Capriccio: Scalable Threads for Internet Services, R. V. Behren, J. Condit, F. Zhou, G. C. Necula, E. Brewer, Proc. of the Nineteenth Symposium on Operating System Principles (SOSP-19), Lake George, New York. October 2003, pp. 268-281.
Thread-based versus event-based programming has been a popular topic recently. For this paper, the authors have shown a strong motivation and contribution such as developing a scalable thread packet for use with high-concurrency servers which is called Capriccio.
The authors have noticed a lot of disadvantages of using event-based programming. For instance, the “stack ripping” where programmers have to save and restore live state is too complicated to use. The authors believed that by using thread-based could make life easier and could also achieve high currency just like the event-based programming as well.
In order to make thread-based model to be better than event-based model, they have build the thread package under the user-level threads, due to the fact that the user-level thread have more advantages in term of performance and flexibility over the kernel one. The implementation of Capriccio is amazing such that we don’t have to modify our applications to be able to use features from the thread package. Capriccio uses and takes advantages of new mechanisms from the latest Linux for its synchronization, I/O and Scheduling mechanisms. This is the reason why the result from the benchmark which they showed in the paper is surprisingly good for thread creation, context switch and so on; it is faster when comparing to the original Linux threads and the others comparators.
The idea of introducing linked stack management, resource-aware scheduling, blocking graph and modify some algorithm are surely improve the system utilization. Base on the performance from their evaluation which they compare between the default web servers such as Apache, Haboob, the results looks realistic. Because of the benchmarks they use are the real world application, and the Capriccio performs very well for both scalability and scheduling.
However, we already know that there must be some disadvantages of using thread-based model. One of them which I am very concerned is the issue when having multiple processors for both homogeneous and heterogeneous chip types. The authors mentioned the drawback of user-level threading such that it could make it more difficult to take advantage of multiple processors. As we know, SMP (symmetric multiprocessing) or CMP (chip multi processor) like Intel duo core has been increasing in the computer market these days. I wonder if the thread-based model will take advantages of having multiple processors more than the event-based model or not. What if we try to fix both user-level and kernel level threads instead of employ only the user-thread level. The future work section in the paper doesn’t give much detail regarding to the issue.
Lastly, I would rate the significant of this paper 5/5 (breakthrough) because they have use and modify many mechanisms and creating a new thread packet to show us that thread-based programming is better to use for high-concurrency internet servers. Their dedication and ideas are impressive