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listen_and_serv_op support async update #10042

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jacquesqiao
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@jacquesqiao jacquesqiao commented Apr 19, 2018

fix: #9997

…qiao/Paddle into add-async-listen-and-serv-op
…qiao/Paddle into add-async-listen-and-serv-op
…om/jacquesqiao/Paddle into add-async-listen-and-serv-op
…om/jacquesqiao/Paddle into add-async-listen-and-serv-op
…om/jacquesqiao/Paddle into add-async-listen-and-serv-op
@jacquesqiao jacquesqiao changed the title [WIP] listen_and_serv_op support async update listen_and_serv_op support async update Apr 24, 2018
std::unordered_map<std::string, int32_t> grad_to_id;
std::unordered_map<int32_t, std::string> id_to_grad;

auto grad_to_id_str = Attr<std::vector<std::string>>("grad_to_id");
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grad_to_id_str can be generated by listen_and_serv_op when initializing, read the ProgramDesc blocks and create a mapping, so we can save this attribute.

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I think grad_to_id_str should be created in Python by transpiler because the transpile logic know how to split the operator and block, listen_and_serv_op just use the result is fine, or it has to understand the detailed logic of transpiler.

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Firstly we want to make listen_and_serv_op general, that means it should not know that attributes and inputs are "grads" or parameters, it should simply receive the data and run a block.

In that case, for Async Execution, listen_and_serv is responsible to determine which block need to run when the data arrives. Just open for discussion.

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After discussing with @typhoonzero, I get the point, I totally agree with the idea that listen_and_serv_op should be a general operator! We will find a better way to implement async update in the future PRs.

@@ -30,9 +30,13 @@ enum CallStatus { PROCESS = 0, FINISH };
class RequestBase {
public:
explicit RequestBase(GrpcService::AsyncService* service,
::grpc::ServerCompletionQueue* cq,
::grpc::ServerCompletionQueue* cq, bool sync_mode,
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maybe is_sync or just sync can tell the meaning?

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I think sync_mode means it works in a mode, but is_sync means itself is async. So I think sync_mode is better.

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I see.

auto optimize_prepared = executor->Prepare(*program, block_list);
std::unordered_map<std::string,
std::shared_ptr<framework::ExecutorPrepareContext>>
grad_to_prepared;
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grad_to_prepared_block

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done

LOG(ERROR) << "run sub program error " << e.what();
}
});
// TODO(qiao) maybe we can remove this
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removing this means more "async" mode, trainer even doesn't know whether the sent gradient is updated to the server side weights before it gets the latest weights. Or do you mean by letting updates to different weights become parallel?

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The current implementation will update gradients in sequence if we keep this wait. This may influence the effect, I will do some test on it.

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After discussing with @typhoonzero , we think that each gradient should be put to an independent block queue to ensure that they are updated without conflict.

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we think that each gradient should be put to an independent block queue

Do you mean each gradient of one parameter, such as grad_w1(trainer0), grad_w1(trainer1), grad_w2(trainer0), we put grad_w1(trainer0) and grad_w1(trainer1) into a queue, and grad_w2(trainer0) into another one?

According to the design doc, maybe we need multiple BlockingQueues so that each parameter can own one of them to implement a lock of updating parameter.

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yes, we need multiple block queue, each will store gradients for on parameters, but we do not need to add a lock, because the queue will block until the optimize block is finished.

queue_(queue),
responder_(&ctx_) {
if (sync_mode_) {
request_.reset(new VariableResponse(scope, dev_ctx_, false));
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request_.reset(new VariableResponse(
scope,
dev_ctx_,
!sync_mode_ // create_scope
));

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I thought a while here, and think the current code is easier for user understand the intent.

@@ -61,7 +63,7 @@ class VariableResponse {
// other: number of error field.
int Parse(const ::grpc::ByteBuffer& byte_buffer);

const framework::Scope& GetLocalScope() const { return *local_scope_; }
framework::Scope& GetLocalScope() const { return *local_scope_; }
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Consider GetMutableLocalScope that returns a pointer and avoid removing the const?

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done

@@ -221,6 +327,12 @@ from send_op and send back variables to recv_op.
"IP address to listen on.")
.SetDefault("127.0.0.1:6164")
.AddCustomChecker([](const std::string &ip) { return !ip.empty(); });
AddAttr<std::vector<std::string>>(
"grad_to_id",
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grad_to_block_id?

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done

@@ -143,7 +143,8 @@ def transpile(self,
program=None,
pservers="127.0.0.1:6174",
trainers=1,
split_method=splitter.round_robin):
split_method=splitter.round_robin,
sync_mode=True):
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need comment

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done

AsyncExecuteBlock(executor, grad_to_prepared_block[recv_var_name].get(),
v.second->GetMutableLocalScope());
// TODO(qiao): explain why
if (var->IsType<framework::SelectedRows>()) {
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Maybe we don't need to clear the rows, because of each gradient var is in a new scope.

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Great suggestion! removed.

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It LGTM now, does python wrapping in io.py need to be updated in this PR or later?

@jacquesqiao
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@typhoonzero the CI is too slow, I will give another PR to fix the io.py.

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LGTM++

@jacquesqiao jacquesqiao merged commit 6d93456 into PaddlePaddle:develop Apr 26, 2018
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listen_and_serv_op support async update
4 participants