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
<lionel.g.landwer...@intel.com>:
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.landwer...@intel.com>
> Sent: Friday, August 2, 2019 4:52 AM
> To: dri-devel <dri-devel@lists.freedesktop.org>; Koenig, Christian
<christian.koe...@amd.com>; Zhou, David(ChunMing)
<david1.z...@amd.com>; Jason Ekstrand <ja...@jlekstrand.net>
> 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