An Efficient Lock Protocol for Home-based Lazy Release Consistency Electronics and Telecommunications Research Institute (ETRI) 2001/5/16 HeeChul Yun

2/18 Contents Introduction Motivation Our Approach Performance Evaluation Conclusion

3/18 Introduction (1/2) SVM(Shared Virtual Memory) Page based software DSM Cost effective but performance is limited Proc1Proc2Proc3 ProcN Mem1Mem2Mem3MemN Network Shared memory abstraction

4/18 Introduction (2/2) Lazy Release Consistency (LRC) Most popular Allow multiple writer for a page using diff mechanism Home-based LRC (HLRC) Home is assigned for each page

5/18 HLRC (1/2) P0 Acq(L) P1 W(X) Rel(L) make twin fetch diff Acq(L) Invalidate R(X) create diff P0 Acq(L) P1 W(X) Rel(L) make twin Acq(L) Invalidate R(X) apply diff fetch page LRC HLRC P2(home) create diff

6/18 HLRC (2/2) Advantage No diff creation at Home Short lifetime of diff (low memory overhead) Problems Home assignment is important for performance Fetching a whole page on page fault  Poor lock performance

7/18 Motivation (1/2) Characteristics of lock protected data Migratory pattern Modification is small (fine grained) Poor lock performance of HLRC Proper fixed home assignment is difficult Migration schemes are not effective Fetching a whole page for small modification

8/18 P0 Acq(L) P1 W(X) Rel(L) Acq(L) Invalidate R(X) Fetch page P2(home) X(4byte) 4KB Apply diff Motivation (2/2)

9/18 Our Approach (1/5) Update small lock protected data Removing page fetching overhead Selectively piggyback diffs in lock grant message Diff selection metric Acquirer ’ s access history inside critical section Diff granularity

10/18 Our Approach (2/5) P0 Acq(L) P1 W(a) Rel(L) Acq(L) R(a) fetch page P2(home) apply diff P0 Acq(L) P1 W(a) Rel(L) Acq(L) R(a) P2(home) apply diff apply diff send diff create diff create diff HLRCOurs a Page X

11/18 Our Approach (3/5) Hint Access history Filter Only select small diff Apply Diff Lazy until fault occurs Acq(L) W(a) W(b) R(a) R(b) Rel(L) ACQ(X,Y) Diff(X0) P0 P1 Fetch page(Y) Hint (X, Y) Apply Diff(a) Filter Y a Page X b Page Y

12/18 Our Approach (4/5) Goodness No additional messages Lower message amount diff size < page size Avoid page requests inside critical section Small diff application is much faster than remote page fetching Minimize lock serialization

13/18 Our Approach (5/5) Overhead Home page diff creation Only for hinted page Stop if size is bigger than threshold Memory overhead for maintaining diffs Only for hinted page Simply free old diffs at some interval do not affect correctness  small overhead

14/18 Performance Evaluation Platform 8 node PIII 500Mhz Linux cluster 100Mbps switched Ethernet Implementation KDSM (KAIST Distributed Shared Memory) Base HLRC KDSM + Ours Application From SPLASH2 TSP, Water, Raytrace(o), Raytrace(r), IS

15/18 Page Requests Inside Critical Section

16/18 Message amount

17/18 Execution Time Breakdown

18/18 Conclusion Lock is inefficient in HLRC Home is at fixed location Whole page must be fetched on page fault Our Protocol Removing page fetching overhead for small data Improve lock performance with negligible overhead

19/18 Diff Creation X: Twin: Encode Changes X: Create Twin Write(x) Release Diff X: