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Mini Shell
# coding=utf-8
#
# Copyright © Cloud Linux GmbH & Cloud Linux Software, Inc 2010-2023 All Rights Reserved
#
# Licensed under CLOUD LINUX LICENSE AGREEMENT
# http://cloudlinux.com/docs/LICENSE.TXT
from collections import deque
from typing import NamedTuple, Self, Protocol
from ._logs import logger
class StatsTimes(NamedTuple):
@classmethod
def from_proc_stat(cls, line: str) -> Self:
# NOTE(vlebedev): First element of the line is a name of a CPU core, not time of any kind.
return cls(*(int(v) for v in line.strip().split()[1:]))
user: int
nice: int
system: int
idle: int
iowait: int
irq: int
softirq: int
steal: int
guest: int
guest_nice: int
class GetStats(Protocol):
def __call__(self) -> StatsTimes:
...
class OverloadCheckResult(NamedTuple):
is_overloaded: bool
server_load: float
def __bool__(self) -> bool:
return self.is_overloaded
class OverloadChecker:
def __init__(
self,
idle_time_threshold: float,
get_stats: GetStats,
max_samples_number: int,
) -> None:
self._prev_stats = None
self._idle_time_threshold = idle_time_threshold
self._weights = _get_weights(num=max_samples_number)
self._idle_times_history = deque(maxlen=max_samples_number)
self._get_stats = get_stats
self._max_samples_number = max_samples_number
def __call__(self) -> OverloadCheckResult:
stats = self._get_stats()
# NOTE(vlebedev): 'delta' represents total time spent by CPU
# on all kinds of activities since the previous measurement.
delta = stats if self._prev_stats is None else StatsTimes(*(
new - old
for (new, old)
in zip(stats, self._prev_stats)
))
self._prev_stats = stats
# NOTE(vlebedev): Fraction of total delta time spent by CPU on being 'idle'.
try:
idle_time = delta.idle / sum(delta)
except ZeroDivisionError:
idle_time = 0.0
self._idle_times_history.append(idle_time)
samples_num = len(self._idle_times_history)
relevant_weights = self._weights[:samples_num]
weighted_idle_times = [
weight * idle_time
for weight, idle_time
in zip(relevant_weights, self._idle_times_history)
]
weighted_idle_time = sum(weighted_idle_times)
if samples_num < self._max_samples_number:
weighted_idle_time /= sum(relevant_weights)
logger.debug('Current idle time: %02.2f, threshold %s', weighted_idle_time, self._idle_time_threshold)
return OverloadCheckResult(
is_overloaded=weighted_idle_time < self._idle_time_threshold,
server_load=1-weighted_idle_time,
)
def _get_weights(num: int = 10, alpha: float = 0.9):
# NOTE(vlebedev): Generate an exponentially decaying weight list
weights = [alpha ** i for i in range(num)]
# NOTE(vlebedev): Normalize the weights so they sum to 1
total = sum(weights)
return [weight / total for weight in weights]
def read_times_from_proc() -> StatsTimes:
with open('/proc/stat', encoding='ascii') as fd:
return StatsTimes.from_proc_stat(fd.readline())
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