master

zeus.run.master

Defines the ZeusMaster class, which drives batch size optimization and training.

ZeusMaster

Drives Zeus across multiple recurrences of a job.

The main purpose of ZeusMaster is to launch training scripts integrated with ZeusDataLoader, controlling it by setting environment variables. For the environment variables, see the run_job method as well as ZeusDataLoader's class docstring.

The optimal batch size is searched for and exploited using the BatchSizeOptimizer object passed in through the constructor.

Source code in zeus/run/master.py

class ZeusMaster:
    """Drives Zeus across multiple recurrences of a job.

    The main purpose of `ZeusMaster` is to launch training scripts integrated
    with [`ZeusDataLoader`][zeus.run.ZeusDataLoader], controlling it by setting
    environment variables. For the environment variables, see the
    [`run_job`][zeus.run.ZeusMaster.run_job] method as well as
    [`ZeusDataLoader`][zeus.run.ZeusDataLoader]'s class docstring.

    The optimal batch size is searched for and exploited using the
    [`BatchSizeOptimizer`][zeus.policy.BatchSizeOptimizer] object passed in
    through the constructor.
    """

    def __init__(
        self,
        batch_size_optimizer: BatchSizeOptimizer,
        log_base: str,
        monitor_path: str,
        seed: int = 123456,
        observer_mode: bool = False,
        profile_warmup_iters: int = 10,
        profile_measure_iters: int = 40,
    ) -> None:
        """Initialize the master.

        Args:
            batch_size_optimizer: The user is expected to construct the
                [`BatchSizeOptimizer`][zeus.policy.BatchSizeOptimizer] with the desired
                policy and pass it into the master class.
            log_base: Absolute path where logs will be stored. A separate directory
                will be created inside, whose name is determined by the job and current time.
            monitor_path: Absolute path to the power monitor binary.
            seed: The random seed. Every invocation of the [`run`][zeus.run.ZeusMaster.run]
                method in this class is deterministic given the random seed, because the
                internal RNG states are deepcopied before servicing jobs.
            observer_mode: When Observer Mode is on, the maximum power limit is
                always used instead of the optimal power limit. However, internal time and
                energy accounting will be done as if the cost-optimal power limit is used.
            profile_warmup_iters: Number of iterations to warm up on a specific power limit.
                This is passed to the [`ZeusDataLoader`][zeus.run.ZeusDataLoader].
            profile_measure_iters: Number of iterations to measure on a specific power limit.
                This is passed to the [`ZeusDataLoader`][zeus.run.ZeusDataLoader].

        """
        # Knob optimizers.
        self.bso = batch_size_optimizer

        # Check if monitor_path is absolute.
        # This is needed since we may change the cwd based on the job's workdir.
        if not Path(monitor_path).is_absolute():
            raise ValueError("monitor_path must be specified as an absolute path.")

        # Log base directory.
        # Needs to be absolute because the training job script may have a different
        # current working directory (when job.workdir is not None).
        if not Path(log_base).is_absolute():
            raise ValueError("log_base must be specified as an absolute path.")
        os.makedirs(log_base, exist_ok=True)
        self.log_base = log_base

        # Save arguments.
        self.seed = seed
        self.monitor_path = monitor_path
        self.observer_mode = observer_mode
        self.profile_warmup_iters = profile_warmup_iters
        self.profile_measure_iters = profile_measure_iters

        # Query the max power limit of the GPU.
        gpus = get_gpus(ensure_homogeneous=True)
        minmax = gpus.getPowerManagementLimitConstraints(0)  # unit: mW
        self.max_pl = minmax[1] // 1000  # unit: W
        print(f"[Zeus Master] Max power limit of {gpus.getName(0)}: {self.max_pl}W")

    def build_logdir(
        self,
        job: Job,
        num_recurrence: int,
        eta_knob: float,
        beta_knob: float,
        exist_ok: bool = True,
    ) -> str:
        r"""Build the `ZEUS_LOG_DIR` string and create the directory.

