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Lanfranco Muzi PSU – April 21 th , 2005

B.N. Bershad, T.E. Anderson, E.D. Lazowska and H.M. Levy Lightweight Remote Procedure Call ACM Transactions on Computer Systems, Vol.8, No.1, February 1990, 37-55. Lanfranco Muzi PSU – April 21 th , 2005. Presentation outline. What is LRPC? O.S. communication – most common case

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Lanfranco Muzi PSU – April 21 th , 2005

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  1. B.N. Bershad, T.E. Anderson, E.D. Lazowska and H.M. LevyLightweight Remote Procedure CallACM Transactions on Computer Systems, Vol.8, No.1, February 1990, 37-55 Lanfranco Muzi PSU – April 21th, 2005

  2. Presentation outline • What is LRPC? • O.S. communication – most common case • LRPC execution model • Performance of LRPC • Conclusions

  3. What is LRPC? • A communication facility designed and optimized for communication between protection domains in the same machine • Target: small-kernel operating systems • separate components placed in disjoint domains • messages used for interdomain communication

  4. O.S. communication - the common caseCross-domain vs cross-machine Vast majority of calls do not cross machine boundaries

  5. ~70% O.S. communication: the common caseSize and complexity of calls • 95% of calls to 10 procedures • 75% to 3 procedures! • Most frequent case: less than 200 bytes Vast majority of calls: small, simple arguments/results

  6. O.S. communication: the common casePerformance (I) “In existing RPC systems, cross-domain calls are implemented in terms of the facilities required by cross-machine ones”

  7. O.S. communication: the common casePerformance (II) • “Theoretical minimum”: 2 traps and 2 context switches • Overhead: stub, message buffer, access validation, message transfer (queues), scheduling (independent threads), context switches…

  8. LRPC execution model • Client binds to server before making first call • Call causes kernel trap • Kernel: validate caller, create linkage, dispatch client’s thread to server • Thread executes in server • Control (and thread) back to kernel and caller

  9. Binding - 1 • Different from RPC • “Import” call from client via kernel • Server provides Procedure Descriptor List, used by kernel to allocate A-stacks and create linkage record • At completion, kernel returns to client a Binding object and A-stack list

  10. Binding - 2 A-stack: Read-write and shared by both domains Linkage record: Records caller’s return address + current SP Binding object: Client’s key to interface (must be presented to kernel at every call)

  11. Calling Client stub: • Pop A-stack off the queue, push arguments • Put A-stack address, Binding Object and procedure identifier into registers • Trap Kernel: • Validation etc. • Find E-stack in server domain and update user thread stack pointer • Reload CPU virtual memory registers with those of the server domain

  12. A-stack Optimization 1Argument copying RPC LRPC A-stack: Read-write and shared by both domains

  13. Optimization 2 • Stub: choice between cross-domain or –machine in 1st line • Validation: only on call (linkage is in thread’s control block on return) • Scheduling in RPC: different threads in each domain signalling at each other (block client, dispatch in server…)

  14. Optimization 3 Multiprocessors: • Reduced lock contention: each A-queue has its own lock – no other locking required • Reduced context-switch overhead: Domain caching on idle processors – move to idle CPU avoiding context switch

  15. Performance of LRPC - 1 • Average on 100,000 cross-domain calls • LRPC/MP uses domain caching • TAOS uses RPC • Taos/LRPC ~= 3!

  16. Performance of LRPC - 2 • The “context switches” cost is what domain caching helps reduce • Single processor: LRPC adds only 48ms

  17. Performance of LRPC - 3 Call throughput on a multiprocessor • Domain caching disabled • RPC scales poorly due to lock contention, which is very limited in LRPC

  18. Conclusions • LRPC adopts an optimized approach to the most common case in O.S. communication • Performs well on the majority of PC between address spaces on the same machine • Avoids unnecessary synchronization, kernel-level thread management and data copying • LRPC performs better than RPC in the common case, and scales better on multiprocessors • Authors conclude that it is a good communication alternative for small-kernel O.S. (further developments?)

  19. References • B.N Bershad et al. “Lightweight remote procedure call” ACM Trans. Comput. Syst. 8,1 (Feb.1990) 37-55 • A.D. Birrel et al. “Implementing remote procedure calls” ACM Trans. Comput. Syst. 2,1 (Feb.1984) 39-59 • B.N. Bershad et al. “User-level interprocess communication for shared memory multiprocessors” ACM Trans. Comput. Syst. 9,2 (May1991) 175-198 • A.S. Tanenbaum “Modern Operating Systems” 2nd ed. Prentice Hall (RPC: 534-540) • Silberschatz, Galvin, Gagne “Operating system concepts” 6th ed., John Wiley & Sons (RPC: 117-124) • “Remote procedure calls” Pznan University of technology – Institute of computing Science http://skisr.cs.put.poznan.pl/download/rso/lec/w4_rpc.doc

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