[Retiarii] Policy-based RL Strategy

dependencies/recommended.txt

@@ -10,3 +10,5 @@ pytorch-lightning >= 1.1.1, < 1.2
 onnx
 peewee
 graphviz
+gym
+tianshou >= 0.4.1

dependencies/recommended_legacy.txt

@@ -11,3 +11,5 @@ keras == 2.1.6
 onnx
 peewee
 graphviz
+gym
+tianshou >= 0.4.1

docs/requirements.txt

@@ -22,5 +22,7 @@ prettytable
 psutil
 ruamel.yaml
 ipython
+gym
+tianshou
 https://download.pytorch.org/whl/cpu/torch-1.7.1%2Bcpu-cp37-cp37m-linux_x86_64.whl
 https://download.pytorch.org/whl/cpu/torchvision-0.8.2%2Bcpu-cp37-cp37m-linux_x86_64.whl

nni/retiarii/strategy/__init__.py

@@ -6,3 +6,4 @@
 from .evolution import RegularizedEvolution
 from .tpe_strategy import TPEStrategy
 from .local_debug_strategy import _LocalDebugStrategy
+from .rl import PolicyBasedRL

nni/retiarii/strategy/_rl_impl.py

@@ -0,0 +1,121 @@
+# This file might cause import error for those who didn't install RL-related dependencies
+
+import logging
+
+import gym
+import numpy as np
+import torch
+import torch.nn as nn
+
+from gym import spaces
+from tianshou.data import to_torch
+
+from .utils import get_targeted_model
+from ..graph import ModelStatus
+from ..execution import submit_models, wait_models
+
+
+_logger = logging.getLogger(__name__)
+
+
+class ModelEvaluationEnv(gym.Env):
+    def __init__(self, base_model, mutators, search_space):
+        self.base_model = base_model
+        self.mutators = mutators
+        self.search_space = search_space
+        self.ss_keys = list(self.search_space.keys())
+        self.action_dim = max(map(lambda v: len(v), self.search_space.values()))
+        self.num_steps = len(self.search_space)
+
+    @property
+    def observation_space(self):
+        return spaces.Dict({
+            'action_history': spaces.MultiDiscrete([self.action_dim] * self.num_steps),
+            'cur_step': spaces.Discrete(self.num_steps + 1),
+            'action_dim': spaces.Discrete(self.action_dim + 1)
+        })
+
+    @property
+    def action_space(self):
+        return spaces.Discrete(self.action_dim)
+
+    def reset(self):
+        self.action_history = np.zeros(self.num_steps, dtype=np.int32)
+        self.cur_step = 0
+        self.sample = {}
+        return {
+            'action_history': self.action_history,
+            'cur_step': self.cur_step,
+            'action_dim': len(self.search_space[self.ss_keys[self.cur_step]])
+        }
+
+    def step(self, action):
+        cur_key = self.ss_keys[self.cur_step]
+        assert action < len(self.search_space[cur_key]), \
+            f'Current action {action} out of range {self.search_space[cur_key]}.'
+        self.action_history[self.cur_step] = action
+        self.sample[cur_key] = self.search_space[cur_key][action]
+        self.cur_step += 1
+        obs = {
+            'action_history': self.action_history,
+            'cur_step': self.cur_step,
+            'action_dim': len(self.search_space[self.ss_keys[self.cur_step]]) \
+                if self.cur_step < self.num_steps else self.action_dim
+        }
+        if self.cur_step == self.num_steps:
+            model = get_targeted_model(self.base_model, self.mutators, self.sample)
+            _logger.info(f'New model created: {self.sample}')
+            submit_models(model)
+            wait_models(model)
+            if model.status == ModelStatus.Failed:
+                return self.reset(), 0., False, {}
+            rew = model.metric
+            _logger.info(f'Model metric received as reward: {rew}')
+            return obs, rew, True, {}
+        else:
+
+            return obs, 0., False, {}
+
+
+class Preprocessor(nn.Module):
+    def __init__(self, obs_space, hidden_dim=64, num_layers=1):
+        super().__init__()
+        self.action_dim = obs_space['action_history'].nvec[0]
+        self.hidden_dim = hidden_dim
+        # first token is [SOS]
+        self.embedding = nn.Embedding(self.action_dim + 1, hidden_dim)
+        self.rnn = nn.LSTM(hidden_dim, hidden_dim, num_layers, batch_first=True)
+
+    def forward(self, obs):
+        seq = nn.functional.pad(obs['action_history'] + 1, (1, 1))  # pad the start token and end token
+        # end token is used to avoid out-of-range of v_s_. Will not actually affect BP.
+        seq = self.embedding(seq.long())
+        feature, _ = self.rnn(seq)
+        return feature[torch.arange(len(feature), device=feature.device), obs['cur_step'].long() + 1]
+
+
+class Actor(nn.Module):
+    def __init__(self, action_space, preprocess):
+        super().__init__()
+        self.preprocess = preprocess
+        self.action_dim = action_space.n
+        self.linear = nn.Linear(self.preprocess.hidden_dim, self.action_dim)
+
+    def forward(self, obs, **kwargs):
+        obs = to_torch(obs, device=self.linear.weight.device)
+        out = self.linear(self.preprocess(obs))
+        # to take care of choices with different number of options
+        mask = torch.arange(self.action_dim).expand(len(out), self.action_dim) >= obs['action_dim'].unsqueeze(1)
+        out[mask.to(out.device)] = float('-inf')
+        return nn.functional.softmax(out), kwargs.get('state', None)
+
+
+class Critic(nn.Module):
+    def __init__(self, preprocess):
+        super().__init__()
+        self.preprocess = preprocess
+        self.linear = nn.Linear(self.preprocess.hidden_dim, 1)
+
+    def forward(self, obs, **kwargs):
+        obs = to_torch(obs, device=self.linear.weight.device)
+        return self.linear(self.preprocess(obs)).squeeze(-1)

