refactor(slurmd): improve comments and function names. Simplify

try/catch blocks.

Add better support for comma-separated values in `get_slurmd_info`

charms/slurmd/src/charm.py

@@ -334,7 +334,7 @@ def _check_status(self) -> bool:
     def _reboot_if_required(self, now: bool = False) -> None:
         """Perform a reboot of the unit if required, e.g. following a driver installation."""
         if Path("/var/run/reboot-required").exists():
-            logger.info("unit rebooting")
+            logger.info("rebooting unit %s", self.unit.name)
             self.unit.reboot(now)
 
     @staticmethod
@@ -373,34 +373,25 @@ def get_node(self) -> Dict[Any, Any]:
         """Get the node from stored state."""
         slurmd_info = machine.get_slurmd_info()
 
-        # Get GPU info and build GRES configuration.
         gres_info = []
-        if gpus := gpu.get_gpus():
+        if gpus := gpu.get_all_gpu():
             for model, devices in gpus.items():
                 # Build gres.conf line for this GPU model.
                 if len(devices) == 1:
                     device_suffix = next(iter(devices))
                 else:
-                    # For multi-gpu setups, "File" uses ranges and strides syntax,
-                    # e.g. File=/dev/nvidia[0-3], File=/dev/nvidia[0,2-3]
+                    # Get numeric range of devices associated with this GRES resource. See:
+                    # https://slurm.schedmd.com/gres.conf.html#OPT_File
                     device_suffix = self._ranges_and_strides(sorted(devices))
                 gres_line = {
-                    # NodeName included in node_parameters.
                     "Name": "gpu",
                     "Type": model,
                     "File": f"/dev/nvidia{device_suffix}",
                 }
-                # Append to list of GRES lines for all models
                 gres_info.append(gres_line)
-
-                # Add to node parameters to ensure included in slurm.conf.
-                slurm_conf_gres = f"gpu:{model}:{len(devices)}"
-                try:
-                    # Add to existing Gres line.
-                    slurmd_info["Gres"].append(slurm_conf_gres)
-                except KeyError:
-                    # Create a new Gres entry if none present
-                    slurmd_info["Gres"] = [slurm_conf_gres]
+                slurmd_info["Gres"] = cast(list[str], slurmd_info.get("Gres", [])) + [
+                    f"gpu:{model}:{len(devices)}"
+                ]
 
         node = {
             "node_parameters": {

charms/slurmd/src/utils/gpu.py

@@ -22,7 +22,7 @@
 _logger = logging.getLogger(__name__)
 
 
-class GPUInstallError(Exception):
+class GPUOpsError(Exception):
     """Exception raised when a GPU driver installation operation failed."""
 
 
@@ -36,7 +36,7 @@ def __init__(self):
         try:
             apt.add_package(pkgs, update_cache=True)
         except (apt.PackageNotFoundError, apt.PackageError) as e:
-            raise GPUInstallError(f"failed to install {pkgs} reason: {e}")
+            raise GPUOpsError(f"failed to install {pkgs} reason: {e}")
 
         # ubuntu-drivers requires apt_pkg for package operations
         self._detect = _import("UbuntuDrivers.detect")
@@ -54,9 +54,8 @@ def _get_linux_modules_metapackage(self, driver) -> str:
         """
         return self._detect.get_linux_modules_metapackage(self._apt_pkg.Cache(None), driver)
 
-    def system_packages(self) -> list:
+    def system_packages(self) -> list[str]:
         """Return a list of GPU drivers and kernel module packages for this node."""
-        # Detect only GPGPU drivers. Not general purpose graphics drivers.
         packages = self._system_gpgpu_driver_packages()
 
         # Gather list of driver and kernel modules to install.
@@ -76,19 +75,14 @@ def system_packages(self) -> list:
                 # Add to list of packages to install
                 install_packages += [driver_metapackage, modules_metapackage]
 
-        # TODO: do we want to check for nvidia here and add nvidia-fabricmanager-535 libnvidia-nscq-535 in case of nvlink? This is suggested as a manual step at https://documentation.ubuntu.com/server/how-to/graphics/install-nvidia-drivers/#optional-step. If so, how do we get the version number "-535" robustly?
-
-        # TODO: what if drivers install but do not require a reboot? Should we "modprobe nvidia" manually? Just always reboot regardless?
-
-        # Filter out any empty results as returning
         return [p for p in install_packages if p]
 
 
 def autoinstall() -> None:
     """Autodetect available GPUs and install drivers.
 