        Args:
            job: Job to run.
            num_recurrence: The total number of recurrences.
            eta_knob: $\eta$ used in the cost metric.
                $\textrm{cost} = \eta \cdot \textrm{ETA} + (1 - \eta) \cdot \textrm{MaxPower} \cdot \textrm{TTA}$
            beta_knob: `beta_knob * min_cost` is the early stopping cost threshold.
                Set to `np.inf` to disable early stopping.
            exist_ok: Passed to `os.makedirs`. If `False`, will err if the directory
                already exists.
        """
        now = strftime("%Y%m%d%H%M%s", localtime())
        logdir = (
            job.to_logdir() + f"+x{num_recurrence}+eta{eta_knob}+beta{beta_knob}+{now}"
        )
        logdir = f"{self.log_base}/{logdir}"
        os.makedirs(logdir, exist_ok=exist_ok)
        return logdir

    def run_job(
        self,
        job: Job,
        batch_size: int,
        learning_rate: float,
        seed: int,
        logdir: str,
        rec_i: int,
        tries: int,
        eta_knob: float,
        cost_ub: float,
    ) -> tuple[float, float, bool]:
        r"""Launch the training job.

        Args:
            job: The job to run.
            batch_size: The batch size to use.
            learning_rate: The learning rate to use, scaled based on `batch_size`.
            seed: The random seed to use for training.
            logdir: Directory to store log files in.
            rec_i: Recurrence number of this run of the job.
            tries: Retry number of this recurrence of the job.
            eta_knob: $\eta$ used in the cost metric.
                $\textrm{cost} = \eta \cdot \textrm{ETA} + (1 - \eta) \cdot \textrm{MaxPower} \cdot \textrm{TTA}$
            cost_ub: Cost upper bound. The job is terminated when the next epoch is going
                to exceed the cost upper bound.

        Returns:
            A tuple of energy consumption, time consumption, and whether the job reached the target metric.
        """
        # Generate job command
        command = job.gen_command(batch_size, learning_rate, seed, rec_i)

        # Set environment variables
        job_id = f"rec{rec_i:02d}+try{tries:02d}"
        zeus_env = dict(
            ZEUS_LOG_DIR=logdir,
            ZEUS_JOB_ID=job_id,
            ZEUS_COST_THRESH="inf" if cost_ub == np.inf else str(cost_ub),
            ZEUS_ETA_KNOB=str(eta_knob),
            ZEUS_TARGET_METRIC=str(job.target_metric),
            ZEUS_MONITOR_PATH=self.monitor_path,
            ZEUS_PROFILE_PARAMS=f"{self.profile_warmup_iters},{self.profile_measure_iters}",
            ZEUS_USE_OPTIMAL_PL=str(not self.observer_mode),
        )
        env = deepcopy(os.environ)
        env.update(zeus_env)

        # Training script output captured by the master.
        job_output = f"{logdir}/{job_id}.train.log"

        # Training stats (energy, time, reached, end_epoch) written by ZeusDataLoader.
        # This file being found means that the training job is done.
        train_json = Path(f"{logdir}/{job_id}+bs{batch_size}.train.json")

        # Reporting
        print(f"[run job] Launching job with BS {batch_size}:")
        print(f"[run job] {zeus_env=}")
        if job.workdir is not None:
            print(f"[run job] cwd={job.workdir}")
        print(f"[run job] {command=}")
        print(f"[run job] {cost_ub=}")
        print(f"[run job] Job output logged to '{job_output}'")

        # Run the job.
        with open(job_output, "w") as f:
            # Launch subprocess.
            # stderr is redirected to stdout, and stdout to the job_output file.
            proc = subprocess.Popen(
                command,
                cwd=job.workdir,
                stderr=subprocess.STDOUT,
                stdout=f,
            )

            # Check if training is done.
            with open(job_output, "r") as jobf:
                while proc.poll() is None:
                    print(jobf.read(), end="")
                    sleep(1.0)

                # Print out the rest of the script output.
                f.flush()
                print(jobf.read())

                # Report exitcode.
                exitcode = proc.poll()
                print(f"[run job] Job terminated with exit code {exitcode}.")

            # `train_json` must exist at this point.
            if not train_json.exists():
                raise RuntimeError(f"{train_json} does not exist.")

