Am 20.06.23 um 10:28 schrieb Boris Brezillon:
On Tue, 20 Jun 2023 10:12:13 +0200
Christian König <ckoenig.leichtzumerken@xxxxxxxxx> wrote:
I think Boris's suggestion of having this through a common
DRM_EXEC_FLAG_ALLOW_DUPLICATES flag fits well.
No, again. The only driver which should accept duplicates is radeon, for
all other drivers especially new ones duplicates should probably be
rejected.
We only allow this for radeon because it is already UAPI, could be that
we need to do this for amdgpu as well but I really hope we don't need this.
Just want to describe the use case we have: we support submission in
batch (several jobs passed to the submit ioctl) with a
submit-all-or-nothing model: if any of the job description is passed
wrong args or causes an allocation error, we fail the whole group. In
the submission path, we want to prepare GEMs for all jobs. That means
adding enough fence slots for the number job finished fences. Given not
all jobs will access the same set of BOs, I thought I could use
duplicates support to make my life easier, because otherwise I have to
collect all BOs upfront, store them in a temporary array, and keep
track of the number of fence slots needed for each of them. I guess
the other option would be to over-estimate the number of slots and make
it equal to num_jobs for all BOs.
Sounds pretty much what amdgpu is doing as well, but question is why
don't you give just one list of BOs? Do you really want to add the
fences that fine grained?
For radeon it turned out that we just had stupid userspace which
sometimes mentioned a BO in the list twice.
On the other hand over estimating the number of fences needed is
perfectly fine as well, that is rounded up to the next kvmalloc size or
even next page size anyway.
So IIRC and you have <510 fences you either get 14, 30, 62, 126, 254 and
above 510 you should get it rounded to the next 512.
Regards,
Christian.
