
What if a mix of binary & timeline semaphores are handed to 
vkQueueSubmit()?


For example with queueA & queueB from 2 different VkDevice :
 vkQueueSubmit(queueA, signal semA);
 vkQueueSubmit(queueA, wait on [semA, timelineSemB]); with
timelineSemB triggering a wait before signal.
 vkQueueSubmit(queueB, signal semA);


-Lionel

On 02/08/2019 06:18, Zhou, David(ChunMing) wrote:
> Hi Lionel,
>
> By the Queue thread is a heavy thread, which is always resident in 
driver during application running, our guys don't like that. So we 
switch to Semaphore Thread, only when waitBeforeSignal of timeline 
happens, we spawn a thread to handle that wait. So we don't have your 
this issue.
> By the way, I already pass all your CTS cases for now. I suggest 
you to switch to Semaphore Thread instead of Queue Thread as well. It 
works very well.

>
> -David
>
> -Original Message-
> From: Lionel Landwerlin 
> Sent: Friday, August 2, 2019 4:52 AM
> To: dri-devel ; Koenig, Christian 
; Zhou, David(ChunMing) 
; Jason Ekstrand 

> Subject: Threaded submission & semaphore sharing
>
> Hi Christian, David,
>
> Sorry to report this so late in the process, but I think we found 
an issue not directly related to syncobj timelines themselves but 
with a side effect of the threaded submissions.

>
> Essentially we're failing a test in crucible :
> func.sync.semaphore-fd.opaque-fd
> This test create a single binary semaphore, shares it between 2 
VkDevice/VkQueue.
> Then in a loop it proceeds to submit workload alternating between 
the 2 VkQueue with one submit depending on the other.
> It does so by waiting on the VkSemaphore signaled in the previous 
iteration and resignaling it.

>
> The problem for us is that once things are dispatched to the 
submission thread, the ordering of the submission is lost.
> Because we have 2 devices and they both have their own submission 
thread.

>
> Jason suggested that we reestablish the ordering by having 
semaphores/syncobjs carry an additional uint64_t payload.
> This 64bit integer would represent be an identifier that submission 
threads will WAIT_FOR_AVAILABLE on.

>
> The scenario would look like this :
>       - vkQueueSubmit(queueA, signal on semA);
>           - in the caller thread, this would increment the syncobj 
additional u64 payload and return it to userspace.
>           - at some point the submission thread of queueA submits 
the workload and signal the syncobj of semA with value returned in 
the caller thread of vkQueueSubmit().

>       - vkQueueSubmit(queueB, wait on semA);
>           - in the caller thread, this would read the syncobj 
additional

> u64 payload
>           - at some point the submission thread of queueB will try 
to submit the work, but first it will WAIT_FOR_AVAILABLE the u64 
value returned in the step above

Re: Threaded submission & semaphore sharing

[Koenig, Christian]

Hi Lionel,

Well that looks more like your test case is buggy.

According to the code the ctx1 queue always waits for sem1 and ctx2 queue 
always waits for sem2.

This way there can't be any Synchronisation between the two.

Regards,
Christian.

Am 02.08.2019 06:55 schrieb Lionel Landwerlin :
Hey Christian,

The problem boils down to the fact that we don't immediately create dma fences 
when calling vkQueueSubmit().
This is delayed to a thread.

>From a single application thread, you can QueueSubmit() to 2 queues from 2 
>different devices.
Each QueueSubmit to one queue has a dependency on the previous QueueSubmit on 
the other queue through an exported/imported semaphore.

>From the API point of view the state of the semaphore should be changed after 
>each QueueSubmit().
The problem is that it's not because of the thread and because you might have 
those 2 submission threads tied to different VkDevice/VkInstance or even 
different applications (synchronizing themselves outside the vulkan API).

Hope that makes sense.
It's not really easy to explain by mail, the best explanation is probably 
reading the test : 
https://gitlab.freedesktop.org/mesa/crucible/blob/master/src/tests/func/sync/semaphore-fd.c#L788

Like David mentioned you're not running into that issue right now, because you 
only dispatch to the thread under specific conditions.
But I could build a case to force that and likely run into the same issue.

-Lionel

On 02/08/2019 07:33, Koenig, Christian wrote:
Hi Lionel,

Well could you describe once more what the problem is?