        # Read `train_json` for the training stats.
        with open(train_json, "r") as f:
            stats = json.load(f)
            print(f"[run job] {stats=}")

        # Casting
        if not isinstance(stats["reached"], bool):
            stats["reached"] = stats["reached"].lower() == "true"

        return float(stats["energy"]), float(stats["time"]), stats["reached"]

    def run(
        self,
        job: Job,
        num_recurrence: int,
        batch_sizes: list[int],
        beta_knob: float,
        eta_knob: float,
    ) -> list[HistoryEntry]:
        r"""Run a job that sequentially recurs without overlap.

        Args:
            job: The job to run.
            num_recurrence: How many times the job recurs.
            batch_sizes: List of feasible batch sizes.
            beta_knob: `beta_knob * min_eta` is the early stopping cost threshold.
                Set to `np.inf` to disable early stopping.
            eta_knob: $\eta$ used in the cost metric.
                $\textrm{cost} = \eta \cdot \textrm{ETA} + (1 - \eta) \cdot \textrm{MaxPower} \cdot \textrm{TTA}$

        Returns:
            A list of [`HistoryEntry`][zeus.analyze.HistoryEntry] objects for each job run.
        """
        # Sanity checks
        if job.default_bs is None:
            raise ValueError("You must provide a default batch size for the job.")
        if job.command is None:
            raise ValueError("You must provide a command format string for the job.")
        if eta_knob < 0.0 or eta_knob > 1.0:
            raise ValueError("eta_knob must be in [0.0, 1.0].")

        print(f"[Zeus Master] {job} x {num_recurrence}")
        print(f"[Zeus Master] Batch sizes: {batch_sizes}")

        # Copy all internal state so that simulation does not modify any
        # internal state and is deterministic w.r.t. the random seed.
        bso = deepcopy(self.bso)
        seed = self.seed

        # ZEUS_LOG_DIR: Where all the logs and files are stored for this run.
        logdir = self.build_logdir(job, num_recurrence, eta_knob, beta_knob)

        # Job history list to return.
        history: list[HistoryEntry] = []

        # Save job history to this file, continuously.
        history_file = f"{logdir}/history.py"

        # beta_knob * min_cost is the early stopping cost threshold.
        min_cost = np.inf

        # Register the job in the BSO.
        bso.register_job(job, batch_sizes)

        # Job recurs.
        for rec_i in range(1, num_recurrence + 1):
            print(f"\n[Zeus Master] Recurrence: {rec_i}")

            # The retrying loop. Retry until convergence.
            cost_acc = 0.0
            for tries in range(1, 21):
                # Fetch the knobs to use.
                bs = bso.predict(job)

                # Scale the learning rate.
                lr = job.scale_lr(bs)

                # Launch the job.
                # Power profiling and optimization is done entirely by the ZeusDataLoader.
                # Early stops based on cost_ub.
                energy, time, reached = self.run_job(
                    job=job,
                    batch_size=bs,
                    learning_rate=lr,
                    seed=seed,
                    logdir=logdir,
                    rec_i=rec_i,
                    tries=tries,
                    eta_knob=eta_knob,
                    cost_ub=beta_knob * min_cost,
                )

                # The random seed will be unique for each run, but still jobs will be
                # deterministic w.r.t. each call to `run`.
                seed += 1

                # Compute the cost of this try.
                num_gpus = torch.cuda.device_count()
                cost = zeus_cost(energy, time, eta_knob, self.max_pl * num_gpus)
                print(f"[Zeus Master] {cost=}")

                # Accumulate the cost to track the total cost of this recurrence.
                cost_acc += cost

                # Provide feedback to the BSO.
                bso.observe(job, bs, cost, reached)

                # Record history for visualization.
                history.append(HistoryEntry(bs, None, energy, reached, time))
                with open(history_file, "w") as f:
                    # Intended use:
                    #
                    # ```python
                    # from zeus.analyze import HistoryEntry
                    # history = eval(open(history_file).read())
                    # ```
                    f.write(pprint.pformat(history) + "\n")

