Re: [PATCH v2 1/1] drm/amdgpu: Update PDEs flush TLB if PTB/PDB moved

[Lazar, Lijo]

On 6/2/2022 6:50 PM, Philip Yang wrote:

Flush TLBs when existing PDEs are updated because a PTB or PDB moved,
but avoids unnecessary TLB flushes when new PDBs or PTBs are added to
the page table, which commonly happens when memory is mapped for the
first time.

Suggested-by: Christian König <christian.koe...@amd.com>
Signed-off-by: Philip Yang <philip.y...@amd.com>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 8 ++++++--
  1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index 9596c22fded6..1ea204218903 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -737,6 +737,7 @@ int amdgpu_vm_update_pdes(struct amdgpu_device *adev,
  {
        struct amdgpu_vm_update_params params;
        struct amdgpu_vm_bo_base *entry;
+       bool flush_tlb_needed = false;
        int r, idx;

if (list_empty(&vm->relocated))

@@ -755,6 +756,9 @@ int amdgpu_vm_update_pdes(struct amdgpu_device *adev,
                goto error;

list_for_each_entry(entry, &vm->relocated, vm_status) {

+               /* vm_flush_needed after updating moved PDEs */
+               flush_tlb_needed |= entry->moved;

That is a strange thing to do for a bool variable. Why not just assign it?

Thanks,
Lijo

+
                r = amdgpu_vm_pde_update(&params, entry);
                if (r)
                        goto error;
@@ -764,8 +768,8 @@ int amdgpu_vm_update_pdes(struct amdgpu_device *adev,
        if (r)
                goto error;

- /* vm_flush_needed after updating PDEs */

-       atomic64_inc(&vm->tlb_seq);
+       if (flush_tlb_needed)
+               atomic64_inc(&vm->tlb_seq);

while (!list_empty(&vm->relocated)) {

                entry = list_first_entry(&vm->relocated,