Basic double buffer for cpp reader

* fix mac build error

* override GetExpectedKernelType for cast op

* fix typo

* add cuda unittest

Fix sparse update memory error for distributed training

Update getstarted doc

Print exception message from threads

* test cpu float16 data transform

* add isnan etc

* small fix

* fix containsNAN test error

* add data_type transform GPU test

* add float16 GPU example

* fix error

* fix GPU test error

* initial commit

* fix error

* small fix

* add more gemm fp16 tests

* fix error

* add utility function

Move 2 pictures from /v2 to /fluid

fix document deployment

Add guide for documentation-9-"RNN模型"

Fix some outdated links in doc/fluid/read_source.md (#8851)

* Add test for nested RecordEvent.

* Remove the debug information.

* Add log information for the 3 usages and reduce the loop counts of nested case.

Improve the timeline profiler

Fix nccl version in manylinux develop Docker image

Add log before op Run

[Speed] Refine elementwise sub,div,min,max gradient functor

Add capi-noavx-openblas download link

* Add profiling information for inference example, recognize digits.

* Refine the profiling method.

* Correct the use of RecordEvent and simplify recognize_digits.

add timeline profile howto