1537crumtualiztion1 Mechanisms HIScheduling2 Police
noosingwhichprocess to run
mechanisms at once
TunNprocesseswhile Os maintains
controlsecurity protection
robustness
efficiently
steps
TBoot Start up
Os runs first establishcontrol
of machine
setsIgeminds to handlevarious service requests
e.ggead a file
app issues a systemcall
Dissuatrapspecial inst
key thing on trapApp SOS
switch motesfrom user kernel
non
privileged privilegedwhen done
refyfromTime line
YET Meat
osl ti t
How to run many processesat once
Pa PB Pa P
time sharingHood problem
A Process may run
for a long time
Q how to OS regaincontrol Pu
A timer interruptboot set this up
interrupt the CPU
every 1 milliseconds
If I PB7 ter r
intisaverestate offalots
restore stateof PB
context switch
OS responsibilitytractor each process State
RunningReady not running
could be
what if Process does
something slow
disk I o
Pa readtrap
CPU dOS
g
manyU milliseconds
Hdesire diskswitch to some other process
when I 0 is issued
mark Pa as Blocked
CuaitingtonI10
switch to PB
Ilo completesmark Pa as Ready
Empletesdesched
schedule
ning Blockedissue
OS Cpu an Ilo
scheduler
U
ossify queue
FFisionthanks
I É
ight intro to
I É
FileSchedler mem
yqsystemchoosing of
simplifyingAssumptions about workload
set Tfprocessesprofit that Os needs
to run
Assumptionstart all jobsarrive once
just use CPU no I10
fixed length runs for time T
time is known
metric turnaround time
T T completes Tarrives
Algorithm IT FI FOIF CFS
A B C arrive to
run time I
Avg TurnaroundActs assuming FIFO
AIME
TA L TB Tc 31
Relax Assumption 3
A B C10 100 10
f EffectAE
T.toTang 80
Newisfestjohti
TAVG
All jobs don't arrive at once
A 100
rumB
É
B arrives
B 1
Shortest time to CompletionFirst STC F