                # Reached the target metric. Go to next recurrence.
                if reached:
                    print(
                        "\n[Zeus Master] Reached target metric in "
                        f"{tries} {'try' if tries == 1 else 'tries'}."
                    )
                    # Track the minimum cost.
                    if min_cost > cost_acc:
                        print(
                            f"\n[Zeus Master] Minimum cost updated from {min_cost} to {cost_acc}."
                        )
                        min_cost = cost_acc
                    break
                # Didn't reach the target metric.
                # We assume that the default BS (set by the user) will converge.
                if rec_i == 1:
                    raise RuntimeError(
                        f"The default batch size {job.default_bs} did not converge."
                    )
            else:
                print(
                    "\n[Zeus Master] Job did not reach the target metric in 20 trials!"
                )
                raise RuntimeError("Unreachable target metric.")

        print(f"[Zeus Master]\n{history}")

        return history

__init__

__init__(
    batch_size_optimizer,
    log_base,
    monitor_path,
    seed=123456,
    observer_mode=False,
    profile_warmup_iters=10,
    profile_measure_iters=40,
)

Parameters:

Name	Type	Description	Default
batch_size_optimizer	BatchSizeOptimizer	The user is expected to construct the BatchSizeOptimizer with the desired policy and pass it into the master class.	required
log_base	str	Absolute path where logs will be stored. A separate directory will be created inside, whose name is determined by the job and current time.	required
monitor_path	str	Absolute path to the power monitor binary.	required
seed	int	The random seed. Every invocation of the run method in this class is deterministic given the random seed, because the internal RNG states are deepcopied before servicing jobs.	123456
observer_mode	bool	When Observer Mode is on, the maximum power limit is always used instead of the optimal power limit. However, internal time and energy accounting will be done as if the cost-optimal power limit is used.	False
profile_warmup_iters	int	Number of iterations to warm up on a specific power limit. This is passed to the ZeusDataLoader.	10
profile_measure_iters	int	Number of iterations to measure on a specific power limit. This is passed to the ZeusDataLoader.	40

Source code in zeus/run/master.py

def __init__(
    self,
    batch_size_optimizer: BatchSizeOptimizer,
    log_base: str,
    monitor_path: str,
    seed: int = 123456,
    observer_mode: bool = False,
    profile_warmup_iters: int = 10,
    profile_measure_iters: int = 40,
) -> None:
    """Initialize the master.

    Args:
        batch_size_optimizer: The user is expected to construct the
            [`BatchSizeOptimizer`][zeus.policy.BatchSizeOptimizer] with the desired
            policy and pass it into the master class.
        log_base: Absolute path where logs will be stored. A separate directory
            will be created inside, whose name is determined by the job and current time.
        monitor_path: Absolute path to the power monitor binary.
        seed: The random seed. Every invocation of the [`run`][zeus.run.ZeusMaster.run]
            method in this class is deterministic given the random seed, because the
            internal RNG states are deepcopied before servicing jobs.
        observer_mode: When Observer Mode is on, the maximum power limit is
            always used instead of the optimal power limit. However, internal time and
            energy accounting will be done as if the cost-optimal power limit is used.
        profile_warmup_iters: Number of iterations to warm up on a specific power limit.
            This is passed to the [`ZeusDataLoader`][zeus.run.ZeusDataLoader].
        profile_measure_iters: Number of iterations to measure on a specific power limit.
            This is passed to the [`ZeusDataLoader`][zeus.run.ZeusDataLoader].

    """
    # Knob optimizers.
    self.bso = batch_size_optimizer

    # Check if monitor_path is absolute.
    # This is needed since we may change the cwd based on the job's workdir.
    if not Path(monitor_path).is_absolute():
        raise ValueError("monitor_path must be specified as an absolute path.")

