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
<lionel.g.landwerlin@xxxxxxxxx>
> Sent: Friday, August 2, 2019 4:52 AM
> To: dri-devel
<dri-devel@xxxxxxxxxxxxxxxxxxxxx>;
Koenig, Christian
<Christian.Koenig@xxxxxxx>; Zhou,
David(ChunMing)
<David1.Zhou@xxxxxxx>; Jason Ekstrand
<jason@xxxxxxxxxxxxxx>
> 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
