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from __future__ import division
from math import ceil, floor
def charge_initial_load(oheads, taskset):
"""Increase WCET to reflect the cost of establishing a warm cache.
Note: assumes that .wss (working set size) has been populated in each task.
"""
if oheads:
for ti in taskset:
load = oheads.initial_cache_load(ti.wss)
assert load >= 0 # negative overheads make no sense
ti.cost += load
if ti.density() > 1:
# infeasible
return False
return taskset
def preemption_centric_irq_costs(oheads, dedicated_irq, taskset):
n = len(taskset)
qlen = oheads.quantum_length
tck = oheads.tick(n)
ev_lat = oheads.release_latency(n)
# tick interrupt
utick = tck / qlen
urel = 0.0
if not dedicated_irq:
rel = oheads.release(n)
for ti in taskset:
urel += (rel / ti.period)
# cost of preemption
cpre_numerator = tck + ev_lat * utick
if not dedicated_irq:
cpre_numerator += n * rel + ev_lat * urel
uscale = 1.0 - utick - urel
return (uscale, cpre_numerator / uscale)
def charge_scheduling_overheads(oheads, num_cpus, dedicated_irq, taskset):
if not oheads:
return taskset
uscale, cpre = preemption_centric_irq_costs(oheads, dedicated_irq, taskset)
if uscale <= 0:
# interrupt overload
return False
n = len(taskset)
wss = taskset.max_wss()
sched = 2 * (oheads.schedule(n) + oheads.ctx_switch(n)) \
+ oheads.cache_affinity_loss(wss)
irq_latency = oheads.release_latency(n)
if dedicated_irq:
unscaled = 2 * cpre + oheads.ipi_latency(n) + oheads.release(n)
elif num_cpus > 1:
unscaled = 2 * cpre + oheads.ipi_latency(n)
else:
unscaled = 2 * cpre
for ti in taskset:
ti.period -= irq_latency
ti.deadline -= irq_latency
ti.cost = ((ti.cost + sched) / uscale) + unscaled
if ti.density() > 1:
return False
return taskset
def quantize_params(taskset):
"""After applying overheads, use this function to make
task parameters integral again."""
for t in taskset:
t.cost = int(ceil(t.cost))
t.period = int(floor(t.period))
t.deadline = int(floor(t.deadline))
if not min(t.period, t.deadline) or t.density() > 1:
return False
return taskset
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