Testing HCN for PRAM Michael Jones, Ganesh Gopalakrishnan University of Utah, School of Computing

Outline Goals: –re-use an abstraction for branching topologies –combine test model checking and abstraction How HCN works What was verified and how Discussion

HCN Directory-based hierarchical caching netw. Obeys sequential consistency, and PRAM is weaker than SC. Written by Arvind and Xiaowei Shen

HCN Model P P PPPP M M MM M M M M M

P P PPPP M M MM2 M M M0 M M1 wr_req (a,2) ex-req(a)

HCN Model P P PPPP M M MM2 M M M0 M M1 wr_req (a,2) ex-req(a)

Testing for PRAM Any 3 processors Located anywhere in any HCN network Sharing a single address Always satisfy PRAM Abstraction to cover all networks Test model check for PRAM with N=3.

Testing for PRAM # Procs sharing address:3 # Procs in system:arbitrary # Caches in system:arbitrary # Addresses being shared1 # Addresses in systemarbitrary Propertymem model

Abstraction Recipe 1.Throw away enough transactions and structure, and... 2.Merge enough structure to get a finite state model. 3.Add enough non-determinism to get same behavior on remaining observed state (Inspired by trace inclusion refinement)

Why the Recipe Works For some class of protocols, a “nice amount” of non-determinism is required to capture all behaviors of the observed state in the reduced model

HCN Abstraction M M MM2 M M M0 M M1

HCN Abstraction M M MM2 M M M0 M M1 P QP

HCN Abstraction M M MM2 M M M0 M M1 P QP

HCN Abstraction M M M0 M M1 P QP

Merging Linear State M M M...

HCN Abstraction M M M0 M M1 P QP PPQ

|{Finite State Configs}| is Finite PPQPPQPPQ

Modeling a TRS in Mur  Rule "receive wb rep and send sh rep" (trec[addr].req = sh_req & hd_in.opc = wb_rep & hd_in.addr = addr & state[addr] = ex_w & (current_writer(addr,m) = hd_in.src)) ==> var rep_msg : tMsg ; begin rep_msg.opc := sh_rep; rep_msg.src := m; rep_msg.dst := trec[addr].id; rep_msg.addr := addr; rep_msg.data := hd_in.data; enqueue (outq, rep_msg); state[addr] := ex_r; add_to_dir (addr, trec[addr].id, m, dir); add_to_dir (addr, hd_in.src, m, dir); clearTrec (addr,trec); delete (inq, 0); end; receive-wb-rep-and-send-sh-rep <id,Cell(a,u,(Ex,W(idk)))|m, Msg(idk,id,Wbrep,a,v)+i,o, Trec(a,(idp,Sh-req))|t>  <id,Cell(a,v,(Ex,R(idk|idj)))|m, i,o+Msg(id,idj,sh-rep,a,v), t>

Testing for PRAM wr(A,2) rd(A,-) wr(A,2) rd(A,-) rd( A,1 ) rd(A,0) E wr(A,0) rd(A,-) wr(A,1)rd(A,-) wr(A,1) rd(A,1) E wr(A,1) rd(A,-) rd(A,0) Model Checker

Inadvertantly Seeded Error

Model Checking Results PPQ PQP PPQ StatesCPU time (sec) 110, Total 881, , ,

Discussion  at least one error in which topology matters Abstraction carried over nicely to a non-PCI protocol. N=4 and 2 addresses: both too big. –only explore several million states per model Abstraction + test model checking = more general results.

Inadvertantly Seeded Error read&miss sh-req

Inadvertantly Seeded Error read&miss sh-req write&miss ex-req

Inadvertantly Seeded Error read&miss sh-req write&miss ex-req write&miss ex-req

Inadvertantly Seeded Error read&miss sh-req write&miss ex-req write&miss ex-req ex-req(2) 1 0 2

Inadvertantly Seeded Error read&miss sh-req write&miss ex-req write&miss ex-rep 1 0 2:0

Inadvertantly Seeded Error read&miss sh-req write&miss ex-req write&miss wb-req ex-req(1) 1 0 2:0

Cache State Encoding M State Address Value Cache Home cell... cell

Cache State Encoding State Address Value Cache Home cell... cell “Cstate”: Shared or exclusive wrt siblings “Horizontal” state Sh = shared with siblings Ex = has an exclusive copy.

Cache State Encoding State Address Value Cache Home cell... cell “Hstate”: Which children have cached the state and why “Vertical” state R(dir) = all children in dir have shared copies for reading W(id) = the child id has an exclusive copy for writting

HCN Model P P PPPP M M MM2 M M M0 M M1 M1 is a child of M0, so M1 is a cache for data in M0.

HCN Model P P PPPP M M MM2 M M M0 M M1 M1 is the parent of M2, so M1 is the home of data in M2

HCN Model P P PPPP M M MM M M M M M Innermost memories, or L1 caches.

HCN Model P P PPPP M M MM M M M M M Outermost memory

Testing for PRAM wr(A,2) rd(A,-) wr(A,2) rd(A,-) rd(A,1) rd(A,0) E wr(A,0) rd(A,-) wr(A,1)rd(A,-) wr(A,1) rd(A,1) E wr(A,1) rd(A,-) rd(A,0)

HCN Model P P PPPP M M MM2 M M M0 M M1 wr_req (a,2) ex-req(a) wb-req(a)

HCN Model P P PPPP M M MM2 M M M0 M M1 wr_req (a,2) ex-req(a) wb-req(a)