Cause I don't fully understand why a rather normal tandem submission with two 
semaphores should fail in any way.

Regards,
Christian.

Am 02.08.2019 06:28 schrieb Lionel Landwerlin 
:
There aren't CTS tests covering the issue I was mentioning.
But we could add them.

I don't have all the details regarding your implementation but even with
the "semaphore thread", I could see it running into the same issues.
What if a mix of binary & timeline semaphores are handed to vkQueueSubmit()?

For example with queueA & queueB from 2 different VkDevice :
 vkQueueSubmit(queueA, signal semA);
 vkQueueSubmit(queueA, wait on [semA, timelineSemB]); with
timelineSemB triggering a wait before signal.
 vkQueueSubmit(queueB, signal semA);


-Lionel

On 02/08/2019 06:18, Zhou, David(ChunMing) wrote:
> Hi Lionel,
>
> By the Queue thread is a heavy thread, which is always resident in driver 
> during application running, our guys don't like that. So we switch to 
> Semaphore Thread, only when waitBeforeSignal of timeline happens, we spawn a 
> thread to handle that wait. So we don't have your this issue.
> By the way, I already pass all your CTS cases for now. I suggest you to 
> switch to Semaphore Thread instead of Queue Thread as well. It works very 
> well.
>
> -David
>
> -Original Message-
> From: Lionel Landwerlin 
> 
> Sent: Friday, August 2, 2019 4:52 AM
> To: dri-devel 
> ; 
> Koenig, Christian 
> ; Zhou, 
> David(ChunMing) ; Jason 
> Ekstrand 
> Subject: Threaded submission & semaphore sharing
>
> Hi Christian, David,
>
> Sorry to report this so late in the process, but I think we found an issue 
> not directly related to syncobj timelines themselves but with a side effect 
> of the threaded submissions.
>
> Essentially we're failing a test in crucible :
> func.sync.semaphore-fd.opaque-fd
> This test create a single binary semaphore, shares it between 2 
> VkDevice/VkQueue.
> Then in a loop it proceeds to submit workload alternating between the 2 
> VkQueue with one submit depending on the other.
> It does so by waiting on the VkSemaphore signaled in the previous iteration 
> and resignaling it.
>
> The problem for us is that once things are dispatched to the submission 
> thread, the ordering of the submission is lost.
> Because we have 2 devices and they both have their own submission thread.
>
> Jason suggested that we reestablish the ordering by having 
> semaphores/syncobjs carry an additional uint64_t payload.
> This 64bit integer would represent be an identifier that submission threads 
> will WAIT_FOR_AVAILABLE on.
>
> The scenario would look like this :
>   - vkQueueSubmit(queueA, signal on semA);
>   - in the caller thread, this would increment the syncobj additional 
> u64 payload and return it to userspace.
>   - at some point the submission thread of queueA submits the 
> workload and signal the syncobj of semA with value returned in the caller 
> thread of vkQueueSubmit().
>   - vkQueueSubmit(queueB, wait on semA);
>   - in the caller thread, this would read the syncobj additional
> u64 payload
>   - at some point the submission thread of queueB will try to submit 
> the work, but first it will 

Re: Threaded submission & semaphore sharing

[Lionel Landwerlin]

Hey Christian,

The problem boils down to the fact that we don't immediately create dma 
fences when calling vkQueueSubmit().

This is delayed to a thread.

From a single application thread, you can QueueSubmit() to 2 queues 
from 2 different devices.
Each QueueSubmit to one queue has a dependency on the previous 
QueueSubmit on the other queue through an exported/imported semaphore.


From the API point of view the state of the semaphore should be changed 
after each QueueSubmit().
The problem is that it's not because of the thread and because you might 
have those 2 submission threads tied to different VkDevice/VkInstance or 
even different applications (synchronizing themselves outside the vulkan 
API).


Hope that makes sense.
It's not really easy to explain by mail, the best explanation is 
probably reading the test : 
https://gitlab.freedesktop.org/mesa/crucible/blob/master/src/tests/func/sync/semaphore-fd.c#L788


Like David mentioned you're not running into that issue right now, 
because you only dispatch to the thread under specific conditions.

But I could build a case to force that and likely run into the same issue.

-Lionel

On 02/08/2019 07:33, Koenig, Christian wrote:

Hi Lionel,

Well could you describe once more what the problem is?

Cause I don't fully understand why a rather normal tandem submission 
with two semaphores should fail in any way.


Regards,
Christian.

Am 02.08.2019 06:28 schrieb Lionel Landwerlin 
:

There aren't CTS tests covering the issue I was mentioning.
But we could add them.

I don't have all the details regarding your implementation but even with
the "semaphore thread", I could see it running into the same issues.
What if a mix of binary & timeline semaphores are handed to 
vkQueueSubmit()?


For example with queueA & queueB from 2 different VkDevice :
 vkQueueSubmit(queueA, signal semA);
 vkQueueSubmit(queueA, wait on [semA, timelineSemB]); with
timelineSemB triggering a wait before signal.
 vkQueueSubmit(queueB, signal semA);


-Lionel

On 02/08/2019 06:18, Zhou, David(ChunMing) wrote:
> Hi Lionel,
>
> By the Queue thread is a heavy thread, which is always resident in 
driver during application running, our guys don't like that. So we 
switch to Semaphore Thread, only when waitBeforeSignal of timeline 
happens, we spawn a thread to handle that wait. So we don't have your 
this issue.
> By the way, I already pass all your CTS cases for now. I suggest you 
to switch to Semaphore Thread instead of Queue Thread as well. It 
works very well.

>
> -David
>
> -Original Message-
> From: Lionel Landwerlin 
> Sent: Friday, August 2, 2019 4:52 AM
> To: dri-devel ; Koenig, Christian 
; Zhou, David(ChunMing) 
; Jason Ekstrand 

> Subject: Threaded submission & semaphore sharing
>
> Hi Christian, David,
>
> Sorry to report this so late in the process, but I think we found an 
issue not directly related to syncobj timelines themselves but with a 
side effect of the threaded submissions.

>
> Essentially we're failing a test in crucible :
> func.sync.semaphore-fd.opaque-fd
> This test create a single binary semaphore, shares it between 2 
VkDevice/VkQueue.
> Then in a loop it proceeds to submit workload alternating between 
the 2 VkQueue with one submit depending on the other.
> It does so by waiting on the VkSemaphore signaled in the previous 
iteration and resignaling it.

>
> The problem for us is that once things are dispatched to the 
submission thread, the ordering of the submission is lost.
> Because we have 2 devices and they both have their own submission 
thread.

>
> Jason suggested that we reestablish the ordering by having 
semaphores/syncobjs carry an additional uint64_t payload.
> This 64bit integer would represent be an identifier that submission 
threads will WAIT_FOR_AVAILABLE on.

>
> The scenario would look like this :
>       - vkQueueSubmit(queueA, signal on semA);
>           - in the caller thread, this would increment the syncobj 
additional u64 payload and return it to userspace.
>           - at some point the submission thread of queueA submits 
the workload and signal the syncobj of semA with value returned in the 
caller thread of vkQueueSubmit().

>       - vkQueueSubmit(queueB, wait on semA);
>           - in the caller thread, this would read the syncobj additional
> u64 payload
>           - at some point the submission thread of queueB will try 
to submit the work, but first it will WAIT_FOR_AVAILABLE the u64 value 
returned in the step above

>
> Because we want the binary semaphores to be shared across processes 
and would like this to remain a single FD, the simplest location to 
store this additional u64 payload would be the DRM syncobj.

> It would need an additional ioctl to read & increment the value.
>
> What do you think?
>
> -Lionel




___
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: Threaded submission & semaphore sharing

[Koenig, Christian]

Hi Lionel,

Well could you describe once more what the problem is?

Cause I don't fully understand why a rather normal tandem submission with two 
semaphores should fail in any way.

Regards,
Christian.

Am 02.08.2019 06:28 schrieb Lionel Landwerlin :
There aren't CTS tests covering the issue I was mentioning.
But we could add them.

I don't have all the details regarding your implementation but even with
the "semaphore thread", I could see it running into the same issues.
What if a mix of binary & timeline semaphores are handed to vkQueueSubmit()?

