B.N. Bershad, T.E. Anderson, E.D. Lazowska and H.M. Levy
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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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B n bershad t e anderson e d lazowska and h m levy lightweight remote procedure call acm transactions on compute

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


Presentation outline
Presentation outline

  • What is LRPC?

  • O.S. communication – most common case

  • LRPC execution model

  • Performance of LRPC

  • Conclusions


What is lrpc
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


O s communication the common case cross domain vs cross machine
O.S. communication - the common caseCross-domain vs cross-machine

Vast majority of calls do not cross machine boundaries


O s communication the common case size and complexity of calls

~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


O s communication the common case performance i
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”


O s communication the common case performance ii
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…


Lrpc execution model
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


Binding 1
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


Binding 2
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)


Calling
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


Optimization 1 argument copying

A-stack

Optimization 1Argument copying

RPC

LRPC

A-stack: Read-write and shared by both domains


Optimization 2
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…)


Optimization 3
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


Performance of lrpc 1
Performance of LRPC - 1

  • Average on 100,000 cross-domain calls

  • LRPC/MP uses domain caching

  • TAOS uses RPC

  • Taos/LRPC ~= 3!


Performance of lrpc 2
Performance of LRPC - 2

  • The “context switches” cost is what domain caching helps reduce

  • Single processor: LRPC adds only 48ms


Performance of lrpc 3
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


Conclusions
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?)


References
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