On Mon, Aug 17, 2026 at 4:55 PM David Rosca <[email protected]> wrote:
>
>
> On 8/14/26 19:29, Alex Deucher wrote:
> > If we end up emitting a VM fence keep pipeline sync
> > associated with that fence. If not, emit them as
> > part of the IB fence.
> >
> > v2: fix need_pipe_sync handling
> >
> > Cc: David Rosca <[email protected]>
> > Fixes: cb1e657ccac8 ("drm/amdgpu: handle GDS and SPM without a VM fence")
> > Signed-off-by: Alex Deucher <[email protected]>
> > ---
> > drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c | 6 +++++-
> > drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 8 +++++---
> > drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h | 2 +-
> > 3 files changed, 11 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
> > index da4dc489e80bd..360e6f00cb7c0 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
> > @@ -222,7 +222,7 @@ int amdgpu_ib_schedule(struct amdgpu_ring *ring,
> > unsigned int num_ibs,
> > vm_af = job->hw_vm_fence;
> > /* VM sequence */
> > vm_af->ib_wptr = ring->wptr;
> > - amdgpu_vm_flush(ring, job, need_pipe_sync, &emit_spm_needed,
> > + amdgpu_vm_flush(ring, job, &need_pipe_sync, &emit_spm_needed,
> > &emit_gds_needed);
> > vm_af->ib_dw_size =
> > amdgpu_ring_get_dw_distance(ring, vm_af->ib_wptr,
> > ring->wptr);
> > @@ -235,6 +235,10 @@ int amdgpu_ib_schedule(struct amdgpu_ring *ring,
> > unsigned int num_ibs,
> > if (ring->funcs->insert_start)
> > ring->funcs->insert_start(ring);
> >
> > + /* this may have been handled by amdgpu_vm_flush */
> > + if (need_pipe_sync)
> > + amdgpu_ring_emit_pipeline_sync(ring);
> > +
> > if (emit_spm_needed)
> > adev->gfx.rlc.funcs->update_spm_vmid(adev, ring->xcc_id,
> > ring, job->vmid);
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > index 71050a86bcc3a..b7d0461184d62 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > @@ -772,7 +772,7 @@ bool amdgpu_vm_need_pipeline_sync(struct amdgpu_ring
> > *ring,
> > * Emit a VM flush when it is necessary.
> > */
> > void amdgpu_vm_flush(struct amdgpu_ring *ring, struct amdgpu_job *job,
> > - bool need_pipe_sync, bool *emit_spm_needed,
> > + bool *need_pipe_sync, bool *emit_spm_needed,
> > bool *emit_gds_needed)
> > {
> > struct amdgpu_device *adev = ring->adev;
> > @@ -827,7 +827,7 @@ void amdgpu_vm_flush(struct amdgpu_ring *ring, struct
> > amdgpu_job *job,
> > if (gds_switch_needed && emit_fence)
> > *emit_gds_needed = false;
> >
> > - if (!vm_flush_needed && !gds_switch_needed && !need_pipe_sync &&
> > + if (!vm_flush_needed && !gds_switch_needed && !(*need_pipe_sync) &&
>
> The only time need_pipe_sync in this check makes a difference is when
> only pasid_mapping_needed (which is missing from this condition, is that
> intended?) is true and the rest *_needed are false. Then emit_fence is
> true and pipeline_sync is emitted in this function which looks fine.
>
> If pasid_mapping_needed and all other *_needed are false, then
> emit_fence is false and the rest of the function effectively does
> nothing. emit_pipeline_sync will be called from amdgpu_ib_schedule.
> While this works, I think it would be better to return early here?
I see what you are saying. I think this could be simplified to
if (!emit_fence)
return;
If we are not emitting the fence, everything needs to be handled in
amdgpu_ib_schedule().
Alex
>
> David
>
> > !cleaner_shader_needed && !spm_update_needed)
> > return;
> >
> > @@ -847,8 +847,10 @@ void amdgpu_vm_flush(struct amdgpu_ring *ring, struct
> > amdgpu_job *job,
> > patch = amdgpu_ring_init_cond_exec(ring,
> > ring->cond_exe_gpu_addr);
> >
> > - if (need_pipe_sync)
> > + if (emit_fence && *need_pipe_sync) {
> > amdgpu_ring_emit_pipeline_sync(ring);
> > + *need_pipe_sync = false;
> > + }
> >
> > if (cleaner_shader_needed)
> > ring->funcs->emit_cleaner_shader(ring);
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> > index 7f2ba728e3ed3..d32183cd9e0fc 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> > @@ -512,7 +512,7 @@ int amdgpu_vm_validate(struct amdgpu_device *adev,
> > struct amdgpu_vm *vm,
> > int (*callback)(void *p, struct amdgpu_bo *bo),
> > void *param);
> > void amdgpu_vm_flush(struct amdgpu_ring *ring, struct amdgpu_job *job,
> > - bool need_pipe_sync, bool *emit_spm_needed,
> > + bool *need_pipe_sync, bool *emit_spm_needed,
> > bool *emit_gds_needed);
> > int amdgpu_vm_update_pdes(struct amdgpu_device *adev,
> > struct amdgpu_vm *vm, bool immediate);
