From 4965af4364c6af1ccc9c981542e11d38dac082de Mon Sep 17 00:00:00 2001
From: Someone Serge <sergei.kozlukov@aalto.fi>
Date: Wed, 13 Apr 2022 03:09:51 +0300
Subject: [PATCH] nvidia-thrust: explain (host|device)System

---
 .../libraries/nvidia-thrust/default.nix            | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/pkgs/development/libraries/nvidia-thrust/default.nix b/pkgs/development/libraries/nvidia-thrust/default.nix
index 1c673837c28c..545607ead2d1 100644
--- a/pkgs/development/libraries/nvidia-thrust/default.nix
+++ b/pkgs/development/libraries/nvidia-thrust/default.nix
@@ -7,12 +7,20 @@
 , cudaPackages
 , symlinkJoin
 , tbb
-  # Upstream defaults:
 , hostSystem ? "CPP"
-, deviceSystem ? if config.cudaSupport or false then "CUDA" else "CPP"
+, deviceSystem ? if config.cudaSupport or false then "CUDA" else "OMP"
 }:
 
-assert builtins.elem deviceSystem [ "CPP" "OMP" "TBB" "CUDA" ];
+# Policy for device_vector<T>
+assert builtins.elem deviceSystem [
+  "CPP" # Serial on CPU
+  "OMP" # Parallel with OpenMP
+  "TBB" # Parallel with Intel TBB
+  "CUDA" # Parallel on GPU
+];
+
+# Policy for host_vector<T>
+# Always lives on CPU, but execution can be made parallel
 assert builtins.elem hostSystem [ "CPP" "OMP" "TBB" ];
 
 let