New Stream Caching Schemas for Multimedia Systems J. Fernandez 1 , J. Carretero 2 , F. Garcia-Carballeira 3 , A. Calderon 4 and J. M. Perez-Menor 5 Computer Architecture Group, Computer Science Department, Universidad Carlos III de Madrid, Leganes, Madrid, Spain. E-mail:{jfernand,jcarrete,fgarcia,acaldero}mperez@arcos.inf.uc3m.es} Abstract In this paper a new multimedia caching strategy is proposed that includes several optimizations to the state of the art. This algorithm takes its roots from the interval caching algorithms but it evolves towards a more adaptive approaching that could obtain a better performance for variable bit-rate streams and serving media stored on multiple disks following different distributions. All of this without loosing competitiveness for constant bit-rate streams on a single disk. All this efforts are oriented towards the consecution of MUPIC (Multi Policy Integrated Cache), a cache architecture designed to fit the requirements of an integrated storage system that meet the requirements of deterministic applications, multimedia systems, and traditional best-effort applications altogether. 1. Introduction Over the last years, there has been a great interest on optimizing the I/O performance, especially on the scheduling of I/O devices, but also on the cache policies, in computer systems [17,11] However, the requirements and the platforms for both multimedia and general systems seemed to be so different [13] that people developed specialized systems. Thus, disk scheduling algorithms and cache policies for general purpose systems tried to reduce the access time, while multimedia systems tended to satisfy the real-time constraints for cyclical streams, even loosing performance. With the multimedia applications increasing, some authors [16] have proposed the design of a new kind of system, named integrated, that includes facilities to support heterogeneous multimedia and general purpose information. In an integrated system, the user may request the start of a new I/O request (stream) during run-time. The system must determine, following some admission criteria, whether the stream is schedulable to admit or reject the stream. The main problem with most of those systems is that they do not provide schedulability guarantees for deterministic applications [7]. In this paper we describe a new multimedia cache algorithm that imposes several optimizations to the state of the art. All the work described in this paper is oriented towards the development of a multimedia integrated parallel file system called MiPFS [5]. For this system, a Multi policy Integrated cache (MUPIC) is proposed. This cache integrates different caching policies: multimedia policy dedicated to requests with real-time requirements that fit into multimedia access patterns (which major characteristic is being mostly sequential); generic real-time policy dedicated to real- time requests that do not fit into the multimedia access patterns; and best-effort policy dedicated to all requests without time requirements. The cache space is distributed among those policies using a reservation schema. We also propose an adaptive admission control algorithm for real-time requests relying on worst and average values of disk server utilization and adding the cache size for admission of multimedia requests. Only streams satisfying the admission algorithm criteria are accepted for further processing by the servers. All this work is based on the functionality provided by an integrated disk scheduler that is able of prioritizing the requests using their priority and deadline, like the one we proposed in [4,5,3] or the one proposed in [21]. When talking about multimedia caching, GIC is the preferred algorithm. This is an interval caching algorithm that selects the smallest intervals to be cached. This paper demonstrates that there are other interval-based caching methods that achieve better performance. The layout of the paper is as follows. Section 2 presents some related works. Section 3 describes the Proceedings of the First International Conference on Automated Production of Cross Media Content for Multi-Channel Distribution (AXMEDIS’05) 0-7695-2348-X/05 $20.00 © 2005 IEEE