    # Log base directory.
    # Needs to be absolute because the training job script may have a different
    # current working directory (when job.workdir is not None).
    if not Path(log_base).is_absolute():
        raise ValueError("log_base must be specified as an absolute path.")
    os.makedirs(log_base, exist_ok=True)
    self.log_base = log_base

    # Save arguments.
    self.seed = seed
    self.monitor_path = monitor_path
    self.observer_mode = observer_mode
    self.profile_warmup_iters = profile_warmup_iters
    self.profile_measure_iters = profile_measure_iters

    # Query the max power limit of the GPU.
    gpus = get_gpus(ensure_homogeneous=True)
    minmax = gpus.getPowerManagementLimitConstraints(0)  # unit: mW
    self.max_pl = minmax[1] // 1000  # unit: W
    print(f"[Zeus Master] Max power limit of {gpus.getName(0)}: {self.max_pl}W")

build_logdir

build_logdir(
    job, num_recurrence, eta_knob, beta_knob, exist_ok=True
)

Build the ZEUS_LOG_DIR string and create the directory.

Parameters:

Name	Type	Description	Default
job	Job	Job to run.	required
num_recurrence	int	The total number of recurrences.	required
eta_knob	float	\(\eta\) used in the cost metric. \(\textrm{cost} = \eta \cdot \textrm{ETA} + (1 - \eta) \cdot \textrm{MaxPower} \cdot \textrm{TTA}\)	required
beta_knob	float	beta_knob * min_cost is the early stopping cost threshold. Set to np.inf to disable early stopping.	required
exist_ok	bool	Passed to os.makedirs. If False, will err if the directory already exists.	True

Source code in zeus/run/master.py

def build_logdir(
    self,
    job: Job,
    num_recurrence: int,
    eta_knob: float,
    beta_knob: float,
    exist_ok: bool = True,
) -> str:
    r"""Build the `ZEUS_LOG_DIR` string and create the directory.

    Args:
        job: Job to run.
        num_recurrence: The total number of recurrences.
        eta_knob: $\eta$ used in the cost metric.
            $\textrm{cost} = \eta \cdot \textrm{ETA} + (1 - \eta) \cdot \textrm{MaxPower} \cdot \textrm{TTA}$
        beta_knob: `beta_knob * min_cost` is the early stopping cost threshold.
            Set to `np.inf` to disable early stopping.
        exist_ok: Passed to `os.makedirs`. If `False`, will err if the directory
            already exists.
    """
    now = strftime("%Y%m%d%H%M%s", localtime())
    logdir = (
        job.to_logdir() + f"+x{num_recurrence}+eta{eta_knob}+beta{beta_knob}+{now}"
    )
    logdir = f"{self.log_base}/{logdir}"
    os.makedirs(logdir, exist_ok=exist_ok)
    return logdir

run_job

run_job(
    job,
    batch_size,
    learning_rate,
    seed,
    logdir,
    rec_i,
    tries,
    eta_knob,
    cost_ub,
)

Launch the training job.

Parameters:

Name	Type	Description	Default
job	Job	The job to run.	required
batch_size	int	The batch size to use.	required
learning_rate	float	The learning rate to use, scaled based on batch_size.	required
seed	int	The random seed to use for training.	required
logdir	str	Directory to store log files in.	required
rec_i	int	Recurrence number of this run of the job.	required
tries	int	Retry number of this recurrence of the job.	required
eta_knob	float	\(\eta\) used in the cost metric. \(\textrm{cost} = \eta \cdot \textrm{ETA} + (1 - \eta) \cdot \textrm{MaxPower} \cdot \textrm{TTA}\)	required
cost_ub	float	Cost upper bound. The job is terminated when the next epoch is going to exceed the cost upper bound.	required

Returns:

Type	Description
tuple[float, float, bool]	A tuple of energy consumption, time consumption, and whether the job reached the target metric.

Source code in zeus/run/master.py

def run_job(
    self,
    job: Job,
    batch_size: int,
    learning_rate: float,
    seed: int,
    logdir: str,
    rec_i: int,
    tries: int,
    eta_knob: float,
    cost_ub: float,
) -> tuple[float, float, bool]:
    r"""Launch the training job.

    Args:
        job: The job to run.
        batch_size: The batch size to use.
        learning_rate: The learning rate to use, scaled based on `batch_size`.
        seed: The random seed to use for training.
        logdir: Directory to store log files in.
        rec_i: Recurrence number of this run of the job.
        tries: Retry number of this recurrence of the job.
        eta_knob: $\eta$ used in the cost metric.
            $\textrm{cost} = \eta \cdot \textrm{ETA} + (1 - \eta) \cdot \textrm{MaxPower} \cdot \textrm{TTA}$
        cost_ub: Cost upper bound. The job is terminated when the next epoch is going
            to exceed the cost upper bound.

