Key Issues of Resource Management in Distributed

Multimedia Computer Systems

Zhang Zhanjun Yang Xueliang Han Chengde

Graduate School of University of Science and Technology of China, Beijing, I00039 Institute of Computing Technology, Chinese Academy of Science, Beijing, I00080

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Abstract: The guarantee of quality of service (QoS) of multimedia applications is a kernel issue in resource management of distributed multimedia computer systems. Some key issues are done research for resource management in multimedia transmission in this paper as follows. ( I ) the relation between QoS and resource management, (2) the algorithm of scheduling distributed multimedia tasks, (3) the paradigm of session-based distributed multimedia resource allocation.

Key Words: QoS, scheduling tasks, session, resource management.

1. Introduction

The guarantee of quality of service (QoS) of multimedia applications is a kernel issue i n resource management of distributed multimedia computer

systems. For example, a video stream requires QoS including end-to-end delay 100ms. CPU, I/O and buffers should be allocated appropriately for guarantee of the delay in computer systems. Bandwidth should be allocated appropriately to guarantee the delay in network systems. It is an important issue how to allocate these resources. The application's QoS can not be guaranteed if required resources can not be allocated. The resources can not be utilized effectively if excessive resources are

allocated so that the resources are wasted. The relation between QoS and resource management and the content of resource management are analyzed in this paper. This paper focuses on the scheduling tasks and resource allocation. This paper does research for the algorithm of scheduling multimedia tasks because the algorithm has impact on CPU management. This paper does research for the paradigm of resource allocation for CPU, I/O, buffers and network bandwidth using the producer - consumer model, and presents the paradigm of session-based resource cquilibriuni allocation for guarantee of steady flow.

2. Related Work

Most of algorithms of scheduling distributed multimedia tasks are from real-time systems e.g. EDF and RM. They are periodic scheduling algorithms. The pinwheel scheduling is based on a Distance- Constrained Task System (DCTS), unlike periodic scheduling, enables scheduling no jitter so that it is very suitable for the distributed multimedia systems. Han presented a single-node pinwheel algorithm, Sr . Hsueh extended Sr to the DSr algorithm so that multiple nodes are processed. However, the definition of DCTS of DSr algorithm is very simple so that it

can not be utilized in real multimedia systems. Mehra discussed resource management in real-time

' This work was supported by the Chinese National Science Foundation 69983007.

0-7803-6394-9/00/$10.00O2000 IEEE.

systems. Huang presented resource management model for continuous multimedia database applications in uni-processor system, and studied a paradigm of allocation of threads, I/O processes and buffers. Nahrstedt presented the content and key issues of resource management for network multimedia applications.

3. QoS and Resource Management

CPU, memory (buffers), I/O (disk I/O and multimedia device UO), bus bandwidth and network bandwidth are shared resources in distributed multimedia computer systems. The bus bandwidth is dynamically allocated by operating system according to processes or threads executing so that it can not be managed by application process. T~LIS , it is not studied in this paper. Some appropriate resources should be allocated for guarantee of application's QoS. The application's QoS can not be guaranteed if required resources can not be allocated. For example, CPU, memory, I/O and network bandwidth should be allocated for guarantee of end-to-end delay in QoS in computers along end- to-end path. Thus, resource management is relative to the QoS and the guarantee of application's QoS is premise of resource management. Sometimes, The QoS of a few applications can not be met as exhausted resources. For example, a video stream requires a 640K byte buffer. But there is only 540K byte available memory in system. Thus, The utilization of resources should be improved effectively for guarantee of QoS of the more applications'. When system allocates resources for each application, excessive resources can not be allocated

4. Multimedia Task Scheduling

4.1 Scheduling Algorithm in Real-Time System

The most of scheduling algorithm are periodic in real-

time system. The time constraints of the periodic task Tare characterized by the following parameters T(s, e,

d, d r ) . s: Starting point e: Processing time of T d: Deadline of T p : Period of T I-: Rate of T (i-=l/p) where O$e<'d$p. The starting point s is the first time when the periodic task requires processing. Subsequently, it requires processing in every period with a processing time of e. At s+(k-I)p, the task T is ready for /-processing. The processing of T in period k must be finished at s+(l;-l)p+d. For continuous media tasks, it is assumed that the deadline of the period (k-I ) is the ready time of period k .

(1) The Earliest Deadline First (EDF) algorithm is one of the best-known algorithms for real-time processing. At every new ready state, the scheduler selects the task 7; with the earliest deadline dl among the tasks {7? that are ready and not fully processed. The requested resource is assigned to the selected task. At any arrival of a new task q, EDF must be computed immediately leading to a new order: the running task T, is preempted and the new task T, is scheduled according to its deadline (Il. The new task T, IS

processed immediately if its deadline a'/ is earlier than that of the interrupted task T,. The processing of the interrupted task is continued according to the EDF algorithm later on. Given a task set T={T,, q, ... TI ) , EDF is guaranteed to find a feasible schedule for T if

Earliest Deadline First Algorithm (EDF)

(2) Rate Monotonic Algorithm (RM) (a) The rate monotonic scheduling algorithm is an optimal, static, priority-driven algorithm for preemptive, periodic jobs. The order of tasks is computed before tasks in {TI are scheduled. Subsequently, each task is processed with the priority

calcplated according to its rate at the beginning. The faSter rate i i a task is, the higher its priority is. If tasks TI and T, are given by u,<r,, their priority are defined

Given a task set T={T1, T,, ... TIS, RM is guaranteed to find a feasible schedule for T if

by P/'l<Pr/.

