1.1. Preface
MMOG (Massively Multiplayer Online Game) could be the biggest revolution in computer game industry in recent years. As network technology evolved rapidly, thousands or millions of people can login into the same virtual world, stand at the same position, and play the same game together just like they are virtually in the same room at the same place. This has been such a great success since Korea became the world largest exporter of online games in the year of 2002, and it is now a billion-scale global market expected to continue its impressive growth.
1.2. Motivation
However, right now, it takes at least three two to three years and $20 million USD to build a MMOG, due to challenges in the areas of engineering, asset-creation, and marketing. For engineering, to build an enterprise-level network infrastructure that can scale to millions of simultaneous users would be daunting for almost any game developer. It’s basically outside their area of interest and expertise. As a result, numbers of middleware solutions for game developers to ease the development cost for MMOG has shown up since the year of 2004. Also, several open-source projects have been created to provide free solution. It seems like they all try to answer to the question about MMOG scalability and flexibility and to claim the significantly benefit that hide the complexities of server through the provided platforms.
Although there’s no in-depth comparison among all of them, from the titles that are based on these middleware solutions, we observed that the scalabilities of these
platforms are not as good as what we expected to see. As the real-world game designs are so complicated that make a great impact on server performances, the average number of concurrent online players falls in the range between 2000 and 9000 per server cluster, which is consist of 5 to 20 servers (so each server is only capable of 500~1000 players). For such limitation, most virtual game worlds are replicated into several independent worlds (called shards), in which players cannot communicate with each other due to the geographical constraint. To address the shard problem, recently the Project Darkstar initiated by Sun Microsystems announced their new technology to build “shardless” MMOGs. However the number of concurrent players per server is still low and therefore the cost for entire server cluster remains high. Also, their shardless technology is based on dynamic allocation on pre-defined fixed game region, which limits the provisioning efficiency due to the synchronization overhead of those mirror servers.
We looked into the scalability problem in most of the commercial off-the-shelf MMOG platforms as well as the open source ones, and tried to propose a solution that can really scale up to a very large number of concurrent players on a single server.
1.3. Problem Description
Designing a reusable, flexible, easy-to-use MMOG platform is challenging.
Despite of the usability, the performance metrics are also significant, such as the scalability of MMOG. Scalability is usually the key to operating cost, because the higher scalability the platform is, the lower machine needed to be deployed, which results in lower cost.
Even the with the modernist design of MMOG platform, like EVE Online, the
maximum number of concurrent players ever recorded is 22020. Other than that, as mentioned above, most of each server cluster ranges from 2000 to 9000. As far as we are concern, this is a relatively poor record compared to other internet service such as web server.
To see why, we need to know that the design constraints of MMOG platforms are unique, that is, tens of thousands or millions of players log in the same virtual world to interact with each other, and results in an aggressive amount of commands and updates generated as players move and attack. Therefore, the server cluster needs to process all the commands and sends all the updates to players within a limited time constraint. Lots of researchers put their eye on reducing the network latency to give more time to serve requests. The proposed communication architectures include peer-to-peer architecture and the scalable server/proxy architecture. They all succeed to reduce the network latency to have more concurrent players within acceptable time delay; however the maximum concurrent players is still far from 10k, which is the capability that a scalable server should have generally. There should be some other bottleneck in the design.
In our point of view, since the network technology evolved rapidly that the optical interconnection is popping out of the surface and the broadband internet access is becoming the majority, the transmission delay between the server and the client has dropped to a certain level. Eventually, the network latency will not be an issue in the near future, and we will spend the most of processing time for client commands.
Basically, due to the current CPU architecture, CPU is not capable of large amount of data, which is most likely the case of MMOG. Although multi-core CPU has come to market, the memory bandwidth between CPU and main memory is still low, and multiple cache-misses occurred for the sake of limited resources and different
execution contexts of the game logics and network handlers. Also, different thread executions need synchronization and atomic locking operation to avoid update conflicts. Apparently, these constraints damage the performance and limit the throughput of executing client commands on CPU.
1.4. Research Objectives
As we identify the kernel of the problem is due to the architecture of CPU, we began to search for methods to efficiently process significant amount the client commands and update the entire virtual world. Our final answer is GPU. For last decade, GPU has been transformed from a simple 3D rendering acceleration silicon into an array of SIMD processors [3]. According to survey, the computation power of GPU is more than 100 times than CPU, and also, the memory bandwidth between the processor and the device memory of GPU is much larger than that of CPU. In general, GPU has been specialized for both compute-intensive and highly parallel computation, and the computation power of GPU has been grown rapidly even beyond Moore’s Law [4]. From the year of 2003, some researcher began to make use of GPU to do general purpose computation by mapping the general purpose problems into a 3D rendering problems. These problems range from collision detection [5] to online databases [6]. In all of the studies, the performance boost by 10 to 100 times is observed by exploiting GPU computation.
However, until now, none work has been done toward applying GPU to MMOG platform design. The most possible reason for that could be the complicated calculation and update conflict problem in the MMOG platform. But with the latest evolution of GPU technology, which will be discussed on the next chapter, it seems like GPU is ready and will become a possible choice to migrate the computation load
from CPU to GPU.
To summarize, as discussed above, for the reason that the computation problem in MMOG is computation-intensive and highly data-parallel, we want to apply GPU to general purpose computation on MMOG platform to reduce the overhead in logic processing and game world updates.
1.5. Research Contribution
This thesis discussed the issue of the barrier to build a MMOG server on GPU and proposed a practical solution and system on GPU to handle all client commands and updates. Based on different programming paradigm (sequential vs. parallel), the MMOG server needs to be re-designed to parallelize all works on GPU. New algorithms specialized to process client commands in parallel and to update the virtual world with respect to update conflicts are proposed.