nni/retiarii/strategy/rl.py

@@ -0,0 +1,92 @@
+import logging
+from typing import Optional, Callable
+
+from .base import BaseStrategy
+from .utils import dry_run_for_search_space
+from ..execution import query_available_resources
+
+try:
+    has_tianshou = True
+    import torch
+    from tianshou.data import AsyncCollector, Collector, VectorReplayBuffer
+    from tianshou.env import SubprocVectorEnv
+    from tianshou.policy import BasePolicy, PPOPolicy  # pylint: disable=unused-import
+    from ._rl_impl import ModelEvaluationEnv, Preprocessor, Actor, Critic
+except ImportError:
+    has_tianshou = False
+
+
+_logger = logging.getLogger(__name__)
+
+
+class PolicyBasedRL(BaseStrategy):
+    """
+    Algorithm for policy-based reinforcement learning.
+    This is a wrapper of algorithms provided in tianshou (PPO by default),
+    and can be easily customized with other algorithms that inherit ``BasePolicy`` (e.g., REINFORCE [1]_).
+
+    Note that RL algorithms are known to have issues on Windows and MacOS. They will be supported in future.
+
+    Parameters
+    ----------
+    max_collect : int
+        How many times collector runs to collect trials for RL. Default 100.
+    trial_per_collect : int
+        How many trials (trajectories) each time collector collects.
+        After each collect, trainer will sample batch from replay buffer and do the update. Default: 20.
+    policy_fn : function
+        Takes ``ModelEvaluationEnv`` as input and return a policy. See ``_default_policy_fn`` for an example.
+    asynchronous : bool
+        If true, in each step, collector won't wait for all the envs to complete.
+        This should generally not affect the result, but might affect the efficiency. Note that a slightly more trials
+        than expected might be collected if this is enabled.
+        If asynchronous is false, collector will wait for all parallel environments to complete in each step.
+        See ``tianshou.data.AsyncCollector`` for more details.
+
+    References
+    ----------
+
+    .. [1] Barret Zoph and Quoc V. Le, "Neural Architecture Search with Reinforcement Learning".
+        https://arxiv.org/abs/1611.01578
+    """
+
+    def __init__(self, max_collect: int = 100, trial_per_collect = 20,
+                 policy_fn: Optional[Callable[['ModelEvaluationEnv'], 'BasePolicy']] = None, asynchronous: bool = True):
+        if not has_tianshou:
+            raise ImportError('`tianshou` is required to run RL-based strategy. '
+                              'Please use "pip install tianshou" to install it beforehand.')
+
+        self.policy_fn = policy_fn or self._default_policy_fn
+        self.max_collect = max_collect
+        self.trial_per_collect = trial_per_collect
+        self.asynchronous = asynchronous
+
+    @staticmethod
+    def _default_policy_fn(env):
+        net = Preprocessor(env.observation_space)
+        actor = Actor(env.action_space, net)
+        critic = Critic(net)
+        optim = torch.optim.Adam(set(actor.parameters()).union(critic.parameters()), lr=1e-4)
+        return PPOPolicy(actor, critic, optim, torch.distributions.Categorical,
+                         discount_factor=1., action_space=env.action_space)
+
+    def run(self, base_model, applied_mutators):
+        search_space = dry_run_for_search_space(base_model, applied_mutators)
+        concurrency = query_available_resources()
+
+        env_fn = lambda: ModelEvaluationEnv(base_model, applied_mutators, search_space)
+        policy = self.policy_fn(env_fn())
+
+        if self.asynchronous:
+            # wait for half of the env complete in each step
+            env = SubprocVectorEnv([env_fn for _ in range(concurrency)], wait_num=int(concurrency * 0.5))
+            collector = AsyncCollector(policy, env, VectorReplayBuffer(20000, len(env)))
+        else:
+            env = SubprocVectorEnv([env_fn for _ in range(concurrency)])
+            collector = Collector(policy, env, VectorReplayBuffer(20000, len(env)))
+
+        for cur_collect in range(1, self.max_collect + 1):
+            _logger.info('Collect [%d] Running...', cur_collect)
+            result = collector.collect(n_episode=self.trial_per_collect)
+            _logger.info('Collect [%d] Result: %s', cur_collect, str(result))
+            policy.update(0, collector.buffer, batch_size=64, repeat=5)

