Why doesn't my threaded .Net app scale linearly when allocating large amounts of memory?

Question

I’ve run into something strange about the effect of large memory allocations on the scalability of the .Net runtime. In my test application I create lots of strings in a tig

Answer 1

Great question Luke! I'm very interested in the answer.

I suspect that you were not expecting linear scaling, but something better than a 39% variance.

NoBugz - Based on 280Z28's links, there would actually be a GC heap per core with GCMode=Server. There should also be a GC thread per heap. This shouldn't result in the concurrency issues you mention?

ran into a similar problem that was due to the fact that the CLR performs inter-thread synchronization when allocating memory to avoid overlapping allocations. Now, with the server GC, the locking algorithm may be different - but something along those same lines may be affecting your code

LBushkin - I think that that is the key question, does GCMode=Server still cause inter-thread locking when allocating memory? Anyone know - or can it simply be explained by hardware limitations as mentioned by SuperMagic?