I1

C e i i p i I n ( 2 " " -1). ,=I

I .2 Distributed Multimedia Task Scheduling

In some real-time applications, task must be executed i n a distance-constrained manner, rather than just periodically. That is, the temporal distance between any two adjacent executions of the same task should always be less than a certain amount of time. Such real-time systems are called Distance-Constrained Task System (DCTS) [9]. The pinwheel scheduling is based on the DCTS and it is very suitable for the distributed multimedia systems with jitterless. Definition 1: Let X={Xi) I <i g n , be a set of distribh'ed multirriedia tasks. Suppose the number of tasks (transactions) I S n, and the number of nodes is nz.

For YX E X , XI = { T , , } , ~ E {l . . . R z } ~ let T,,be the

task of X, executing on node NI. TI, has the distance constraint c,, and executing time e,/. Definition 2: Given a set of scheduling multimedia tasks x as DCTS,

density of X in node NI. Theorem 1: Given a set of scheduling multimedia tasks X as DCTS, i fX is met in any nodes N,

Z , ( x ) 5 P = P r ' ,

then DMSr is guaranteed to find a feasible for X; where 17, is number of tasks in N, .Moreover, the bound Bis tight.

5. Session-based Resource Allocation

Definition 3: There are n multimedia streams in system. The multimedia stream can be described as the session .$-( Ai, 78 g' 8, i=1,2 ,... , n [ IO]. .Ii-the target rate of media data flow specified from

the end-user perspective. It is defined by data units per second, where a data unit can be a video frame or a group of audio samples consisting of a certain number of bytes. ; F a set of threads q,(j=1,2 ,... in, m 1 2 / ) that

execute 5 !i is defined by rj/ (4, 6 $, where 4 is its execution period, $ is its CPU time or period for processing one media data unit, 3 is the number of data units processed within each period, and F; . . XTis the executing time of thread r,? p a set of buffers k(j=/,2 ,...,I,

such as a video frame and $is the number of such

data units allocated in the buffer. Hence, a buffer size

113/) allocated for +' is defined by y, #, where z,j is a media data unit

is pq +-an I/O process that carries out the I/O requests of $' +is defined by Sy g q $, where Tis the I/O request

period, q is the unit of media data on device (disk), and Tis the number of allocated units to be accessed within each period p F a set of network processes 7/(7=/,2,. ..., h,

that execute network transmission of $ yi is defined

by y j ( q , 5, $, where 4 is period of network processing, 5 is transmitting unit in network, a i s number of media units transmitted per period (3.

hj&)

Theorem 2: There are n sessions &,5( AI, 78 g' $< i= / ,2 , ...,a in system and there are one I/O process, nz,

threads, and h, network processes in session S,. The period of I/O processing r,, the period of threads p,/ , / Sj </77,,, and period of network processing q,/ , / S'j S' h, are allocated by the number of media units x,,

processed as follow.

Xl(X + 1 1 1 1 )

XI ( h + ,111 + I ) q l k = x q i ( h + I ) 1 I IC < hi

xi ( k + 111, )

X I ( , + I )

q l k =- x pi( j + I IC = hi, j = m i + 1

j = ml 1

= ;k Theorem 3: Given a session ?with m, threads, hl network processes, and inl +hl buffers. The utilization of CPU VI, buffers MI, l/O bandwidth Z,, and network bandwidth J , are allocated by the nuniber of media units x,, processed as follow.

/=I

Lli lXXlO = - = auil

I‘i

6. Conclusion

The guarantee of quality of service (QoS) for

distributed multimedia streams greatly challenges resource management in computer systems and network systems. Resources in networks and computers should be allocated according to the QoS. There is close relation between resource management and QoS. The essential of resource management is the guarantees of QoS. Most of algorithms of scheduling multimedia tasks are from real-time system such as EDF, RM, which are periodic. This paper presents a

distance constraint-based sclicduliiig algorithm DMSr which pinwheel bases are calculated step by step in all nodes in parallel. A paradigm of session-based resource allocation is presented for steady rate of multimedia streams in this paper. When resources are allocated, it can calculate the resources for steady continuous multimedia streams by making equilibrium equations among process or thread’ s

periods, I/O processor’s periods, buffer space and network bandwidth. Fuithermore, we will study distributed session scheduling with adaptive network bandwidth availability, for example Internet.

References

[ l ] Marco Di Natale, John A Stankovic, Dynamic End-to-end Guarantees in Distributed Real-Time Systems, Proceeding of Real-Time System Symposium, 1994 [2] Hiroyuki Kaneko, John A. Stankovic, et al, A Multimedia Server on the Spring Real-Time System, IEEE Real-Time Technology and Applications Symposium, MA, June, 1996

Zhang Zhanjuii received his BS in computer science from HeBei University in 1988 and his Ph.D in computer science from University of Science and Technology of China in 1996. Currently, he is a post- doctor researcher. His current research interests include the multimedia transmission, distributed computer systems and network protocols.