For example with queueA & queueB from 2 different VkDevice :
 vkQueueSubmit(queueA, signal semA);
 vkQueueSubmit(queueA, wait on [semA, timelineSemB]); with
timelineSemB triggering a wait before signal.
 vkQueueSubmit(queueB, signal semA);


-Lionel

On 02/08/2019 06:18, Zhou, David(ChunMing) wrote:
> Hi Lionel,
>
> By the Queue thread is a heavy thread, which is always resident in driver 
> during application running, our guys don't like that. So we switch to 
> Semaphore Thread, only when waitBeforeSignal of timeline happens, we spawn a 
> thread to handle that wait. So we don't have your this issue.
> By the way, I already pass all your CTS cases for now. I suggest you to 
> switch to Semaphore Thread instead of Queue Thread as well. It works very 
> well.
>
> -David
>
> -Original Message-
> From: Lionel Landwerlin 
> Sent: Friday, August 2, 2019 4:52 AM
> To: dri-devel ; Koenig, Christian 
> ; Zhou, David(ChunMing) ; 
> Jason Ekstrand 
> Subject: Threaded submission & semaphore sharing
>
> Hi Christian, David,
>
> Sorry to report this so late in the process, but I think we found an issue 
> not directly related to syncobj timelines themselves but with a side effect 
> of the threaded submissions.
>
> Essentially we're failing a test in crucible :
> func.sync.semaphore-fd.opaque-fd
> This test create a single binary semaphore, shares it between 2 
> VkDevice/VkQueue.
> Then in a loop it proceeds to submit workload alternating between the 2 
> VkQueue with one submit depending on the other.
> It does so by waiting on the VkSemaphore signaled in the previous iteration 
> and resignaling it.
>
> The problem for us is that once things are dispatched to the submission 
> thread, the ordering of the submission is lost.
> Because we have 2 devices and they both have their own submission thread.
>
> Jason suggested that we reestablish the ordering by having 
> semaphores/syncobjs carry an additional uint64_t payload.
> This 64bit integer would represent be an identifier that submission threads 
> will WAIT_FOR_AVAILABLE on.
>
> The scenario would look like this :
>   - vkQueueSubmit(queueA, signal on semA);
>   - in the caller thread, this would increment the syncobj additional 
> u64 payload and return it to userspace.
>   - at some point the submission thread of queueA submits the 
> workload and signal the syncobj of semA with value returned in the caller 
> thread of vkQueueSubmit().
>   - vkQueueSubmit(queueB, wait on semA);
>   - in the caller thread, this would read the syncobj additional
> u64 payload
>   - at some point the submission thread of queueB will try to submit 
> the work, but first it will WAIT_FOR_AVAILABLE the u64 value returned in the 
> step above
>
> Because we want the binary semaphores to be shared across processes and would 
> like this to remain a single FD, the simplest location to store this 
> additional u64 payload would be the DRM syncobj.
> It would need an additional ioctl to read & increment the value.
>
> What do you think?
>
> -Lionel


___
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: Threaded submission & semaphore sharing

[Lionel Landwerlin]

There aren't CTS tests covering the issue I was mentioning.
But we could add them.

I don't have all the details regarding your implementation but even with 
the "semaphore thread", I could see it running into the same issues.

What if a mix of binary & timeline semaphores are handed to vkQueueSubmit()?

For example with queueA & queueB from 2 different VkDevice :
    vkQueueSubmit(queueA, signal semA);
    vkQueueSubmit(queueA, wait on [semA, timelineSemB]); with 
timelineSemB triggering a wait before signal.

    vkQueueSubmit(queueB, signal semA);


-Lionel

On 02/08/2019 06:18, Zhou, David(ChunMing) wrote:

Hi Lionel,

By the Queue thread is a heavy thread, which is always resident in driver 
during application running, our guys don't like that. So we switch to Semaphore 
Thread, only when waitBeforeSignal of timeline happens, we spawn a thread to 
handle that wait. So we don't have your this issue.
By the way, I already pass all your CTS cases for now. I suggest you to switch 
to Semaphore Thread instead of Queue Thread as well. It works very well.

-David

-Original Message-
From: Lionel Landwerlin 
Sent: Friday, August 2, 2019 4:52 AM
To: dri-devel ; Koenig, Christian 
; Zhou, David(ChunMing) ; Jason Ekstrand 

Subject: Threaded submission & semaphore sharing

Hi Christian, David,

Sorry to report this so late in the process, but I think we found an issue not 
directly related to syncobj timelines themselves but with a side effect of the 
threaded submissions.

