1 Christmas special - Overview Assignment 9: hints  Scheduling Assignment 8: solution  Deadlocks

2 A9 Ex1 - Scheduling 5 jobs arrive at the same time Process turnaround time: the time elapsed from the submission of the job until the job was done JobTimePriority A103 B65 C22 D41 E84

3 A9 Ex1 - Scheduling Compute the average process turnaround time for:  Round robin  Priority scheduling  First-come, first-served (arrival: A, B, C, D, E)  Shortest job first

4 A9 Ex2 - Multithreading Some kernels allow for only one execution thread Multiple threads implemented in user- space Describe the difference between kernel threads and user-space threads (hints: system-call cost, access to kernel structures).

5 A9 Ex3 - Processes What are the differences between threads and processes? Compare the data to be saved during a context switch for:  Coroutines (Oberon)  Threads  Processes

6 c.send(msg) c.receive(msg) Process AProcess B channel c synchronization PEx1 – CSPs

7 PEx1 - Erathostenes’ Sieve Number Generator Filter Filter Filter Filter 7 The numbers dividable with the filter number are dropped The other numbers are passed to the next filter If no filter exists, create one

8 PEx2 - How big should a TLB be? A TLB miss requires 20 instructions iTLB configurations  128 entries, two-way assoc, 4-64 KB pages  512 entries, two-way assoc, 4-64 KB pages Use SimpleScalar simulator and one or more SPEC2000 benchmarks to calculate  Instruction TLB miss rate  Instruction TLB overhead: percentage of time wasted handling TLB misses

9 PEx2 - How big should a TLB be? Download SimpleScalar and the SPEC2000 binaries Type./sim-cache –h Default = 16 sets, 4 KB pages, four-way assoc, LRU replacement A new configuration for data TLB is set by./sim-cache –tlb:dtlb dtlb:128:8192:4:r

10 Christmas special - Overview Assignment 9: hints  Scheduling Assignment 8: solution  Deadlocks

11 A8 Ex1 - Barrier (Java) public class Barrier { private static int N; private static int count; public Barrier(int n) { N = n; count = 0; } public void synchronized enter() { if (count++ == N) { notifyAll(); count = 0; } else { wait(); }

12 A8 Ex1 - Barrier (Active Oberon) MODULE Barriers; TYPE Barrier = OBJECT VAR n, N: LONGINT; PROCEDURE Enter*; VAR i: LONGINT; BEGIN {EXCLUSIVE} i := n DIV N; INC(n); AWAIT (i < n DIV N) END Enter; PROCEDURE & Init (nofProcs: LONGINT); BEGIN N := nofProcs; n := 0 END Init; END Barrier; END Barriers.

13 A8 Ex2 - Deadlock Avoidance Ordering  the resources are ordered  a lock manager assigns lock using priorities (e.g. the account with the lower number gets the lock first). Two-phase locking

14 A8 Ex1 - Baboons Semaphore  starvation is possible Ticketing system  tickets are released when a process (baboon) request access to the resource (rope)  access is granted to process with tickets (in increasing order)

15 Merry Christmas!