     Raises:
-        GPUInstallError: Raised if error is encountered during package install.
+        GPUOpsError: Raised if error is encountered during package install.
     """
     _logger.info("detecting GPUs and installing drivers")
     detector = GPUDriverDetector()
@@ -102,10 +96,10 @@ def autoinstall() -> None:
     try:
         apt.add_package(install_packages)
     except (apt.PackageNotFoundError, apt.PackageError) as e:
-        raise GPUInstallError(f"failed to install packages {install_packages}. reason: {e}")
+        raise GPUOpsError(f"failed to install packages {install_packages}. reason: {e}")
 
 
-def get_gpus() -> dict:
+def get_all_gpu() -> dict[str, set[int]]:
     """Get the GPU devices on this node.
 
     Returns:
@@ -119,14 +113,12 @@ def get_gpus() -> dict:
     """
     gpu_info = {}
 
-    # Return immediately if pynvml not installed...
     try:
         pynvml = _import("pynvml")
     except ModuleNotFoundError:
         _logger.info("cannot gather GPU info: pynvml module not installed")
         return gpu_info
 
-    # ...or Nvidia drivers not loaded.
     try:
         pynvml.nvmlInit()
     except pynvml.NVMLError as e:
@@ -135,7 +127,6 @@ def get_gpus() -> dict:
         return gpu_info
 
     gpu_count = pynvml.nvmlDeviceGetCount()
-    # Loop over all detected GPUs, gathering info by model.
     for i in range(gpu_count):
         handle = pynvml.nvmlDeviceGetHandleByIndex(i)
 
@@ -146,15 +137,8 @@ def get_gpus() -> dict:
         model = pynvml.nvmlDeviceGetName(handle)
         model = "_".join(model.split()).lower()
 
-        # Number for device path, e.g. if device is /dev/nvidia0, returns 0
         minor_number = pynvml.nvmlDeviceGetMinorNumber(handle)
-
-        try:
-            # Add minor number to set of existing numbers for this model.
-            gpu_info[model].add(minor_number)
-        except KeyError:
-            # This is the first time we've seen this model. Create a new entry.
-            gpu_info[model] = {minor_number}
+        gpu_info[model] = gpu_info.get(model, set()) | {minor_number}
 
     pynvml.nvmlShutdown()
     return gpu_info

charms/slurmd/src/utils/machine.py

@@ -16,13 +16,16 @@
 
 import logging
 import subprocess
-from typing import Any, Dict
 
 _logger = logging.getLogger(__name__)
 
 
-def get_slurmd_info() -> Dict[str, Any]:
-    """Get machine info as reported by `slurmd -C`."""
+def get_slurmd_info() -> dict[str, str | list[str]]:
+    """Get machine info as reported by `slurmd -C`.
+
+    For details see:
+    https://slurm.schedmd.com/slurmd.html
+    """
     try:
         r = subprocess.check_output(["slurmd", "-C"], text=True).strip()
     except subprocess.CalledProcessError as e:
@@ -31,10 +34,10 @@ def get_slurmd_info() -> Dict[str, Any]:
 
     info = {}
     for opt in r.split()[:-1]:
-        key, value = opt.split("=")
-        # Split comma-separated lists, e.g. Gres=gpu:model_a:1,gpu:model_b:1
-        if "," in value:
-            info[key] = value.split(",")
-        else:
-            info[key] = value
+        k, v = opt.split("=")
+        if k == "Gres":
+            info[k] = v.split(",")
+            continue
+
+        info[k] = v
     return info