    Returns:
        A tuple of energy consumption, time consumption, and whether the job reached the target metric.
    """
    # Generate job command
    command = job.gen_command(batch_size, learning_rate, seed, rec_i)

    # Set environment variables
    job_id = f"rec{rec_i:02d}+try{tries:02d}"
    zeus_env = dict(
        ZEUS_LOG_DIR=logdir,
        ZEUS_JOB_ID=job_id,
        ZEUS_COST_THRESH="inf" if cost_ub == np.inf else str(cost_ub),
        ZEUS_ETA_KNOB=str(eta_knob),
        ZEUS_TARGET_METRIC=str(job.target_metric),
        ZEUS_MONITOR_PATH=self.monitor_path,
        ZEUS_PROFILE_PARAMS=f"{self.profile_warmup_iters},{self.profile_measure_iters}",
        ZEUS_USE_OPTIMAL_PL=str(not self.observer_mode),
    )
    env = deepcopy(os.environ)
    env.update(zeus_env)

    # Training script output captured by the master.
    job_output = f"{logdir}/{job_id}.train.log"

    # Training stats (energy, time, reached, end_epoch) written by ZeusDataLoader.
    # This file being found means that the training job is done.
    train_json = Path(f"{logdir}/{job_id}+bs{batch_size}.train.json")

    # Reporting
    print(f"[run job] Launching job with BS {batch_size}:")
    print(f"[run job] {zeus_env=}")
    if job.workdir is not None:
        print(f"[run job] cwd={job.workdir}")
    print(f"[run job] {command=}")
    print(f"[run job] {cost_ub=}")
    print(f"[run job] Job output logged to '{job_output}'")

    # Run the job.
    with open(job_output, "w") as f:
        # Launch subprocess.
        # stderr is redirected to stdout, and stdout to the job_output file.
        proc = subprocess.Popen(
            command,
            cwd=job.workdir,
            stderr=subprocess.STDOUT,
            stdout=f,
        )

        # Check if training is done.
        with open(job_output, "r") as jobf:
            while proc.poll() is None:
                print(jobf.read(), end="")
                sleep(1.0)

            # Print out the rest of the script output.
            f.flush()
            print(jobf.read())

            # Report exitcode.
            exitcode = proc.poll()
            print(f"[run job] Job terminated with exit code {exitcode}.")

        # `train_json` must exist at this point.
        if not train_json.exists():
            raise RuntimeError(f"{train_json} does not exist.")

    # Read `train_json` for the training stats.
    with open(train_json, "r") as f:
        stats = json.load(f)
        print(f"[run job] {stats=}")

    # Casting
    if not isinstance(stats["reached"], bool):
        stats["reached"] = stats["reached"].lower() == "true"

    return float(stats["energy"]), float(stats["time"]), stats["reached"]

run

run(job, num_recurrence, batch_sizes, beta_knob, eta_knob)

Run a job that sequentially recurs without overlap.

Parameters:

Name	Type	Description	Default
job	Job	The job to run.	required
num_recurrence	int	How many times the job recurs.	required
batch_sizes	list[int]	List of feasible batch sizes.	required
beta_knob	float	beta_knob * min_eta is the early stopping cost threshold. Set to np.inf to disable early stopping.	required
eta_knob	float	\(\eta\) used in the cost metric. \(\textrm{cost} = \eta \cdot \textrm{ETA} + (1 - \eta) \cdot \textrm{MaxPower} \cdot \textrm{TTA}\)	required

Returns:

Type	Description
list[HistoryEntry]	A list of HistoryEntry objects for each job run.

Source code in zeus/run/master.py

def run(
    self,
    job: Job,
    num_recurrence: int,
    batch_sizes: list[int],
    beta_knob: float,
    eta_knob: float,
) -> list[HistoryEntry]:
    r"""Run a job that sequentially recurs without overlap.

