Add niceness configuration for process priority control (#264)

Introduce the `HORIZON_NICENESS` configuration to control the process niceness value, enabling better CPU resource allocation. Implemented `set_process_niceness` to adjust the process priority based on the specified value, with safety checks and logging for status and errors. This ensures processes can be fine-tuned for performance or background execution as needed.

Author: danyi1212

horizon/config.py

@@ -265,6 +265,16 @@ def parse_plugins(value: Any) -> dict[str, dict[str, int | bool | str]]:
         description="The path to the file that contains the PDP version",
     )
 
+    HORIZON_NICENESS = confi.int(
+        "HORIZON_NICENESS",
+        10,
+        description=(
+            "The niceness value for the PDP Horizon process (Python process). "
+            "Niceness values range from -20 (highest priority) to 19 (lowest priority) with 0 is neutral. "
+            "Adjusting this can help manage CPU resource allocation. "
+        ),
+    )
+
     @staticmethod
     def parse_callbacks(value: Any) -> list[CallbackEntry]:
         if isinstance(value, str):

horizon/pdp.py

@@ -1,4 +1,5 @@
 import logging
+import os
 import sys
 from pathlib import Path
 from uuid import UUID, uuid4
@@ -45,6 +46,37 @@
 OPA_LOGGER_MODULE = "opal_client.opa.logger"
 
 
+def set_process_niceness(target_nice: int) -> None:
+    """
+    Attempts to set the current process's niceness value to `target_nice`.
+    This operation is performed only once during the call.
+
+    This function is idempotent if the current niceness already equals `target_nice`.
+    Setting a lower niceness value (increasing priority) may require CAP_SYS_NICE
+    capabilities and could fail if the process lacks sufficient privileges.
+    """
+    if target_nice < -20 or target_nice > 19:
+        raise ValueError(f"Target niceness must be between -20 and 19, got {target_nice}")
+
+    try:
+        current_niceness = os.nice(0)  # Read current niceness without changing it
+        delta = target_nice - current_niceness
+        if delta != 0:
+            os.nice(delta)  # Apply the change
+            new_niceness = os.nice(0)  # Read the new niceness to confirm
+            logging.info(
+                "Changed the process niceness by %d from %d to %d (target was %d).",
+                delta,
+                current_niceness,
+                new_niceness,
+                target_nice,
+            )
+        else:
+            logging.debug("Process niceness is already %d, which matches the target; no change made.", current_niceness)
+    except OSError as exc:
+        logging.warning("Failed to change process niceness to %d: %s", target_nice, exc)
+
+
 def apply_config(overrides_dict: dict, config_object: Confi):
     """
     apply config values from dict into a confi object
@@ -131,6 +163,9 @@ def __init__(self):
         if sidecar_config.ENABLE_MONITORING:
             self._configure_monitoring()
 
+        if sidecar_config.HORIZON_NICENESS:
+            set_process_niceness(sidecar_config.HORIZON_NICENESS)
+
         self._opal = OpalClient(shard_id=sidecar_config.SHARD_ID, data_topics=self._fix_data_topics())
         self._inject_extra_callbacks()
         # remove default data update callbacks that are not needed and might be managed by the control plane