pipelines/full-test-linux.yml

@@ -35,6 +35,7 @@ jobs:
       python3 -m pip install keras==2.1.6
       python3 -m pip install tensorflow==2.3.1 tensorflow-estimator==2.3.0
       python3 -m pip install thop
+      python3 -m pip install tianshou>=0.4.1 gym
       sudo apt-get install swig -y
     displayName: Install extra dependencies
 

pipelines/full-test-windows.yml

@@ -30,6 +30,7 @@ jobs:
       python -m pip install torch==1.6.0 torchvision==0.7.0 -f https://download.pytorch.org/whl/torch_stable.html
       python -m pip install 'pytorch-lightning>=1.1.1,<1.2'
       python -m pip install tensorflow==2.3.1 tensorflow-estimator==2.3.0
+      python -m pip install tianshou>=0.4.1 gym
     displayName: Install extra dependencies
 
   # Need del later

test/ut/retiarii/test_strategy.py

@@ -1,11 +1,13 @@
 import random
+import sys
 import time
 import threading
 from typing import *
 
 import nni.retiarii.execution.api
 import nni.retiarii.nn.pytorch as nn
 import nni.retiarii.strategy as strategy
+import pytest
 import torch
 import torch.nn.functional as F
 from nni.retiarii import Model
@@ -58,7 +60,7 @@ def _reset_execution_engine(engine=None):
 
 
 class Net(nn.Module):
-    def __init__(self, hidden_size=32):
+    def __init__(self, hidden_size=32, diff_size=False):
         super(Net, self).__init__()
         self.conv1 = nn.Conv2d(1, 20, 5, 1)
         self.conv2 = nn.Conv2d(20, 50, 5, 1)
@@ -69,7 +71,7 @@ def __init__(self, hidden_size=32):
         self.fc2 = nn.LayerChoice([
             nn.Linear(hidden_size, 10, bias=False),
             nn.Linear(hidden_size, 10, bias=True)
-        ], label='fc2')
+        ] + ([] if not diff_size else [nn.Linear(hidden_size, 10, bias=False)]), label='fc2')
 
     def forward(self, x):
         x = F.relu(self.conv1(x))
@@ -82,8 +84,8 @@ def forward(self, x):
         return F.log_softmax(x, dim=1)
 
 
-def _get_model_and_mutators():
-    base_model = Net()
+def _get_model_and_mutators(**kwargs):
+    base_model = Net(**kwargs)
     script_module = torch.jit.script(base_model)
     base_model_ir = convert_to_graph(script_module, base_model)
     base_model_ir.evaluator = DebugEvaluator()
@@ -139,7 +141,25 @@ def test_evolution():
     _reset_execution_engine()
 
 
+@pytest.mark.skipif(sys.platform in ('win32', 'darwin'), reason='Does not run on Windows and MacOS')
+def test_rl():
+    rl = strategy.PolicyBasedRL(max_collect=2, trial_per_collect=10)
+    engine = MockExecutionEngine(failure_prob=0.2)
+    _reset_execution_engine(engine)
+    rl.run(*_get_model_and_mutators(diff_size=True))
+    wait_models(*engine.models)
+    _reset_execution_engine()
+
+    rl = strategy.PolicyBasedRL(max_collect=2, trial_per_collect=10, asynchronous=False)
+    engine = MockExecutionEngine(failure_prob=0.2)
+    _reset_execution_engine(engine)
+    rl.run(*_get_model_and_mutators())
+    wait_models(*engine.models)
+    _reset_execution_engine()
+
+
 if __name__ == '__main__':
     test_grid_search()
     test_random_search()
     test_evolution()
+    test_rl()