Essentially we're failing a test in crucible :
func.sync.semaphore-fd.opaque-fd
This test create a single binary semaphore, shares it between 2 
VkDevice/VkQueue.
Then in a loop it proceeds to submit workload alternating between the 2 VkQueue 
with one submit depending on the other.
It does so by waiting on the VkSemaphore signaled in the previous iteration and 
resignaling it.

The problem for us is that once things are dispatched to the submission thread, 
the ordering of the submission is lost.
Because we have 2 devices and they both have their own submission thread.

Jason suggested that we reestablish the ordering by having semaphores/syncobjs 
carry an additional uint64_t payload.
This 64bit integer would represent be an identifier that submission threads 
will WAIT_FOR_AVAILABLE on.

The scenario would look like this :
      - vkQueueSubmit(queueA, signal on semA);
          - in the caller thread, this would increment the syncobj additional 
u64 payload and return it to userspace.
          - at some point the submission thread of queueA submits the workload 
and signal the syncobj of semA with value returned in the caller thread of 
vkQueueSubmit().
      - vkQueueSubmit(queueB, wait on semA);
          - in the caller thread, this would read the syncobj additional
u64 payload
          - at some point the submission thread of queueB will try to submit 
the work, but first it will WAIT_FOR_AVAILABLE the u64 value returned in the 
step above

Because we want the binary semaphores to be shared across processes and would 
like this to remain a single FD, the simplest location to store this additional 
u64 payload would be the DRM syncobj.
It would need an additional ioctl to read & increment the value.

What do you think?

-Lionel



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RE: Threaded submission & semaphore sharing

[Zhou, David(ChunMing)]

Hi Lionel,

By the Queue thread is a heavy thread, which is always resident in driver 
during application running, our guys don't like that. So we switch to Semaphore 
Thread, only when waitBeforeSignal of timeline happens, we spawn a thread to 
handle that wait. So we don't have your this issue.
By the way, I already pass all your CTS cases for now. I suggest you to switch 
to Semaphore Thread instead of Queue Thread as well. It works very well.

-David

-Original Message-
From: Lionel Landwerlin  
Sent: Friday, August 2, 2019 4:52 AM
To: dri-devel ; Koenig, Christian 
; Zhou, David(ChunMing) ; Jason 
Ekstrand 
Subject: Threaded submission & semaphore sharing

Hi Christian, David,

Sorry to report this so late in the process, but I think we found an issue not 
directly related to syncobj timelines themselves but with a side effect of the 
threaded submissions.

Essentially we're failing a test in crucible : 
func.sync.semaphore-fd.opaque-fd
This test create a single binary semaphore, shares it between 2 
VkDevice/VkQueue.
Then in a loop it proceeds to submit workload alternating between the 2 VkQueue 
with one submit depending on the other.
It does so by waiting on the VkSemaphore signaled in the previous iteration and 
resignaling it.

The problem for us is that once things are dispatched to the submission thread, 
the ordering of the submission is lost.
Because we have 2 devices and they both have their own submission thread.

Jason suggested that we reestablish the ordering by having semaphores/syncobjs 
carry an additional uint64_t payload.
This 64bit integer would represent be an identifier that submission threads 
will WAIT_FOR_AVAILABLE on.

The scenario would look like this :
     - vkQueueSubmit(queueA, signal on semA);
         - in the caller thread, this would increment the syncobj additional 
u64 payload and return it to userspace.
         - at some point the submission thread of queueA submits the workload 
and signal the syncobj of semA with value returned in the caller thread of 
vkQueueSubmit().
     - vkQueueSubmit(queueB, wait on semA);
         - in the caller thread, this would read the syncobj additional
u64 payload
         - at some point the submission thread of queueB will try to submit the 
work, but first it will WAIT_FOR_AVAILABLE the u64 value returned in the step 
above

Because we want the binary semaphores to be shared across processes and would 
like this to remain a single FD, the simplest location to store this additional 
u64 payload would be the DRM syncobj.
It would need an additional ioctl to read & increment the value.

What do you think?

-Lionel
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