Use memcpy instead of std::copy when bridging images (#565) (#585)

While testing ros <-> gz communication using the bridge I noticed that the bridge was talking quite a bit of time copying images from Gazebo to ROS. I found that the std::copy operation that we're doing is substantially slower than the memcpy alternative. I think that in principle this shouldn't happen but the numbers are quite clear. Perhaps std::copy is doing something that doesn't use cache effectively --------- Signed-off-by: Carlos Agüero <[email protected]> Signed-off-by: Carlos Agüero <[email protected]> Co-authored-by: Jose Luis Rivero <[email protected]> (cherry picked from commit a781b78) Co-authored-by: Carlos Agüero <[email protected]>
gazebosim · Aug 1, 2024 · 7314ab4 · 7314ab4
1 parent c8e5742
commit 7314ab4
Showing 1 changed file with 4 additions and 6 deletions.
diff --git a/ros_gz_bridge/src/convert/sensor_msgs.cpp b/ros_gz_bridge/src/convert/sensor_msgs.cpp
@@ -166,13 +166,11 @@ convert_gz_to_ros(
 
   ros_msg.is_bigendian = false;
   ros_msg.step = ros_msg.width * num_channels * octets_per_channel;
-
-  auto count = ros_msg.step * ros_msg.height;
   ros_msg.data.resize(ros_msg.step * ros_msg.height);
-  std::copy(
-    gz_msg.data().begin(),
-    gz_msg.data().begin() + count,
-    ros_msg.data.begin());
+
+  // Prefer memcpy over std::copy for performance reasons,
+  // see https://github.com/gazebosim/ros_gz/pull/565
+  memcpy(ros_msg.data.data(), gz_msg.data().c_str(), gz_msg.data().size());
 }
 
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