提交 a6fbfed2 编写于 作者: Y Yang Yang(Tony) 提交者: GitHub

Update executor.md

上级 3b879598
......@@ -5,8 +5,8 @@
`Executor` evaluates a `ProgramDesc`. Essentially, it instantializes Variables and Operators, then run all the operators
```c++
void Executor::Run(const ProgramDesc& pdesc, Scope* scope) {
auto& block = pdesc.blocks(0);
void Executor::Run(const ProgramDesc& pdesc, Scope* scope, int block_id) {
auto& block = pdesc.blocks(block_id);
auto& device = device_contexts_[0];
// Instantiate all the vars in the global scope
......@@ -14,55 +14,19 @@ void Executor::Run(const ProgramDesc& pdesc, Scope* scope) {
scope->NewVar(var.name());
}
// Decide which operator should be run
std::vector<bool> should_run = Prune(pdesc);
// Run the block
Scope& local_scope = scope->NewScope();
for (size_t i = 0; i < should_run.size(); ++i) {
if (should_run[i]) {
for (auto var : block.ops(i).outputs()) {
for (auto argu : var.arguments()) {
// Create temp variable in the local_scope
if (local_scope.FindVar(argu) == nullptr) {
local_scope.NewVar(argu);
}
for (auto var : block.ops(i).outputs()) {
for (auto argu : var.arguments()) {
// Create temp variable in the local_scope
if (local_scope.FindVar(argu) == nullptr) {
local_scope.NewVar(argu);
}
}
auto op = paddle::framework::OpRegistry::CreateOp(block.ops(i));
op->Run(local_scope, *device);
}
auto op = paddle::framework::OpRegistry::CreateOp(block.ops(i));
op->Run(local_scope, *device);
}
}
```
## Challenge
It is not hard to simply evaluate a graph. However, it is hard to determine which op should be run. Consider the following different situations.
```python
# Case 1: run foward pass.
cost_np = executor.run(target=cost)
# Case 2: run backward passing.
opts_np, _ = executor.run(target=[cost, opt])
# Case 3: run checkpointing
_ = executor.run(target=checkpoint)
```
We want to support the evaluation of both variables and operators.
## Solution
To support evaluation of operators, we add `is_target` field in the `OpDesc`.
```c++
message OpDesc {
required string type = 3;
repeated Var inputs = 1;
repeated Var outputs = 2;
repeated Attr attrs = 4;
required bool is_target = 5 [ default = false ]; // true if the op is target
};
```
To support evaluation of variables, we add [fetch_op](https://github.com/PaddlePaddle/Paddle/pull/4599). For each variable in the `target`, we insert a `fetch_op` into the `ProgramDesc`. (Also, a user may want to overwrite a variable, so we also added [feed_op](https://github.com/PaddlePaddle/Paddle/pull/4599). )
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