Update FAQ.md

增加GPU环境运行Serving报错，GPU count is: 0的处理方法

doc/FAQ.md

@@ -37,3 +37,25 @@
     client端的日志直接打印到标准输出。
 
     通过在部署服务之前 'export  GLOG_v=3'可以输出更为详细的日志信息。
+    
+- Q: GPU环境运行Serving报错，GPU count is: 0。
+  ```
+  terminate called after throwing an instance of 'paddle::platform::EnforceNotMet'
+  what():
+  --------------------------------------------
+  C++ Call Stacks (More useful to developers):
+  --------------------------------------------
+  0   std::string paddle::platform::GetTraceBackString<std::string const&>(std::string const&, char const*, int)
+  1   paddle::platform::SetDeviceId(int)
+  2   paddle::AnalysisConfig::fraction_of_gpu_memory_for_pool() const
+  3   std::unique_ptr<paddle::PaddlePredictor, std::default_delete<paddle::PaddlePredictor> > paddle::CreatePaddlePredictor<paddle::AnalysisConfig, (paddle::PaddleEngineKind)2>(paddle::AnalysisConfig const&)
+  4   std::unique_ptr<paddle::PaddlePredictor, std::default_delete<paddle::PaddlePredictor> > paddle::CreatePaddlePredictor<paddle::AnalysisConfig>(paddle::AnalysisConfig const&)
+  ----------------------
+  Error Message Summary:
+  ----------------------
+  InvalidArgumentError: Device id must be less than GPU count, but received id is: 0. GPU count is: 0.
+  [Hint: Expected id < GetCUDADeviceCount(), but received id:0 >= GetCUDADeviceCount():0.] at (/home/scmbuild/workspaces_cluster.dev/baidu.lib.paddlepaddle/baidu/lib/paddlepaddle/Paddle/paddle/fluid/platform/gpu_info.cc:211)
+  ```
+  A: libcuda.so没有链接成功。首先在机器上找到libcuda.so，ldd检查libnvidia版本与nvidia-smi中版本一致（libnvidia-fatbinaryloader.so.418.39，与NVIDIA-SMI 418.39 Driver Version: 418.39）,然后用export导出libcuda.so的路径即可（例如libcuda.so在/usr/lib64/，export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/lib64/）
+  
+