spam nvrtc options (csarofeen#1783)

TORCH_WARN on nvrtc debug option impacting performance.

Author: jjsjann123

torch/csrc/jit/codegen/cuda/executor_utils.cpp

@@ -1007,6 +1007,12 @@ std::pair<NvrtcFunction, std::string> nvrtcCompile(
   if (ptxas_opt_level) {
     int val = atoi(ptxas_opt_level);
     if (val <= 4 && val >= 0) {
+      if (val < 4) {
+        TORCH_WARN(
+            "ptxas optimization level manually set as ",
+            val,
+            ", which could negatively affect performance. Try removing env variable PYTORCH_NVFUSER_JIT_OPT_LEVEL for optimal performance.");
+      }
       if (compile_to_sass) {
         jit_opt_level += std::to_string(val);
         args.push_back("--ptxas-options");

torch/csrc/jit/codegen/cuda/utils.cpp

@@ -123,6 +123,8 @@ auto parseDisableOptions() {
       } else if (token == "fallback") {
         options_map[DisableOption::Fallback] = true;
       } else if (token == "fma") {
+        TORCH_WARN(
+            "fmad is disabled for nvrtc, which could negatively affect performance. Try removing `fma` from env variable PYTORCH_NVFUSER_DISABLE for optimal performance.");
         options_map[DisableOption::Fma] = true;
       } else if (token == "index_hoist") {
         options_map[DisableOption::IndexHoist] = true;