Sharing Patterns

• Producer-consumer (initially flag, done are zero)

  T0: while (!exit) {x=y; flag=1; while (done != k);
  flag=0; done=0;}
  T1 to Tk : while (!exit) {while (!flag); use x;
  done++; while (flag);}

• Exit condition not shown
• What if T1 to Tk do not have the outer loop?
• Migratory (initially flag is zero)

  T0: x = f0(x); flag++;
  T1 to Tk : while (flag != pid ); x = f1(x); flag++;

• Migratory hand-off?

Migratory Hand-off

• Needs a memory writeback on every hand-off
  • r0, w0, r1 , w1, r2 , w2, r3 , w3, r4 , w4, …
  • How to avoid these unnecessary writebacks ?
  • Saves memory bandwidth
  • Solution: add an owner state (different from M) in caches
  • Only owner can write a line back on eviction
  • Ownership shifts along the migratory chain