From e1a0bff43c53dfa6d456698da6294cdac4a5fdd4 Mon Sep 17 00:00:00 2001
From: CGH0S7 <776459475@qq.com>
Date: Thu, 9 Apr 2026 21:20:45 +0800
Subject: [PATCH] Reduce redundant GPU host buffer preparation

---
 AMSS_NCKU_source/bssn_cuda_ops.cu | 15 +++++++++++----
 AMSS_NCKU_source/bssn_cuda_step.C | 20 --------------------
 2 files changed, 11 insertions(+), 24 deletions(-)

diff --git a/AMSS_NCKU_source/bssn_cuda_ops.cu b/AMSS_NCKU_source/bssn_cuda_ops.cu
index 45fb588..be62fed 100644
--- a/AMSS_NCKU_source/bssn_cuda_ops.cu
+++ b/AMSS_NCKU_source/bssn_cuda_ops.cu
@@ -787,12 +787,19 @@ int bssn_cuda_rk4_boundary_var(int *ex, double dT,
   const bool refresh_rhs =
       (rk_stage == 0) || !cache.rhs_resident || cache.host_rhs != rhs_accum;
   double *stage_ptr = nullptr;
+  const double *mapped_state0_ptr = refresh_state0 ? bssn_gpu_find_device_buffer(state0) : cache.state0.ptr;
+  const double *mapped_boundary_ptr = need_boundary_input ? bssn_gpu_find_device_buffer(boundary_src) : nullptr;
   const double *mapped_stage_ptr = need_stage_input ? bssn_gpu_find_device_buffer(stage_data) : nullptr;
+  const double *mapped_rhs_ptr = refresh_rhs ? bssn_gpu_find_device_buffer(rhs_accum) : cache.rhs.ptr;
 
-  bssn_gpu_prepare_host_buffer(state0, n);
-  if (need_boundary_input) bssn_gpu_prepare_host_buffer(boundary_src, n);
-  if (need_stage_input) bssn_gpu_prepare_host_buffer(stage_data, n);
-  bssn_gpu_prepare_host_buffer(rhs_accum, n);
+  if (refresh_state0 && !mapped_state0_ptr)
+    bssn_gpu_prepare_host_buffer(state0, n);
+  if (need_boundary_input && !mapped_boundary_ptr)
+    bssn_gpu_prepare_host_buffer(boundary_src, n);
+  if (need_stage_input && !mapped_stage_ptr)
+    bssn_gpu_prepare_host_buffer(stage_data, n);
+  if (refresh_rhs && !mapped_rhs_ptr)
+    bssn_gpu_prepare_host_buffer(rhs_accum, n);
 
   ok = ok &&
        (!refresh_state0 || copy_to_device_preferring_device(cache.state0, state0, bytes)) &&
diff --git a/AMSS_NCKU_source/bssn_cuda_step.C b/AMSS_NCKU_source/bssn_cuda_step.C
index 51f488b..c5ea4c6 100644
--- a/AMSS_NCKU_source/bssn_cuda_step.C
+++ b/AMSS_NCKU_source/bssn_cuda_step.C
@@ -124,25 +124,6 @@ void bssn_class::Step_MainPath_GPU(int lev, int YN)
         }
       };
 
-  auto stage_upload_var_list =
-      [&](Block *cg, MyList<var> *var_list) {
-        const int n = cg->shape[0] * cg->shape[1] * cg->shape[2];
-        while (var_list)
-        {
-          if (bssn_gpu_stage_upload_buffer(cg->fgfs[var_list->data->sgfn], n))
-          {
-            cerr << "GPU state upload failure: lev=" << lev
-                 << " var=" << var_list->data->name
-                 << " bbox=(" << cg->bbox[0] << ":" << cg->bbox[3] << ","
-                 << cg->bbox[1] << ":" << cg->bbox[4] << ","
-                 << cg->bbox[2] << ":" << cg->bbox[5] << ")" << endl;
-            ERROR = 1;
-            break;
-          }
-          var_list = var_list->next;
-        }
-      };
-
   auto ensure_stage_device_var_list =
       [&](Block *cg, MyList<var> *var_list) {
         const int n = cg->shape[0] * cg->shape[1] * cg->shape[2];
@@ -340,7 +321,6 @@ void bssn_class::Step_MainPath_GPU(int lev, int YN)
       Block *cg = BP->data;
       if (myrank == cg->rank)
       {
-        stage_upload_var_list(cg, StateList);
         if (gpu_rhs(CALLED_BY_STEP, myrank, RHS_PARA_CALLED_FIRST_TIME))
           ERROR = 1;