Correct the install command, static library name and typo in nccl.cmake.

[Xreki]

I try to build nccl manually, using make CUDA_HOME=$CUDA_ROOT, and I get the following outputs:

$ make CUDA_HOME=$CUDA_ROOT
Compiling src/libwrap.cu                      > /home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/obj/libwrap.o
Compiling src/core.cu                         > /home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/obj/core.o
Compiling src/all_gather.cu                   > /home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/obj/all_gather.o
Compiling src/all_reduce.cu                   > /home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/obj/all_reduce.o
Compiling src/broadcast.cu                    > /home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/obj/broadcast.o
Compiling src/reduce.cu                       > /home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/obj/reduce.o
Compiling src/reduce_scatter.cu               > /home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/obj/reduce_scatter.o
Linking   libnccl.so.1.3.4                    > /home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/lib/libnccl.so.1.3.4
Archiving libnccl_static.a                    > /home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/lib/libnccl_static.a

The static library's name is libnccl_static.a.
I try make install to install the library, and get errors:

$ make install
`/home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/lib/libnccl.so' -> `/usr/local/lib/libnccl.so'
cp: cannot create symbolic link `/usr/local/lib/libnccl.so': Permission denied
`/home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/lib/libnccl.so.1' -> `/usr/local/lib/libnccl.so.1'
cp: cannot create symbolic link `/usr/local/lib/libnccl.so.1': Permission denied
`/home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/lib/libnccl.so.1.3.4' -> `/usr/local/lib/libnccl.so.1.3.4'
cp: cannot create regular file `/usr/local/lib/libnccl.so.1.3.4': Permission denied
`/home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/lib/libnccl_static.a' -> `/usr/local/lib/libnccl_static.a'
cp: cannot create regular file `/usr/local/lib/libnccl_static.a': Permission denied
make: *** [install] Error 1

We need to specify the install directory as make install PREFIX=install:

$ make install PREFIX=install
`/home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/lib/libnccl.so' -> `install/lib/libnccl.so'
`/home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/lib/libnccl.so.1' -> `install/lib/libnccl.so.1'
`/home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/lib/libnccl.so.1.3.4' -> `install/lib/libnccl.so.1.3.4'
`/home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/lib/libnccl_static.a' -> `install/lib/libnccl_static.a'
`/home/liuyiqun01/github/Paddle/build_paddle/third_party/nccl/src/extern_nccl/build/include/nccl.h' -> `install/include/nccl.h'

[luotao1]

LGTM

[luotao1]

这里为什么一定需要cuda 8.0呢？

[Xreki]

因为nccl的Makefile里面设定了NVCC_GENCODE变量，-gencode=arch=compute_60,code=sm_60以上在cuda 8.0才支持。

https://github.com/NVIDIA/nccl/blob/master/Makefile#L20-L25

不过，NVCC_GENCODE这个变量应该也可以在make传进去，比如：

set(NVCC_GENCODE -gencode=arch=compute_35,code=sm_35
                 -gencode=arch=compute_50,code=sm_50 
                 -gencode=arch=compute_52,code=sm_52)
set(NCCL_BUILD_COMMAND "make NVCC_GENCODE=${NVCC_GENCODE}")