On Tue, Jul 13, 2021 at 6:51 PM Rob Clark <robdclark@xxxxxxxxx> wrote: > > On Mon, Jul 12, 2021 at 1:02 PM Daniel Vetter <daniel.vetter@xxxxxxxx> wrote: > > > > There's only one exclusive slot, and we must not break the ordering. > > > > Adding a new exclusive fence drops all previous fences from the > > dma_resv. To avoid violating the signalling order we err on the side of > > over-synchronizing by waiting for the existing fences, even if > > userspace asked us to ignore them. > > > > A better fix would be to us a dma_fence_chain or _array like e.g. > > amdgpu now uses, but > > - msm has a synchronous dma_fence_wait for anything from another > > context, so doesn't seem to care much, > > - and it probably makes sense to lift this into dma-resv.c code as a > > proper concept, so that drivers don't have to hack up their own > > solution each on their own. > > > > v2: Improve commit message per Lucas' suggestion. > > > > Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx> > > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> > > Cc: Rob Clark <robdclark@xxxxxxxxx> > > Cc: Sean Paul <sean@xxxxxxxxxx> > > Cc: linux-arm-msm@xxxxxxxxxxxxxxx > > Cc: freedreno@xxxxxxxxxxxxxxxxxxxxx > > --- > > drivers/gpu/drm/msm/msm_gem_submit.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c > > index b71da71a3dd8..edd0051d849f 100644 > > --- a/drivers/gpu/drm/msm/msm_gem_submit.c > > +++ b/drivers/gpu/drm/msm/msm_gem_submit.c > > @@ -306,7 +306,8 @@ static int submit_fence_sync(struct msm_gem_submit *submit, bool no_implicit) > > return ret; > > } > > > > - if (no_implicit) > > + /* exclusive fences must be ordered */ > > + if (no_implicit && !write) > > continue; > > In practice, modern userspace (the kind that is more likely to set the > no-implicit flag on every submit) also sets MSM_SUBMIT_BO_WRITE on > every bo, to shave some cpu overhead so I suppose this would not > really hurt anything > > Do you know if this is covered in any piglit/etc test? You need some command submission, plus buffer sharing with vgem setting it's own exclusive fences, plus checking with dma_buf poll() whether it signals all in the right order. That's pretty low-level, so maybe something in igt, but I haven't typed that. Maybe I need to do that for i915 at least. -Daniel > BR, > -R > > > > > ret = msm_gem_sync_object(&msm_obj->base, submit->ring->fctx, > > -- > > 2.32.0 > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
