what's gdrcopy sync’s advantage?

[nope8]

when set env NCCL_GDRCOPY_SYNC_ENABLE=1， as I know that gdrcopy memory is device memory that host can access directly.
If enable gdrcopy sync feature, send conn head， recv conn tail will use gdrcopy memory, otherwise， send conn head，recv conn tail will use device memory that host can access directly.

what is the advantage of use gdrcopy memory compare with device memory?

gdcSync