nvgpu: gk20a: Optimize vm_put_buffers for zero buffers

Return immediately in case there are no buffers to put. This skips
acquiring mutexes and map batch start/finish overheads.

Bug 1614735
Bug 1623949
Bug 1660392

Change-Id: Ief04e36d995e65c1510496c17cb3f5bb90486c69
Signed-off-by: Sami Kiminki <skiminki@nvidia.com>
Reviewed-on: http://git-master/r/815376
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Tested-by: Terje Bergstrom <tbergstrom@nvidia.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/gk20a/mm_gk20a.c b/drivers/gpu/nvgpu/gk20a/mm_gk20a.c
index 334f251c..4b06ff3c 100644
--- a/drivers/gpu/nvgpu/gk20a/mm_gk20a.c
+++ b/drivers/gpu/nvgpu/gk20a/mm_gk20a.c
@@ -827,6 +827,9 @@ void gk20a_vm_put_buffers(struct vm_gk20a *vm,
         int i;
         struct vm_gk20a_mapping_batch batch;
 
+        if (num_buffers == 0)
+                return;
+
         mutex_lock(&vm->update_gmmu_lock);
         gk20a_vm_mapping_batch_start(&batch);
         vm->kref_put_batch = &batch;