    Args:
        job: The job to run.
        num_recurrence: How many times the job recurs.
        batch_sizes: List of feasible batch sizes.
        beta_knob: `beta_knob * min_eta` is the early stopping cost threshold.
            Set to `np.inf` to disable early stopping.
        eta_knob: $\eta$ used in the cost metric.
            $\textrm{cost} = \eta \cdot \textrm{ETA} + (1 - \eta) \cdot \textrm{MaxPower} \cdot \textrm{TTA}$

    Returns:
        A list of [`HistoryEntry`][zeus.analyze.HistoryEntry] objects for each job run.
    """
    # Sanity checks
    if job.default_bs is None:
        raise ValueError("You must provide a default batch size for the job.")
    if job.command is None:
        raise ValueError("You must provide a command format string for the job.")
    if eta_knob < 0.0 or eta_knob > 1.0:
        raise ValueError("eta_knob must be in [0.0, 1.0].")

    print(f"[Zeus Master] {job} x {num_recurrence}")
    print(f"[Zeus Master] Batch sizes: {batch_sizes}")

    # Copy all internal state so that simulation does not modify any
    # internal state and is deterministic w.r.t. the random seed.
    bso = deepcopy(self.bso)
    seed = self.seed

    # ZEUS_LOG_DIR: Where all the logs and files are stored for this run.
    logdir = self.build_logdir(job, num_recurrence, eta_knob, beta_knob)

    # Job history list to return.
    history: list[HistoryEntry] = []

    # Save job history to this file, continuously.
    history_file = f"{logdir}/history.py"

    # beta_knob * min_cost is the early stopping cost threshold.
    min_cost = np.inf

    # Register the job in the BSO.
    bso.register_job(job, batch_sizes)

    # Job recurs.
    for rec_i in range(1, num_recurrence + 1):
        print(f"\n[Zeus Master] Recurrence: {rec_i}")

        # The retrying loop. Retry until convergence.
        cost_acc = 0.0
        for tries in range(1, 21):
            # Fetch the knobs to use.
            bs = bso.predict(job)

            # Scale the learning rate.
            lr = job.scale_lr(bs)

            # Launch the job.
            # Power profiling and optimization is done entirely by the ZeusDataLoader.
            # Early stops based on cost_ub.
            energy, time, reached = self.run_job(
                job=job,
                batch_size=bs,
                learning_rate=lr,
                seed=seed,
                logdir=logdir,
                rec_i=rec_i,
                tries=tries,
                eta_knob=eta_knob,
                cost_ub=beta_knob * min_cost,
            )

            # The random seed will be unique for each run, but still jobs will be
            # deterministic w.r.t. each call to `run`.
            seed += 1

            # Compute the cost of this try.
            num_gpus = torch.cuda.device_count()
            cost = zeus_cost(energy, time, eta_knob, self.max_pl * num_gpus)
            print(f"[Zeus Master] {cost=}")

            # Accumulate the cost to track the total cost of this recurrence.
            cost_acc += cost

            # Provide feedback to the BSO.
            bso.observe(job, bs, cost, reached)

            # Record history for visualization.
            history.append(HistoryEntry(bs, None, energy, reached, time))
            with open(history_file, "w") as f:
                # Intended use:
                #
                # ```python
                # from zeus.analyze import HistoryEntry
                # history = eval(open(history_file).read())
                # ```
                f.write(pprint.pformat(history) + "\n")

            # Reached the target metric. Go to next recurrence.
            if reached:
                print(
                    "\n[Zeus Master] Reached target metric in "
                    f"{tries} {'try' if tries == 1 else 'tries'}."
                )
                # Track the minimum cost.
                if min_cost > cost_acc:
                    print(
                        f"\n[Zeus Master] Minimum cost updated from {min_cost} to {cost_acc}."
                    )
                    min_cost = cost_acc
                break
            # Didn't reach the target metric.
            # We assume that the default BS (set by the user) will converge.
            if rec_i == 1:
                raise RuntimeError(
                    f"The default batch size {job.default_bs} did not converge."
                )
        else:
            print(
                "\n[Zeus Master] Job did not reach the target metric in 20 trials!"
            )
            raise RuntimeError("Unreachable target metric.")

    print(f"[Zeus Master]\n{history}")

    return history