Ankh Morpork's Finest Coder
Sunday, November 28, 2004

Programming Multiprocessors with .Net
Use Mscorsvr.dll for MP Machines
For stand-alone middle-tier and server applications, make sure mscorsvr is being used for multiprocessor machines. Mscorwks is not optimized for scaling or throughput, while the server version has several optimizations that allow it to scale well when more than one processor is available.

The mscorwks.dll is the core .NET assembly for a NT/2000/XP workstation.

The CLR has two different GCs: Workstation (mscorwks.dll) and Server (mscorsvr.dll). When running in Workstation mode, latency is more of a concern than space or efficiency. A server with multiple processors and clients connected over a network can afford some latency, but throughput is now a top priority. Rather than shoehorn both of these scenarios into a single GC scheme, Microsoft has included two garbage collectors that are tailored to each situation.

Server GC:
Multiprocessor (MP) Scalable, Parallel
One GC thread per CPU
Program paused during marking

Workstation GC:
Minimizes pauses by running concurrently during full collections

The server GC is designed for maximum throughput, and scales with very high performance. Memory fragmentation on servers is a much more severe problem than on workstations, making garbage collection an attractive proposition. In a uniprocessor scenario, both collectors work the same way: workstation mode, without concurrent collection. On an MP machine, the Workstation GC uses the second processor to run the collection concurrently, minimizing delays while diminishing throughput. The Server GC uses multiple heaps and collection threads to maximize throughput and scale better.


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